publications

2025

1. arXiv

   Cloudy-Maraston: Integrating nebular continuum and line emission with the Maraston stellar population synthesis models

   Sophie L. Newman, Christopher C. Lovell, Claudia Maraston, and 5 more authors

   Jan 2025

   arXiv:2501.03133 [astro-ph]

   Abs DOI

   The James Webb Space Telescope has ushered in an era of abundant high-redshift observations of young stellar populations characterized by strong emission lines, motivating us to integrate nebular emission into the new Maraston stellar population model which incorporates the latest Geneva stellar evolutionary tracks for massive stars with rotation. We use the photoionization code Cloudy to obtain the emergent nebular continuum and line emission for a range of modelling parameters, then compare our results to observations on various emission line diagnostic diagrams. We carry out a detailed comparison with several other models in the literature assuming different input physics, including modified prescriptions for stellar evolution and the inclusion of binary stars, and find close agreement in the H{}rm }beta H{}rm }alpha [N II]{}lambda 6583 and [S II]{}lambda 6731 luminosities between the models. However, we find significant differences in lines with high ionization energies, such as He II{}lambda\1640 and [O III]{}lambda 5007 due to large variations in the hard ionizing photon production rates. The models differ by a maximum of {}hat{Q}_{}rm [O III]}lambda 5007} = }rm 6 }times 10^9 }; s^{-1} }, M_{}odot}^{-1} where these differences are mostly caused by the assumed stellar rotation and effective temperatures for the Wolf Rayet phase. Interestingly, rotation and uncorrected effective temperatures in our single star population models alone generate [O III] ionizing photon production rates higher than models including binary stars with ages between 1 to 8 Myr. These differences highlight the dependence of derived properties from SED fitting on the assumed model, as well as the sensitivity of predictions from cosmological simulations.

2. ApJ

   EPOCHS. IV. SED Modeling Assumptions and Their Impact on the Stellar Mass Function at 6.5 ≤ z ≤ 13.5 Using PEARLS and Public JWST Observations

   Thomas Harvey, Christopher J. Conselice , Nathan J. Adams, and 31 more authors

   ApJ, Jan 2025

   Publisher: IOP ADS Bibcode: 2025ApJ...978...89H

   Abs DOI

   We utilize deep JWST Near Infrared Camera (NIRCam) observations for the first direct constraints on the Galaxy Stellar Mass Function (GSMF) at z \textgreater 10. Our EPOCHS v1 sample includes 1120 galaxy candidates at 6.5 \textless z \textless 13.5 taken from a consistent reduction and analysis of publicly available deep JWST NIRCam data covering the Prime Extragalactic Areas for Reionization Science, CEERS, GLASS, JADES GOOD-S, NGDEEP, and SMACS0723 surveys, totaling 187 arcmin2. We investigate the impact of spectral energy distribution fitting methods, assumed star formation histories (SFHs), dust laws, and priors on galaxy masses and the resultant GSMF. While our fiducial GSMF agrees with the literature at z \textless 13.5, we find that the assumed SFH model has a large impact on the GSMF and stellar mass density (SMD), finding a 0.75 dex increase in the SMD at z = 10.5 between a flexible nonparametric and standard parametric SFH. Overall, we find a flatter SMD evolution at z ≥ 9 than some studies predict, suggesting a rapid buildup of stellar mass in the early Universe. We find no incompatibility between our results and those of standard cosmological models, as suggested previously, although the most massive galaxies may require a high star formation efficiency. We find that the "little red dot" galaxies dominate the z = 7 GSMF at high masses, necessitating a better understanding of the relative contributions of active galactic nucleus and stellar emission. We show that assuming a theoretically motivated top-heavy initial mass function (IMF) reduces stellar mass by 0.5 dex without affecting fit quality, but our results remain consistent with existing cosmological models with a standard IMF.

2024

1. MNRAS

   First Light And Reionisation Epoch Simulations (FLARES) - XII: The consequences of star-dust geometry on galaxies in the EoR

   Aswin P. Vijayan, Peter A. Thomas, Christopher C. Lovell, and 5 more authors

   MNRAS, Jan 2024

   ADS Bibcode: 2024MNRAS.527.7337V

   Abs DOI

   Using the First Light And Reionisation Epoch Simulations, a suite of hydrodynamical simulations, we explore the consequences of a realistic model for star-dust geometry on the observed properties of galaxies. We find that the ultraviolet (UV) attenuation declines rapidly from the central regions of galaxies, and bright galaxies have spatially extended star formation that suffers less obscuration than their fainter counterparts, demonstrating a non-linear relationship between the UV luminosity and the UV attenuation, giving a double power-law shape to the UVLF. Spatially distinct stellar populations within galaxies experience a wide range of dust attenuation due to variations in the dust optical depth along their line of sight, which can range from completely dust obscured to being fully unobscured. The overall attenuation curve of a galaxy is then a complex combination of various lines of sight within the galaxy. We explore the manifestation of this effect to study the reliability of line ratios to infer galaxy properties, in particular, the Balmer decrement and the Baldwin, Phillips, and Terlevich (BPT) diagram. We find the Balmer decrement predicted Balmer-line attenuation to be higher (factor of 1 to ≳ 10) than expected from commonly used attenuation curves. The observed BPT line ratios deviate from their intrinsic values [median difference of 0.08 (0.02) and standard deviation of 0.2 (0.05) for log10([N\{}small II}]}lambda 6585/\Hα) (log10([O III]λ5008/Hβ)]. Finally, we explore the variation in observed properties (UV attenuation, UV slope, and Balmer decrement) with viewing angle, finding average differences of ~0.3 mag in the UV attenuation.

2. MNRAS

   First Light and Reionization Epoch Simulations (FLARES) - XIV. The Balmer/4000 Å breaks of distant galaxies

   Stephen M. Wilkins, Christopher C. Lovell, Dimitrios Irodotou, and 10 more authors

   MNRAS, Jan 2024

   ADS Bibcode: 2024MNRAS.527.7965W

   Abs DOI

   With the successful launch and commissioning of JWST we are now able to routinely spectroscopically probe the rest-frame optical emission of galaxies at z \textgreater 6 for the first time. Among the most useful spectral diagnostics used in the optical is the Balmer/4000 Å break; this is, in principle, a diagnostic of the mean ages of composite stellar populations. However, the Balmer break is also sensitive to the shape of the star formation history, the stellar (and gas) metallicity, the presence of nebular continuum emission, and dust attenuation. In this work, we explore the origin of the Balmer/4000 Å break using the SYNTHESIZER synthetic observations package. We then make predictions of the Balmer/4000 Å break using the First Light and Reionization Epoch Simulations at 5 \textless z \textless 10. We find that the average break strength weakly correlates with stellar mass and rest-frame far-ultraviolet luminosity, but that this is predominantly driven by dust attenuation. We also find that break strength provides a weak diagnostic of the age but performs better as a means to constrain star formation and stellar mass, alongside the ultraviolet and optical luminosity, respectively.

3. arXiv

   On the Significance of Rare Objects at High Redshift: The Impact of Cosmic Variance

   Christian Kragh Jespersen, Charles L. Steinhardt, Rachel S. Somerville, and 1 more author

   Feb 2024

   Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240300050K

   Abs

   The discovery of extremely luminous galaxies at ultra-high redshifts (\zrsim 8\) has posed a challenge for galaxy formation models. Most statistical analyses of this tension to date have not properly accounted for the variance due to field-to-field clustering, which causes the number counts of galaxies to vary from field to field, greatly in excess of Poisson noise. This super-Poissonian variance is often referred to as cosmic variance. Since cosmic variance increases rapidly as a function of mass, redshift, and for small observing areas, the most massive objects in deep }textit{JWST} surveys are severely impacted by cosmic variance. In this paper, we introduce a simple model to predict the distribution of the mass of the most massive galaxy found for different survey designs, which includes cosmic variance. The distributions differ significantly from previous predictions using the Extreme Value Statistics formalism, changing both the position and shape of the distribution of most massive galaxies in a counter-intuitive way. We test our model using the }texttt{UniverseMachine} simulations, where the predicted effects of including cosmic variance are clearly identifiable. Moreover, we find that the highly significant skew in the distributions of galaxy number counts for typical deep }textit{JWST} surveys lead to a high "variance on the variance", which greatly impacts the calculation of the cosmic variance itself. We conclude that it is crucial to accurately account for the impact of cosmic variance in any future analysis of tension between extreme galaxies in the early universe and galaxy formation models.

4. arXiv e-prints

   Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Surveying the distant Universe

   Eelco Kampen, Tom Bakx, Carlos De Breuck, and 27 more authors

   arXiv e-prints, Mar 2024

   Abs

   During the most active period of star formation in galaxies, which occurs in the redshift range 1\textlessz\textless3, strong bursts of star formation result in significant quantities of dust, which obscures new stars being formed as their UV/optical light is absorbed and then re-emitted in the infrared, which redshifts into the mm/sub-mm bands for these early times. To get a complete picture of the high-z galaxy population, we need to survey a large patch of the sky in the sub-mm with sufficient angular resolution to resolve all galaxies, but we also need the depth to fully sample their cosmic evolution, and therefore obtain their redshifts using direct mm spectroscopy with a very wide frequency coverage. This requires a large single-dish sub-mm telescope with fast mapping speeds at high sensitivity and angular resolution, a large bandwidth with good spectral resolution and multiplex spectroscopic capabilities. The proposed 50-m Atacama Large Aperture Submillimeter Telescope (AtLAST) will deliver these specifications. We discuss how AtLAST allows us to study the whole population of high-z galaxies, including the dusty star-forming ones which can only be detected and studied in the sub-mm, and obtain a wealth of information for each of these up to z~7: gas content, cooling budget, star formation rate, dust mass, and dust temperature. We present worked examples of surveys that AtLAST can perform, both deep and wide, and also focused on galaxies in proto-clusters. In addition we show how such surveys with AtLAST can measure the growth rate and the Hubble constant with high accuracy, and demonstrate the power of the line-intensity mapping method in the mm/sub-mm wavebands to constrain the cosmic expansion history at high redshifts, as good examples of what can uniquely be done by AtLAST in this research field.

5. arXiv

   Like a candle in the wind: The embers of once aflame, now smouldering galaxies at \5 \textless z \textless 8\

   James Trussler, Christopher Conselice , Nathan Adams, and 8 more authors

   Apr 2024

   Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240407163T

   Abs DOI

   We develop a photometric search method for identifying smouldering galaxies at \5\textless z \textless 8 which are defined to have weak emission lines and thus generally have low specific star formation rates and may even be in a state of (temporary) quiescence. The deep NIRCam imaging (\{}sim}29.5 AB mag, 5{}sigma\) from the JADES second data release is essential for finding these systems, as they are faint, relatively quiescent dwarf galaxies (\M_* }sim 10^{8}\-\10^9 {}mathrm{M}_}odot) in the Epoch of Reionisation (EoR). Moreover, medium-band imaging is key, enabling a clear identification of the lack of emission lines in these galaxies, thus betraying their dormant flame. Owing to the young age of the Universe, combined with the likely bursty star formation in these first dwarf galaxies, conventional colour-selection methods like the UVJ diagram likely miss a large fraction of the quiescent population in the EoR. Indeed, we find that smouldering galaxies constitute a considerable fraction (0.10-0.35) of the EoR dwarf galaxy population (\M_* }sim 10^{8}\-\10^{9} {}mathrm{M}_}odot\). As predicted by simulations, these first dwarf galaxies are fragile, the star formation in their shallow potential wells easily snuffed out by feedback-driven winds triggered by secular or merger-driven starbursts, with the smouldering fraction increasing with decreasing stellar mass. Finally, we provide observational constraints on the smouldering galaxy comoving number density (\{}sim}10^{-4}\-\10^{-5} dex{^{-1} Mpc{^{-3}\), which, although hampered by incompleteness, should aid in our understanding of the primordial baryon cycle, as current simulations greatly disagree on whether these systems are rare (\{}sim}1}%\) or common (\{}sim}50}%\) in the EoR.

6. arXiv

   Tracing the evolutionary pathways of dust and cold gas in high-z quiescent galaxies with SIMBA

   G. Lorenzon, D. Donevski, K. Lisiecki, and 13 more authors

   Apr 2024

   Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240410568L

   Abs DOI

   Recent discoveries of copious amounts of dust in quiescent galaxies (QGs) at high redshifts (\zrsim 1-2\) challenge the conventional view that these objects have poor interstellar medium (ISM) in proportion to their stellar mass. We use the SIMBA cosmological simulation to explore the evolution of dust and cold gas content in QGs in relation to the quenching processes affecting them. We track the changes in the ISM dust abundance across the evolutionary history of QGs identified at \0 }lesssim z }lesssim2 in the field and cluster environments. The QGs quench via diverse pathways, both rapid and slow, and exhibit a wide range of times elapsed between the quenching event and cold gas removal (from {}sim650 Myr to {}sim8 Gyr). We find that quenching modes attributed to the feedback from active galactic nuclei (AGN) do not affect dust and cold gas within the same timescales. Remarkably, QGs may replenish their dust content in the quenched phase primarily due to internal processes and marginally by external factors such as minor mergers. The key mechanism for re-formation of dust is prolonged grain growth on gas-phase metals, it is effective within {}sim100 Myr after the quenching event, and rapidly increases the dust-to-gas mass ratio in QGs above the standard values ({}delta_{}rm DGR}rsim1/100\). As a result, despite heavily depleted cold gas reservoirs, roughly half of QGs maintain little evolution in their ISM dust with stellar age within the first 2 Gyr following the quenching. Overall, we predict that relatively dusty QGs (\M_{}rm dust}/M_{}star}rsim10^{-3}-10^{-4}\) arise from both fast and slow quenchers, and are prevalent in systems of intermediate and low stellar masses (\9\textless}log(M_{}star}/M_{}odot})\textless10.5\). This prediction poses an immediate quest for observational synergy between e.g., James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA).

7. arXiv

   The JWST EXCELS survey: Too much, too young, too fast? Ultra-massive quiescent galaxies at 3 \textless z \textless 5

   A. C. Carnall, F. Cullen, R. J. McLure, and 21 more authors

   arXiv, May 2024

   Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240502242C

   Abs DOI

   We report ultra-deep, medium-resolution spectroscopic observations for 4 quiescent galaxies with log\_{10}(M_*/}mathrm{M_}odot})\textgreater11 at \3 \textless z \textless 5\. These data were obtained with JWST NIRSpec as part of the Early eXtragalactic Continuum and Emission Line Science (EXCELS) survey, which we introduce in this work. The first pair of galaxies are newly selected from PRIMER UDS imaging, both at \z=4.62 and separated by \860 pkpc on the sky, within a larger structure for which we confirm several other members. These galaxies formed at \z}simeq8-10 and, despite their similar stellar masses, ages, and their proximity, they exhibit very different stellar metallicities, hinting at different formation pathways. These systems could plausibly merge by the present day to produce a local massive elliptical galaxy. The other 2 ultra-massive quiescent galaxies are previously known at \z=3.99 and \3.19 with the latter (ZF-UDS-7329) having been the subject of debate as potentially too old and too massive to be accommodated by the {}Lambda\-CDM halo-mass function. Both exhibit high stellar metallicities, and for ZF-UDS-7329 we are able to measure the {}alpha-\enhancement, obtaining [Mg/Fe] = \0.42^{+0.19}_{-0.17}\. We finally evaluate whether these 4 galaxies are consistent with the {}Lambda\-CDM halo-mass function using an extreme value statistics approach. We find that the \z=4.62 objects and the \z=3.19 object are unlikely within our area under the assumption of standard stellar fractions (\f_*}simeq0.1-0.2\). However, these objects roughly align with the most massive galaxies expected under the assumption of 100 per cent conversion of baryons to stars (\f_*\=1). Our results suggest extreme galaxy formation physics during the first billion years, but no conflict with {}Lambda\-CDM cosmology.

8. arXiv

   First Light And Reionisation Epoch Simulations (FLARES) XVI: Size Evolution of Massive Dusty Galaxies at Cosmic Dawn from UV to IR

   Paurush Punyasheel, Aswin P. Vijayan, Thomas R. Greve, and 9 more authors

   Aug 2024

   Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240811037P

   Abs

   We use the First Light And Reionisation Epoch Simulations (FLARES) to study the evolution of the rest-frame ultraviolet (UV) and far-infrared (FIR) sizes for a statistical sample of massive (\rsim10^{9}\M\_{}odot}\) high redshift galaxies (z {}in [5,10]). Galaxies are post-processed using the SKIRT radiative transfer code, to self-consistently obtain the full spectral energy distribution and surface brightness distribution. We create mock observations of the galaxies for the Near Infrared Camera (NIRCam) to study the rest-frame UV 1500 {}unicode{xC5} morphology. We also generate mock rest-frame FIR (50 {}mu\m) photometry and mock ALMA (158 {}mu\m) (0.01"-0.03" and {}approx\0.3" angular resolution) observations to study the dust-continuum. We find the effect of dust on observed sizes reduces with increasing wavelength from the UV to optical ({}sim\0.6 times the UV at 0.4{}mu\m), with no evolution in FIR sizes. Observed sizes vary within 0.4-1.2 times the intrinsic sizes at different signal to noise ratios (SNR = 5-20) across redshifts. The effect of PSF and noise makes bright structures prominent, whereas fainter regions blend with noise, leading to an underestimation (factor of 0.4-0.8) of sizes at SNR=5. At SNR=15-20, the underestimation reduces (factor of 0.6-0.9) at z=5-8 but due to PSF, at z=9-10, bright cores are dominant, resulting in an overestimation (factor of 1.0-1.2). For ALMA, low resolution sizes are effected by noise which acts as extended emission. The size evolution in UV broadly agrees with current observational samples and other simulations. This work is one of the first to analyse the panchromatic sizes of a statistically significant sample of simulated high-redshift galaxies, complementing a growing body of research highlighting the importance of conducting an equivalent comparison between observed galaxies and their simulated counterparts in the early Universe.

9. MNRAS

   Star formation efficiency across large-scale galactic environments

   Laya Ghodsi, Allison W. S. Man, Darko Donevski, and 4 more authors

   MNRAS, Mar 2024

   Publisher: OUP ADS Bibcode: 2024MNRAS.528.4393G

   Abs DOI

   Environmental effects on the formation and evolution of galaxies have been one of the leading questions in galaxy studies during the past few decades. In this work, we investigate the relationship between the star formation activity of galaxies and their environmental matter density using the cosmological hydrodynamic simulation SIMBA. The galactic star formation activity indicators that we explore include the star formation efficiency (SFE), specific star formation rate (sSFR), and molecular hydrogen mass fraction (\f^{*}_{}mathrm{H_2}}\), and the environment is considered as the large-scale environmental matter density, calculated based on the stellar mass of nearby galaxies on a 1 h-1 Mpc grid using the cloud in cell method. Our sample includes galaxies with \9 }log }frac{M_*}{{}rm M}_{}odot }} at 0 \textless z \textless 4, divided into three stellar mass bins to disentangle the effects of stellar mass and environment on the star formation activity of galaxies. For low- to intermediate-mass galaxies at low redshifts (z \textless 1.5), we find that the star formation efficiency of those in high-density regions are ~0.3 dex lower than those in low-density regions. However, there is no significant environmental dependence of the star formation efficiency for massive galaxies over all our redshift range, and low- to intermediate-mass galaxies at high redshifts (z \textgreater 1.5). We present a scaling relation for the depletion time of cold molecular hydrogen (tdepl = 1/SFE) as a function of galaxy parameters including environmental density. Our findings provide a framework for quantifying the environmental effects on the star formation activities of galaxies as a function of stellar mass and redshift. The most significant environmental dependence is seen at later cosmic times (z \textless 1.5) and towards lower stellar masses (\9 }log }frac{M_*}{{}rm M}_{}odot }} 10\). Future large galaxy surveys can use this framework to look for the environmental dependence of the star formation activity and examine our predictions.

10. ApJ

    Outshining by Recent Star Formation Prevents the Accurate Measurement of High-z Galaxy Stellar Masses

    Desika Narayanan, Sidney Lower, Paul Torrey, and 10 more authors

    ApJ, Jan 2024

    Publisher: IOP ADS Bibcode: 2024ApJ...961...73N

    Abs DOI

    We demonstrate that the inference of galaxy stellar masses via spectral energy distribution (SED) fitting techniques for galaxies formed in the first billion years after the Big Bang carries fundamental uncertainties owing to the loss of star formation history (SFH) information from the very first episodes of star formation in the integrated spectra of galaxies. While this early star formation can contribute substantially to the total stellar mass of high-redshift systems, ongoing star formation at the time of detection outshines the residual light from earlier bursts, hampering the determination of accurate stellar masses. As a result, order-of-magnitude uncertainties in stellar masses can be expected. We demonstrate this potential problem via direct numerical simulation of galaxy formation in a cosmological context. In detail, we carry out two cosmological simulations with significantly different stellar feedback models, which span a significant range in SFH burstiness. We compute the mock SEDs for these model galaxies at z = 7 via calculations of 3D dust radiative transfer, and then backward fit these SEDs with PROSPECTOR SED fitting software. The uncertainties in derived stellar masses that we find for z \textgreater 7 galaxies motivate the development of new techniques and/or priors for SFH to model star formation in the early Universe.

11. MNRAS

    Cosmological baryon spread and impact on matter clustering in CAMELS

    Matthew Gebhardt, Daniel Anglés-Alcázar, Josh Borrow, and 9 more authors

    MNRAS, Apr 2024

    Publisher: OUP ADS Bibcode: 2024MNRAS.529.4896G

    Abs DOI

    We quantify the cosmological spread of baryons relative to their initial neighbouring dark matter distribution using thousands of state-of-the-art simulations from the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project. We show that dark matter particles spread relative to their initial neighbouring distribution owing to chaotic gravitational dynamics on spatial scales comparable to their host dark matter halo. In contrast, gas in hydrodynamic simulations spreads much further from the initial neighbouring dark matter owing to feedback from supernovae (SNe) and active galactic nuclei (AGN). We show that large-scale baryon spread is very sensitive to model implementation details, with the fiducial SIMBA model spreading ~40 per cent of baryons \textgreater1 Mpc away compared to ~10 per cent for the IllustrisTNG and ASTRID models. Increasing the efficiency of AGN-driven outflows greatly increases baryon spread while increasing the strength of SNe-driven winds can decrease spreading due to non-linear coupling of stellar and AGN feedback. We compare total matter power spectra between hydrodynamic and paired N-body simulations and demonstrate that the baryonic spread metric broadly captures the global impact of feedback on matter clustering over variations of cosmological and astrophysical parameters, initial conditions, and (to a lesser extent) galaxy formation models. Using symbolic regression, we find a function that reproduces the suppression of power by feedback as a function of wave number (k) and baryonic spread up to \k }sim 10}, h Mpc-1 in SIMBA while highlighting the challenge of developing models robust to variations in galaxy formation physics implementation.

12. MNRAS

    iMaNGA: mock MaNGA galaxies based on IllustrisTNG and MaStar SSPs. - III. Stellar metallicity drivers in MaNGA and TNG50

    Lorenza Nanni, Justus Neumann, Daniel Thomas, and 6 more authors

    MNRAS, Jan 2024

    Publisher: OUP ADS Bibcode: 2024MNRAS.527.6419N

    Abs DOI

    The iMaNGA project uses a forward-modelling approach to compare the predictions of cosmological simulations with observations from SDSS-IV/MaNGA. We investigate the dependency of age and metallicity radial gradients on galaxy morphology, stellar mass, stellar surface mass density (Σ*), and environment. The key of our analysis is that observational biases affecting the interpretation of MaNGA data are emulated in the theoretical iMaNGA sample. The simulations reproduce the observed global stellar population scaling relations with positive correlations between galaxy mass and age/metallicity quite well and also produce younger stellar populations in late-type in agreement with observations. We do find interesting discrepancies, though, that can inform the physics and further development of the simulations. Ages of spiral galaxies and low-mass ellipticals are overestimated by about 2-4 Gyr. Radial metallicity gradients are steeper in iMaNGA than in MaNGA, a discrepancy most prominent in spiral and lenticular galaxies. Also, the observed steepening of metallicity gradients with increasing galaxy mass is not well matched by the simulations. We find that the theoretical radial profiles of surface mass density Σ* are steeper than in observations except for the most massive galaxies. In both MaNGA and iMaNGA [Z/H] correlates with Σ*, however, the simulations systematically predict lower [Z/H] by almost a factor of 2 at any Σ*. Most interestingly, for galaxies with stellar mass log M* ≤ 10.80 M⊙, the MaNGA data reveal a positive correlation between galaxy radius and [Z/H] at fixed Σ*, which is not recovered in iMaNGA. Finally, the dependence on environmental density is negligible in both the theoretical iMaNGA and the observed MaNGA data.

13. arXiv

    First Light and Reionization Epoch Simulations (FLARES) – XV: The physical properties of super-massive black holes and their impact on galaxies in the early universe

    Stephen M. Wilkins, Jussi K. Kuusisto, Dimitrios Irodotou, and 9 more authors

    Apr 2024

    Publication Title: arXiv e-prints ADS Bibcode: 2024arXiv240402815W

    Abs DOI

    Understanding the co-evolution of super-massive black holes (SMBHs) and their host galaxies remains a key challenge of extragalactic astrophysics, particularly the earliest stages at high-redshift. However, studying SMBHs at high-redshift with cosmological simulations, is challenging due to the large volumes and high-resolution required. Through its innovative simulation strategy, the First Light And Reionisation Epoch Simulations (FLARES) suite of cosmological hydrodynamical zoom simulations allows us to simulate a much wider range of environments which contain SMBHs with masses extending to \M_{}bullet}\textgreater10^{9}} M_{}odot} at \z=5\. In this paper, we use FLARES to study the physical properties of SMBHs and their hosts in the early Universe (\5}le}, z }le10\). FLARES predicts a sharply declining density with increasing redshift, decreasing by a factor of 100 over the range \z=5}to 10\. Comparison between our predicted bolometric luminosity function and pre-}emph{JWST} observations yield a good match. However, recent }emph{JWST} observations appear to suggest a larger contribution of SMBHs than previously observed, or predicted by FLARES. Finally, by using a re-simulation with AGN feedback disabled, we explore the impact of AGN feedback on their host galaxies. This reveals that AGN feedback results in a reduction of star formation activity, even at \z\textgreater5 but only in the most massive galaxies. A deeper analysis reveals that AGN are also the cause of suppressed star formation in passive galaxies but that the presence of an AGN doesn’t necessarily result in the suppression of star formation.

14. OJA

    LtU-ILI: An All-in-One Framework for Implicit Inference in Astrophysics and Cosmology

    Matthew Ho, Deaglan J. Bartlett, Nicolas Chartier, and 12 more authors

    OJA, Jul 2024

    ADS Bibcode: 2024OJAp....7E..54H

    Abs DOI

    This paper presents the Learning the Universe Implicit Likelihood Inference (LtU-ILI) pipeline, a codebase for rapid, user-friendly, and cutting-edge machine learning (ML) inference in astrophysics and cosmology. The pipeline includes software for implementing various neural architectures, training schema, priors, and density estimators in a manner easily adaptable to any research workflow. It includes comprehensive validation metrics to assess posterior estimate coverage, enhancing the reliability of inferred results. Additionally, the pipeline is easily parallelizable, designed for efficient exploration of modeling hyperparameters. To demonstrate its capabilities, we present real applications across a range of astrophysics and cosmology problems, such as: estimating galaxy cluster masses from X-ray photometry; inferring cosmology from matter power spectra and halo point clouds; characterising progenitors in gravitational wave signals; capturing physical dust parameters from galaxy colors and luminosities; and establishing properties of semi-analytic models of galaxy formation. We also include exhaustive benchmarking and comparisons of all implemented methods as well as discussions about the challenges and pitfalls of ML inference in astronomical sciences. All code and examples are made publicly available at https://github.com/maho3/ltu-ili.

15. arXiv

    First Light and Reionisation Epoch Simulations (FLARES) XVII: Learning the galaxy-halo connection at high redshifts

    Maxwell G. A. Maltz, Peter A. Thomas, Christoper C. Lovell, and 6 more authors

    Oct 2024

    arXiv:2410.24082

    Abs DOI

    Understanding the galaxy-halo relationship is not only key for elucidating the interplay between baryonic and dark matter, it is essential for creating large mock galaxy catalogues from N-body simulations. High-resolution hydrodynamical simulations are limited to small volumes by their large computational demands, hindering their use for comparisons with wide-field observational surveys. We overcome this limitation by using the First Light and Reionisation Epoch Simulations (FLARES), a suite of high-resolution (M_gas = 1.8 x 10^6 M_Sun) zoom simulations drawn from a large, (3.2 cGpc)^3 box. We use an extremely randomised trees machine learning approach to model the relationship between galaxies and their subhaloes in a wide range of environments. This allows us to build mock catalogues with dynamic ranges that surpass those obtainable through periodic simulations. The low cost of the zoom simulations facilitates multiple runs of the same regions, differing only in the random number seed of the subgrid models; changing this seed introduces a butterfly effect, leading to random differences in the properties of matching galaxies. This randomness cannot be learnt by a deterministic machine learning model, but by sampling the noise and adding it post-facto to our predictions, we are able to recover the distributions of the galaxy properties we predict (stellar mass, star formation rate, metallicity, and size) remarkably well. We also explore the resolution-dependence of our models’ performances and find minimal depreciation down to particle resolutions of order M_DM ~ 10^8 M_Sun, enabling the future application of our models to large dark matter-only boxes.

16. arXiv

    Learning the Universe: Cosmological and Astrophysical Parameter Inference with Galaxy Luminosity Functions and Colours

    Christopher C. Lovell, Tjitske Starkenburg, Matthew Ho, and 9 more authors

    Nov 2024

    arXiv:2411.13960

    Abs DOI

    We perform the first direct cosmological and astrophysical parameter inference from the combination of galaxy luminosity functions and colours using a simulation based inference approach. Using the Synthesizer code we simulate the dust attenuated ultraviolet–near infrared stellar emission from galaxies in thousands of cosmological hydrodynamic simulations from the CAMELS suite, including the Swift-EAGLE, Illustris-TNG, Simba & Astrid galaxy formation models. For each galaxy we calculate the rest-frame luminosity in a number of photometric bands, including the SDSS {}textit{ugriz} and GALEX FUV & NUV filters; this dataset represents the largest catalogue of synthetic photometry based on hydrodynamic galaxy formation simulations produced to date, totalling \textgreater200 million sources. From these we compile luminosity functions and colour distributions, and find clear dependencies on both cosmology and feedback. We then perform simulation based (likelihood-free) inference using these distributions, and obtain constraints on both cosmological and astrophysical parameters. Both colour distributions and luminosity functions provide complementary information on certain parameters when performing inference. Most interestingly we achieve constraints on {}sigma_8 describing the clustering of matter. This is attributable to the fact that the photometry encodes the star formation–metal enrichment history of each galaxy; galaxies in a universe with a higher {}sigma_8 tend to form earlier and have higher metallicities, which leads to redder colours. We find that a model trained on one galaxy formation simulation generalises poorly when applied to another, and attribute this to differences in the subgrid prescriptions, and lack of flexibility in our emission modelling. The photometric catalogues are publicly available at: https://camels.readthedocs.io/ .

17. ApJ

    Unveiling the Distant Universe: Characterizing z ≥ 9 Galaxies in the First Epoch of COSMOS-Web

    Maximilien Franco, Hollis B. Akins, Caitlin M. Casey, and 48 more authors

    ApJ, Sep 2024

    Publisher: IOP ADS Bibcode: 2024ApJ...973...23F

    Abs DOI

    We report the identification of 15 galaxy candidates at z ≥ 9 using the initial COSMOS-Web JWST observations over 77 arcmin2 through four Near Infrared Camera filters (F115W, F150W, F277W, and F444W) with an overlap with the Mid-Infrared Imager (F770W) of 8.7 arcmin2. We fit the sample using several publicly available spectral energy distribution (SED) fitting and photometric redshift codes and determine their redshifts between z = 9.3 and z = 10.9 ( = 10.0), UV magnitudes between M UV = ‑21.2 and ‑19.5 (with UV\textgreater = ‑20.2), and rest-frame UV slopes (\textlessβ\textgreater = ‑2.4). These galaxies are, on average, more luminous than most z ≥ 9 candidates discovered by JWST so far in the literature, while exhibiting similar blue colors in their rest-frame UV. The rest-frame UV slopes derived from SED fitting are blue (β ∼ [‑2.0, ‑2.7]) without reaching extremely blue values as reported in other recent studies at these redshifts. The blue color is consistent with models that suggest the underlying stellar population is not yet fully enriched in metals like similarly luminous galaxies in the lower-redshift Universe. The derived stellar masses with \textlesslog10( M ⋆/M ⊙)\textgreater ≈ 8–9 are not in tension with the standard Lambda cold dark matter (ΛCDM) model, and our measurement of the volume density of such UV-luminous galaxies aligns well with previously measured values presented in the literature at z ∼ 9–10. Our sample of galaxies, although compact, is significantly resolved.

18. ApJ

    Efficient NIRCam Selection of Quiescent Galaxies at 3 \textless z \textless 6 in CEERS

    Arianna S. Long, Jacqueline Antwi-Danso, Erini L. Lambrides, and 31 more authors

    ApJ, Jul 2024

    Publisher: IOP ADS Bibcode: 2024ApJ...970...68L

    Abs DOI

    Substantial populations of massive quiescent galaxies at z ≥ 3 challenge our understanding of rapid galaxy growth and quenching over short timescales. In order to piece together this evolutionary puzzle, more statistical samples of these objects are required. Established techniques for identifying massive quiescent galaxies are increasingly inefficient and unconstrained at z \textgreater 3. As a result, studies report that as much as 70% of quiescent galaxies at z \textgreater 3 may be missed from existing surveys. In this work, we propose a new empirical color selection technique designed to select massive quiescent galaxies at 3 ≲ z ≲ 6 using JWST NIRCam imaging data. We use empirically constrained galaxy spectral energy distribution (SED) templates to define a region in the F277W ‑ F444W versus F150W ‑ F277W color plane that captures quiescent galaxies at z \textgreater 3. We apply these color selection criteria to the Cosmic Evolution Early Release Science (CEERS) Survey and use SED fitting on sources in the region to identify 44 candidate z ≳ 3 quiescent galaxies. Over half of these sources are newly discovered and, on average, exhibit specific star formation rates of poststarburst galaxies. Most of these sources would not be discovered using canonical UVJ diagrams. We derive volume density estimates of n ∼ 1–4 × 10‑5 Mpc‑3 at 3 \textless z \textless 5, finding excellent agreement with existing reports on similar populations in the CEERS field. Thanks to NIRCam’s wavelength coverage and sensitivity, this technique provides an efficient tool to search for large samples of these rare galaxies.

2023

1. MNRAS

   Extreme value statistics of the halo and stellar mass distributions at high redshift: are JWST results in tension with ΛCDM?

   Christopher C. Lovell, Ian Harrison, Yuichi Harikane, and 2 more authors

   MNRAS, Jan 2023

   ADS Bibcode: 2023MNRAS.518.2511L

   Abs DOI

   The distribution of dark matter halo masses can be accurately predicted in the lambda cold dark matter (ΛCDM) cosmology. The presence of a single massive halo or galaxy at a particular redshift, assuming some baryon and stellar fraction for the latter, can therefore be used to test the underlying cosmological model. A number of recent measurements of very large galaxy stellar masses at high redshift (z \textgreater 8) motivate an investigation into whether any of these objects are in tension with ΛCDM. We use extreme value statistics to generate confidence regions in the mass-redshift plane for the most extreme mass haloes and galaxies. Tests against numerical models show no tension, neither in their dark matter halo masses nor their galaxy stellar masses. However, we find tentative \textgreater3σ tension with recent observational determinations of galaxy masses at high redshift from both Hubble Space Telescope and James Webb Space Telescope, despite using conservative estimates for the stellar fraction (f⋆ ~ 1). Either these galaxies are in tension with ΛCDM, or there are unaccounted for uncertainties in their stellar mass or redshift estimates.

2. MNRAS

   Unveiling the main sequence of galaxies at z ≥ 5 with the JWST: predictions from simulations

   Jordan C. J. D’Silva, Claudia D. P. Lagos, Luke J. M. Davies, and 2 more authors

   MNRAS, Jan 2023

   ADS Bibcode: 2023MNRAS.518..456D

   Abs DOI

   We use two independent galaxy-formation simulations, FLARES, a cosmological hydrodynamical simulation, and SHARK, a semi-analytic model, to explore how well the JWST will be able to uncover the existence and parameters of the star-forming main sequence (SFS) at z = 5 → 10, i.e. shape, scatter, normalization. Using two independent simulations allows us to isolate predictions (e.g. stellar mass, star formation rate, SFR, luminosity functions) that are robust to or highly dependent on the implementation of the physics of galaxy formation. Both simulations predict that JWST can observe ≥70-90 per cent (for SHARK and FLARES, respectively) of galaxies up to z ~ 10 (down to stellar masses of \{}approx}10^{8.3}}rm M_{}odot } and SFRs of \{}approx}10^{0.5}{}rm M}_{}odot }},{}rm yr}^{-1}\) in modest integration times and given current proposed survey areas (e.g. the Web COSMOS 0.6 deg2) to accurately constrain the parameters of the SFS. Although both simulations predict qualitatively similar distributions of stellar mass and SFR. There are important quantitative differences, such as the abundance of massive, star-forming galaxies with FLARES predicting a higher abundance than SHARK; the early onset of quenching as a result of black hole growth in FLARES (at z ≍ 8), not seen in SHARK until much lower redshifts; and the implementation of synthetic photometry with FLARES predicting more JWST-detected galaxies (~90 per cent) than SHARK (~70 per cent) at z = 10. JWST observations will distinguish between these models, leading to a significant improvement upon our understanding of the formation of the very first galaxies.

3. MNRAS

   First light and reionization epoch simulations (FLARES) V: the redshift frontier

   Stephen M. Wilkins, Aswin P. Vijayan, Christopher C. Lovell, and 7 more authors

   MNRAS, Feb 2023

   ADS Bibcode: 2023MNRAS.519.3118W

   Abs DOI

   JWST is set to transform many areas of astronomy, one of the most exciting is the expansion of the redshift frontier to z \textgreater 10. In its first year, alone JWST should discover hundreds of galaxies, dwarfing the handful currently known. To prepare for these powerful observational constraints, we use the First Light And Reionization Epoch simulations (FLARES) to predict the physical and observational properties of the z \textgreater 10 population of galaxies accessible to JWST. This is the first time such predictions have been made using a hydrodynamical model validated at low redshift. Our predictions at z = 10 are broadly in agreement with current observational constraints on the far-UV luminosity function and UV continuum slope β, though the observational uncertainties are large. We note tension with recent constraints z ~ 13 from Harikane et al. (2021) - compared to these constraints, FLARES predicts objects with the same space density should have an order-of-magnitude lower luminosity, though this is mitigated slightly if dust attenuation is negligible in these systems. Our predictions suggest that in JWST’s first cycle alone, around 600 galaxies should be identified at z \textgreater 10, with the first small samples available at z \textgreater 13.

4. MNRAS

   First Light And Reionization Epoch Simulations (FLARES) VII: The star formation and metal enrichment histories of galaxies in the early Universe

   Stephen M. Wilkins, Aswin P. Vijayan, Christopher C. Lovell, and 8 more authors

   MNRAS, Jan 2023

   ADS Bibcode: 2023MNRAS.518.3935W

   Abs DOI

   The star formation and metal enrichment histories of galaxies - at any epoch - constitute one of the key properties of galaxies, and their measurement is a core aim of observational extragalactic astronomy. The lack of deep rest-frame optical coverage at high redshift has made robust constraints elusive, but this is now changing thanks to JWST. In preparation for the constraints provided by JWST, we explore the star formation and metal enrichment histories of galaxies at z = 5-13 using the First Light And Reionization Epoch Simulations (FLARES) suite. Built on the EAGLE model, the unique strategy of FLARES allows us to simulate galaxies with a wide range of stellar masses (and luminosities) and environments. While we predict significant redshift evolution of average ages and specific star formation rates, our core result is mostly a flat relationship of age and specific star formation rate with stellar mass. We also find that galaxies in this epoch predominantly have strongly rising star formation histories, albeit with the normalization dropping with redshift and stellar mass. In terms of chemical enrichment, we predict a strong stellar mass-metallicity relation present at z = 10 and beyond alongside significant α-enhancement. Finally, we find no large-scale environmental dependence of the relationship between age, specific star formation rate, or metallicity with stellar mass.

5. ICML

   A Hierarchy of Normalizing Flows for Modelling the Galaxy-Halo Relationship

   Christopher C. Lovell, Sultan Hassan, Daniel Anglés-Alcázar, and 8 more authors

   ICML, Jul 2023

   Publication Title: arXiv e-prints ADS Bibcode: 2023arXiv230706967L

   Abs DOI

   Using a large sample of galaxies taken from the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project, a suite of hydrodynamic simulations varying both cosmological and astrophysical parameters, we train a normalizing flow (NF) to map the probability of various galaxy and halo properties conditioned on astrophysical and cosmological parameters. By leveraging the learnt conditional relationships we can explore a wide range of interesting questions, whilst enabling simple marginalisation over nuisance parameters. We demonstrate how the model can be used as a generative model for arbitrary values of our conditional parameters; we generate halo masses and matched galaxy properties, and produce realisations of the halo mass function as well as a number of galaxy scaling relations and distribution functions. The model represents a unique and flexible approach to modelling the galaxy-halo relationship.

6. ApJ

   The JWST Hubble Sequence: The Rest-frame Optical Evolution of Galaxy Structure at 1.5 \textless z \textless 6.5

   Leonardo Ferreira, Christopher J. Conselice, Elizaveta Sazonova, and 13 more authors

   ApJ, Sep 2023

   Publisher: The American Astronomical Society

   Abs DOI

   We present results on the morphological and structural evolution of a total of 3956 galaxies observed with JWST at 1.5 \textless z \textless 6.5 in the JWST CEERS observations that overlap with the CANDELS EGS field. This is the biggest visually classified sample observed with JWST yet, ∼20 times larger than previous studies, and allows us to examine in detail how galaxy structure has changed over this critical epoch. All sources were classified by six individual classifiers using a simple classification scheme aimed at producing disk/spheroid/peculiar classifications, whereby we determine how the relative number of these morphologies has evolved since the Universe’s first billion years. Additionally, we explore structural and quantitative morphology measurements using Morfometryka, and show that galaxies with M * \textgreater 109 M ⊙ at z \textgreater 3 are not dominated by irregular and peculiar structures, either visually or quantitatively, as previously thought. We find a strong dominance of morphologically selected disk galaxies up to z = 6 in this mass range. We also find that the stellar mass and star formation rate densities are dominated by disk galaxies up to z ∼ 6, demonstrating that most stars in the Universe were likely formed in a disk galaxy. We compare our results to theory to show that the fraction of types we find is predicted by cosmological simulations, and that the Hubble Sequence was already in place as early as one billion years after the Big Bang. Additionally, we make our visual classifications public for the community.

7. MNRAS

   First light and reionisation epoch simulations (FLARES) - VIII. The emergence of passive galaxies at z ≥ 5

   Christopher C. Lovell, Will Roper, Aswin P. Vijayan, and 9 more authors

   MNRAS, Nov 2023

   ADS Bibcode: 2023MNRAS.525.5520L

   Abs DOI

   Passive galaxies are ubiquitous in the local universe, and various physical channels have been proposed that lead to this passivity. To date, robust passive galaxy candidates have been detected up to z ≤ 5, but it is still unknown if they exist at higher redshifts, what their relative abundances are, and what causes them to stop forming stars. We present predictions from the first light and reionisation epoch simulations (FLARES), a series of zoom simulations of a range of overdensities using the EAGLE code. Passive galaxies occur naturally in the EAGLE model at high redshift, and are in good agreement with number density estimates from Hubble Space Telescope (HST) and early JWST results at 3 ≤ z ≤ 5. Due to the unique FLARES approach, we extend these predictions to higher redshifts, finding passive galaxy populations up to z ~ 8. Feedback from supermassive black holes is the main driver of passivity, leading to reduced gas fractions and star forming gas reservoirs. We find that passive galaxies at z ≥ 5 are not identified in the typical UVJ selection space due to their still relatively young stellar populations, and present new rest-frame selection regions. We also produce mock NIRCam and MIRI fluxes, and find that significant numbers of passive galaxies at z ≥ 5 should be detectable in upcoming wide surveys with JWST. Finally, we present JWST colour distributions, with new selection regions in the observer-frame for identifying these early passive populations.

8. arXiv

   Cosmic Evolution Early Release Science (CEERS) survey: The colour evolution of galaxies in the distant Universe

   Stephen M. Wilkins, Jack C. Turner, Micaela B. Bagley, and 20 more authors

   Nov 2023

   Publication Title: arXiv e-prints ADS Bibcode: 2023arXiv231108065W

   Abs

   The wavelength-coverage and sensitivity of JWST now enables us to probe the rest-frame UV - optical spectral energy distributions (SEDs) of galaxies at high-redshift (\z\textgreater4\). From these SEDs it is, in principle, through SED fitting possible to infer key physical properties, including stellar masses, star formation rates, and dust attenuation. These in turn can be compared with the predictions of galaxy formation simulations allowing us to validate and refine the incorporated physics. However, the inference of physical properties, particularly from photometry alone, can lead to large uncertainties and potential biases. Instead, it is now possible, and common, for simulations to be }emph{forward-modelled} to yield synthetic observations that can be compared directly to real observations. In this work, we measure the JWST broadband fluxes and colours of a robust sample of \58 the distributions differ somewhat, though our observed sample size is small and thus susceptible to statistical fluctuations. Likewise, the predicted and observed colour evolution show broad agreement, at least at \58 though, again, the sample size is small here.

9. MNRAS

   First light and reionization epoch simulations (FLARES) X III: the lyman-continuum emission of high-redshift galaxies

   Louise T. C. Seeyave, Stephen M. Wilkins, Jussi K. Kuusisto, and 10 more authors

   MNRAS, Oct 2023

   ADS Bibcode: 2023MNRAS.525.2422S

   Abs DOI

   The history of reionization is highly dependent on the ionizing properties of high-redshift galaxies. It is therefore important to have a solid understanding of how the ionizing properties of galaxies are linked to physical and observable quantities. In this paper, we use the First Light and Reionization Epoch Simulations (FLARES) to study the Lyman-continuum (LyC, i.e. hydrogen-ionizing) emission of massive (\M_* 10^8}, }mathrm{M_}odot }\) galaxies at redshifts z = 5 - 10. We find that the specific ionizing emissivity (i.e. intrinsic ionizing emissivity per unit stellar mass) decreases as stellar mass increases, due to the combined effects of increasing age and metallicity. FLARES predicts a median ionizing photon production efficiency (i.e. intrinsic ionizing emissivity per unit intrinsic far-UV luminosity) of {}log _{10}(}xi _{}rm ion}}rm {/erg^{-1}Hz})=25.40^{+0.16}_{-0.17} with values spanning the range {}log _{10}(}xi _{}rm ion}}rm {/erg^{-1}Hz})=25-25.75\. This is within the range of many observational estimates, but below some of the extremes observed. We compare the production efficiency with observable properties, and find a weak negative correlation with the UV-continuum slope, and a positive correlation with the [O III] equivalent width. We also consider the dust-attenuated production efficiency (i.e. intrinsic ionizing emissivity per unit dust-attenuated far-UV luminosity), and find a median of {}log _{10}(}xi _{}rm ion}}rm {/erg^{-1}Hz})}sim 25.5\. Within our sample of \M_* 10^8}, }mathrm{M_}odot } galaxies, it is the stellar populations in low mass galaxies that contribute the most to the total ionizing emissivity. Active galactic nuclei (AGN) emission accounts for 10 - 20 per cent of the total emissivity at a given redshift, and extends the LyC luminosity function by ~0.5 dex.

10. MNRAS

    First light and reionization epoch simulations (FLARES) X: environmental galaxy bias and survey variance at high redshift

    Peter A. Thomas, Christopher C. Lovell, Maxwell G. A. Maltz, and 5 more authors

    MNRAS, Sep 2023

    ADS Bibcode: 2023MNRAS.524...43T

    Abs DOI

    Upcoming deep galaxy surveys with JWST will probe galaxy evolution during the epoch of reionization (EoR, 5 ≤ z ≤ 10) over relatively compact areas (e.g. ~300 arcmin2 for the JADES GTO survey). It is therefore imperative that we understand the degree of survey variance to evaluate how representative the galaxy populations in these studies will be. We use the First Light And Reionization Epoch Simulations (FLARES) to measure the galaxy bias of various tracers over an unprecedentedly large range in overdensity for a hydrodynamic simulation, and use these relations to assess the impact of bias and clustering on survey variance in the EoR. Star formation is highly biased relative to the underlying dark matter distribution, with the mean ratio of the stellar to dark matter density varying by a factor of 100 between regions of low and high matter overdensity (smoothed on a scale of 14 h-1 cMpc). This is reflected in the galaxy distribution - the most massive galaxies are found solely in regions of high overdensity. As a consequence of the above, galaxies in the EoR are highly clustered, which can lead to a large variance in survey number counts. For mean number counts N ≲ 100 (1000), in a unit redshift slice of angular area 300 arcmin2 (1.4 deg2), the 2σ range in N is roughly a factor of four (two). We present relations between the expected variance and survey area for different survey geometries; these relations will be of use to observers wishing to understand the impact of survey variance on their results.

11. MNRAS

    First light and reionization epoch simulations (FLARES) XI: [O III] emitting galaxies at 5 \textless z \textless 10

    Stephen M. Wilkins, Christopher C. Lovell, Aswin P. Vijayan, and 12 more authors

    MNRAS, Jul 2023

    ADS Bibcode: 2023MNRAS.522.4014W

    Abs DOI

    JWST has now made it possible to probe the rest-frame optical line emission of high-redshift galaxies extending to z ≈ 9, and potentially beyond. To aid in the interpretation of these emerging constraints, in this work we explore predictions for [O III]λλ4960, 5008 Å emission in high-redshift galaxies using the First Light and Reionization Epoch Simulations (FLARES). We produce predictions for the [O III] luminosity function, its correlation with the UV luminosity, and the distribution of equivalent widths (EWs). We also explore how the [O III] EW correlates with physical properties including specific star formation rate, metallicity, and dust attenuation. Our predictions are largely consistent with recent observational constraints on the luminosity function, average EWs, and line ratios. However, they fail to reproduce the observed tail of high-EW sources and the number density of extreme line emitters. Possibilities to explain these discrepancies include an additional source of ionizing photons and/or greater stochasticity in star formation in the model or photometric scatter and/or bias in the observations. With JWST now rapidly building larger samples and a wider range of emission lines the answer to this remaining discrepancy should be available imminently.

12. ApJ

    JWST Constraints on the UV Luminosity Density at Cosmic Dawn: Implications for 21 cm Cosmology

    Sultan Hassan, Christopher C. Lovell, Piero Madau, and 10 more authors

    ApJ, Nov 2023

    Publisher: IOP ADS Bibcode: 2023ApJ...958L...3H

    Abs DOI

    An unprecedented array of new observational capabilities are starting to yield key constraints on models of the epoch of first light in the Universe. In this Letter we discuss the implications of the UV radiation background at cosmic dawn inferred by recent JWST observations for radio experiments aimed at detecting the redshifted 21 cm hyperfine transition of diffuse neutral hydrogen. Under the basic assumption that the 21 cm signal is activated by the Lyα photon field produced by metal-poor stellar systems, we show that a detection at the low frequencies of the EDGES and SARAS3 experiments may be expected from a simple extrapolation of the declining UV luminosity density inferred at z ≲ 14 from JWST early galaxy data. Accounting for an early radiation excess above the cosmic microwave background suggests a shallower or flat evolution to simultaneously reproduce low- and high-z current UV luminosity density constraints, which cannot be entirely ruled out, given the large uncertainties from cosmic variance and the faint-end slope of the galaxy luminosity function at cosmic dawn. Our findings raise the intriguing possibility that a high star formation efficiency at early times may trigger the onset of intense Lyα emission at redshift z ≲ 20 and produce a cosmic 21 cm absorption signal 200 Myr after the Big Bang.

13. ApJ

    Robust Field-level Likelihood-free Inference with Galaxies

    Natalí S. M. Santi, Helen Shao, Francisco Villaescusa-Navarro, and 12 more authors

    ApJ, Jul 2023

    Publisher: IOP ADS Bibcode: 2023ApJ...952...69D

    Abs DOI

    We train graph neural networks to perform field-level likelihood-free inference using galaxy catalogs from state-of-the-art hydrodynamic simulations of the CAMELS project. Our models are rotational, translational, and permutation invariant and do not impose any cut on scale. From galaxy catalogs that only contain 3D positions and radial velocities of ~1000 galaxies in tiny \{(25},{h}^{-1}}mathrm{Mpc})}^{3} volumes our models can infer the value of Ωm with approximately 12% precision. More importantly, by testing the models on galaxy catalogs from thousands of hydrodynamic simulations, each having a different efficiency of supernova and active galactic nucleus feedback, run with five different codes and subgrid models-IllustrisTNG, SIMBA, Astrid, Magneticum, SWIFT-EAGLE-we find that our models are robust to changes in astrophysics, subgrid physics, and subhalo/galaxy finder. Furthermore, we test our models on 1024 simulations that cover a vast region in parameter space-variations in five cosmological and 23 astrophysical parameters-finding that the model extrapolates really well. Our results indicate that the key to building a robust model is the use of both galaxy positions and velocities, suggesting that the network has likely learned an underlying physical relation that does not depend on galaxy formation and is valid on scales larger than ~10 h -1 kpc.

14. A&A

    ALMACAL. XI. Over-densities as signposts for proto-clusters? A cautionary tale

    Jianhang Chen, R. J. Ivison, Martin A. Zwaan, and 6 more authors

    A&A, Jul 2023

    ADS Bibcode: 2023A&A...675L..10C

    Abs DOI

    It may be unsurprising that the most common approach to finding proto-clusters is to search for over-densities of galaxies. Upgrades to submillimetre (submm) interferometers and the advent of the James Webb Space Telescope will soon offer the opportunity to find more distant candidate proto-clusters in deep sky surveys without any spectroscopic confirmation. In this Letter, we report the serendipitous discovery of an extremely dense region centred on the blazar, J0217−0820, at z = 0.6 in the ALMACAL sky survey. Its density is eight times higher than that predicted by blind submm surveys. Among the seven submm-bright galaxies, three are as bright as conventional single-dish submm galaxies, with S870 μm \textgreater 3 mJy. The over-density is thus comparable to the densest known and confirmed proto-cluster cores. However, their spectra betray a wide range of redshifts. We investigate the likelihood of line-of-sight projection effects using light cones from cosmological simulations, finding that the deeper we search, the higher the chance that we will suffer from such projection effects. The extreme over-density around J0217−0820 demonstrates the strong cosmic variance we may encounter in the deep submm surveys. Thus, we should also question the fidelity of galaxy proto-cluster candidates selected via over-densities of galaxies, where the negative K correction eases the detection of dusty galaxies along an extraordinarily extended line of sight.

15. arXiv

    Field-level simulation-based inference with galaxy catalogs: the impact of systematic effects

    Natalí S. M. Santi, Francisco Villaescusa-Navarro, L. Raul Abramo, and 11 more authors

    Oct 2023

    Publication Title: arXiv e-prints ADS Bibcode: 2023arXiv231015234D

    Abs DOI

    It has been recently shown that a powerful way to constrain cosmological parameters from galaxy redshift surveys is to train graph neural networks to perform field-level likelihood-free inference without imposing cuts on scale. In particular, de Santi et al. (2023) developed models that could accurately infer the value of {}Omega_{}rm m} from catalogs that only contain the positions and radial velocities of galaxies that are robust to uncertainties in astrophysics and subgrid models. However, observations are affected by many effects, including 1) masking, 2) uncertainties in peculiar velocities and radial distances, and 3) different galaxy selections. Moreover, observations only allow us to measure redshift, intertwining galaxies’ radial positions and velocities. In this paper we train and test our models on galaxy catalogs, created from thousands of state-of-the-art hydrodynamic simulations run with different codes from the CAMELS project, that incorporate these observational effects. We find that, although the presence of these effects degrades the precision and accuracy of the models, and increases the fraction of catalogs where the model breaks down, the fraction of galaxy catalogs where the model performs well is over 90 %, demonstrating the potential of these models to constrain cosmological parameters even when applied to real data.

16. ApJ

    A Universal Equation to Predict Ωm from Halo and Galaxy Catalogs

    Helen Shao, Natalí S. M. Santi, Francisco Villaescusa-Navarro, and 14 more authors

    ApJ, Oct 2023

    Publisher: IOP ADS Bibcode: 2023ApJ...956..149S

    Abs DOI

    We discover analytic equations that can infer the value of Ωm from the positions and velocity moduli of halo and galaxy catalogs. The equations are derived by combining a tailored graph neural network (GNN) architecture with symbolic regression. We first train the GNN on dark matter halos from Gadget N-body simulations to perform field-level likelihood-free inference, and show that our model can infer Ωm with ~6% accuracy from halo catalogs of thousands of N-body simulations run with six different codes: Abacus, CUBEP3M, Gadget, Enzo, PKDGrav3, and Ramses. By applying symbolic regression to the different parts comprising the GNN, we derive equations that can predict Ωm from halo catalogs of simulations run with all of the above codes with accuracies similar to those of the GNN. We show that, by tuning a single free parameter, our equations can also infer the value of Ωm from galaxy catalogs of thousands of state-of-the-art hydrodynamic simulations of the CAMELS project, each with a different astrophysics model, run with five distinct codes that employ different subgrid physics: IllustrisTNG, SIMBA, Astrid, Magneticum, SWIFT-EAGLE. Furthermore, the equations also perform well when tested on galaxy catalogs from simulations covering a vast region in parameter space that samples variations in 5 cosmological and 23 astrophysical parameters. We speculate that the equations may reflect the existence of a fundamental physics relation between the phase-space distribution of generic tracers and Ωm, one that is not affected by galaxy formation physics down to scales as small as 10 h -1 kpc.

17. MNRAS

    First light and reionization epoch simulations (FLARES) IX: the physical mechanisms driving compact galaxy formation and evolution

    William J. Roper, Christopher C. Lovell, Aswin P. Vijayan, and 6 more authors

    MNRAS, Dec 2023

    Publisher: OUP ADS Bibcode: 2023MNRAS.526.6128R

    Abs DOI

    In the First Light And Reionization Epoch Simulations (FLARES) suite of hydrodynamical simulations, we find the high-redshift (z \textgreater 5) intrinsic size-luminosity relation is, surprisingly, negatively sloped. However, after including the effects of dust attenuation, we find a positively sloped UV observed size-luminosity relation in good agreement with other simulated and observational studies. In this work, we extend this analysis to probe the underlying physical mechanisms driving the formation and evolution of the compact galaxies driving the negative size-mass/size-luminosity relation. We find the majority of compact galaxies (R1/2, ⋆ \textless 1 pkpc, which drive the negative slope of the size-mass relation, have transitioned from extended to compact sizes via efficient centralized cooling, resulting in high specific star formation rates in their cores. These compact stellar systems are enshrouded by non-star-forming gas distributions as much as 100 times larger than their stellar counterparts. By comparing with galaxies from the EAGLE simulation suite, we find that these extended gas distributions ’turn on’ and begin to form stars between z = 5 and 0 leading to increasing sizes, and thus the evolution of the size-mass relation from a negative to a positive slope. This explicitly demonstrates the process of inside-out galaxy formation in which compact bulges form earlier than the surrounding discs.

18. MNRAS

    Mapping circumgalactic medium observations to theory using machine learning

    Sarah Appleby, Romeel Davé, Daniele Sorini, and 2 more authors

    MNRAS, Oct 2023

    Publisher: OUP ADS Bibcode: 2023MNRAS.525.1167A

    Abs DOI

    We present a random forest (RF) framework for predicting circumgalactic medium (CGM) physical conditions from quasar absorption line observables, trained on a sample of Voigt profile-fit synthetic absorbers from the SIMBA cosmological simulation. Traditionally, extracting physical conditions from CGM absorber observations involves simplifying assumptions such as uniform single-phase clouds, but by using a cosmological simulation we bypass such assumptions to better capture the complex relationship between CGM observables and underlying gas conditions. We train RF models on synthetic spectra for H I and selected metal lines around galaxies across a range of star formation rates, stellar masses, and impact parameters, to predict absorber overdensities, temperatures, and metallicities. The models reproduce the true values from SIMBA well, with normalized transverse standard deviations of 0.50-0.54 dex in overdensity, 0.32-0.54 dex in temperature, and 0.49-0.53 dex in metallicity predicted from metal lines (not H I), across all ions. Examining the feature importance, the RF indicates that the overdensity is most informed by the absorber column density, the temperature is driven by the line width, and the metallicity is most sensitive to the specific star formation rate. Alternatively examining feature importance by removing one observable at a time, the overdensity and metallicity appear to be more driven by the impact parameter. We introduce a normalizing flow approach in order to ensure the scatter in the true physical conditions is accurately spanned by the network. The trained models are available online.

19. MNRAS

    Seeing sharper and deeper: JWST’s first glimpse of the photometric and spectroscopic properties of galaxies in the epoch of reionization

    James A. A. Trussler , Nathan J. Adams, Christopher J. Conselice, and 12 more authors

    MNRAS, Aug 2023

    Publisher: OUP ADS Bibcode: 2023MNRAS.523.3423T

    Abs DOI

    We analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionization (EoR) within the SMACS J0723.3-7327 JWST Early Release Observations field. Given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using NIRCam photometry alone, finding that F115W imaging is essential to distinguish between z ~ 8 galaxies with high equivalent width (EW) [O III] λ5007 emission and z ~ 10 Balmer break galaxies. We find that all four sources exhibit strong (≥0.6 mag) F356W-F444W colours, which sit at the extreme end of theoretical predictions from numerical simulations. We find that these galaxies deviate (by ≈0.5 dex) from the local correlation between [O III] λ5007/H β and [Ne III] λ3869/[O II], which is consistent with the predictions from simulations of high-redshift galaxies having elevated line-excitation ratios. We measure the [O III] λ5007 rest-frame EWs both directly from the spectroscopy, and indirectly as inferred from the strong F356W-F444W colours, finding large [O III] λ5007 EWs of 225-1740 Å. The [O III] λ5007 and H β EWs are consistent with those seen in extreme, intensely star-forming dwarf galaxies in the local Universe. Our structural analysis indicates that these galaxies are resolved, exhibiting irregular shapes with bright clumps. In line with the predictions from the FLARES hydrodynamic simulations, such intense star formation and extreme nebular conditions are likely the norm, rather than the exception, in the EoR.

2022

1. MNRAS

   A machine learning approach to mapping baryons on to dark matter haloes using the EAGLE and C-EAGLE simulations

   Christopher C. Lovell, Stephen M. Wilkins, Peter A. Thomas, and 4 more authors

   MNRAS, Feb 2022

   ADS Bibcode: 2022MNRAS.509.5046L

   Abs DOI

   High-resolution cosmological hydrodynamic simulations are currently limited to relatively small volumes due to their computational expense. However, much larger volumes are required to probe rare, overdense environments, and measure clustering statistics of the large-scale structure. Typically, zoom simulations of individual regions are used to study rare environments, and semi-analytic models and halo occupation models applied to dark-matter-only (DMO) simulations are used to study the Universe in the large-volume regime. We propose a new approach, using a machine learning framework, to explore the halo-galaxy relationship in the periodic EAGLE simulations, and zoom C-EAGLE simulations of galaxy clusters. We train a tree-based machine learning method to predict the baryonic properties of galaxies based on their host dark matter halo properties. The trained model successfully reproduces a number of key distribution functions for an infinitesimal fraction of the computational cost of a full hydrodynamic simulation. By training on both periodic simulations and zooms of overdense environments, we learn the bias of galaxy evolution in differing environments. This allows us to apply the trained model to a larger DMO volume than would be possible if we only trained on a periodic simulation. We demonstrate this application using the (800 Mpc)3 P-Millennium simulation, and present predictions for key baryonic distribution functions and clustering statistics from the EAGLE model in this large volume.

2. MNRAS

   First Light And Reionisation Epoch Simulations (FLARES) III: The properties of massive dusty galaxies at cosmic dawn

   Aswin P. Vijayan, Stephen M. Wilkins, Christopher C. Lovell, and 6 more authors

   MNRAS, Feb 2022

   ADS Bibcode: 2022MNRAS.tmp..355V

   Abs DOI

   Using the First Light And Reionisation Epoch Simulations (FLARES) we explore the dust driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing the galaxy sample using the radiative transfer code SKIRT we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX-β relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but under-predict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the FLARES IRX-β relation (for 5 ≤ z ≤ 8) predominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end (~1010 M⊙) and shows no evolution in the median normalization with redshift. We also look at the dependence of the peak dust temperature (Tpeak) on various galaxy properties including the stellar mass, IR luminosity and sSFR, finding the correlation to be strongest with sSFR. The luminosity-weighted dust temperatures increase towards higher redshifts, with the slope of the Tpeak - redshift relation showing a higher slope than the lower redshift relations obtained from previous observational and theoretical works. The results from FLARES, which is able to provide a better statistical sample of high-redshift galaxies compared to other simulations, provides a distinct vantage point for the high-redshift Universe.

3. ApJ

   The BPT Diagram in Cosmological Galaxy Formation Simulations: Understanding the Physics Driving Offsets at High Redshift

   Prerak Garg, Desika Narayanan, Nell Byler, and 9 more authors

   ApJ, Feb 2022

   ADS Bibcode: 2022ApJ...926...80G

   Abs DOI

   The Baldwin, Philips, & Terlevich diagram of [O III]/Hβ versus [N II]/Hα (hereafter N2-BPT) has long been used as a tool for classifying galaxies based on the dominant source of ionizing radiation. Recent observations have demonstrated that galaxies at z ~ 2 reside offset from local galaxies in the N2-BPT space. In this paper, we conduct a series of controlled numerical experiments to understand the potential physical processes driving this offset. We model nebular line emission in a large sample of galaxies, taken from the SIMBA cosmological hydrodynamic galaxy formation simulation, using the CLOUDY photoionization code to compute the nebular line luminosities from H II regions. We find that the observed shift toward higher [O III]/Hβ and [N II]/Hα values at high redshift arises from sample selection: when we consider only the most massive galaxies M * ~ 1010-11 M ⊙, the offset naturally appears, due to their high metallicities. We predict that deeper observations that probe lower-mass galaxies will reveal galaxies that lie on a locus comparable to z ~ 0 observations. Even when accounting for samples-selection effects, we find that there is a subtle mismatch between simulations and observations. To resolve this discrepancy, we investigate the impact of varying ionization parameters, H II region densities, gas-phase abundance patterns, and increasing radiation field hardness on N2-BPT diagrams. We find that either decreasing the ionization parameter or increasing the N/O ratio of galaxies at fixed O/H can move galaxies along a self-similar arc in N2-BPT space that is occupied by high-redshift galaxies.

4. MNRAS

   First Light And Reionisation Epoch Simulations (FLARES) - IV. The size evolution of galaxies at z ≥ 5

   William J. Roper, Christopher C. Lovell, Aswin P. Vijayan, and 5 more authors

   MNRAS, Aug 2022

   ADS Bibcode: 2022MNRAS.514.1921R

   Abs DOI

   We present the intrinsic and observed sizes of galaxies at z ≥ 5 in the First Light And Reionisation Epoch Simulations (FLARES). We employ the large effective volume of FLARES to produce a sizeable sample of high-redshift galaxies with intrinsic and observed luminosities and half-light radii in a range of rest-frame ultraviolet (UV) and visual photometric bands. This sample contains a significant number of intrinsically ultracompact galaxies in the far-UV (1500 Å), leading to a negative intrinsic far-UV size-luminosity relation. However, after the inclusion of the effects of dust these same compact galaxies exhibit observed sizes that are as much as 50 times larger than those measured from the intrinsic emission, and broadly agree with a range of observational samples. This increase in size is driven by the concentration of dust in the core of galaxies, heavily attenuating the intrinsically brightest regions. At fixed luminosity we find a galaxy size redshift evolution with a slope of m = 1.21-1.87 depending on the luminosity sample in question, and we demonstrate the wavelength dependence of the size-luminosity relation that will soon be probed by the James Webb Space Telescope.

5. MNRAS

   First Light and Reionisation Epoch Simulations (FLARES) - VI. The colour evolution of galaxies z = 5-15

   Stephen M. Wilkins, Aswin P. Vijayan, Christopher C. Lovell, and 6 more authors

   MNRAS, Dec 2022

   ADS Bibcode: 2022MNRAS.517.3227W

   Abs DOI

   With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope (JWST) is poised to revolutionize our view of the distant, high-redshift (z \textgreater 5) Universe. While Webb’s spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant objects and providing more comprehensive samples than accessible to spectroscopy alone. In addition to identifying objects, photometric observations can also be used to infer physical properties and thus be used to constrain galaxy formation models. However, inferred physical properties from broad-band photometric observations, particularly in the absence of spectroscopic redshifts, often have large uncertainties. With the development of new tools for forward modelling simulations, it is now routinely possible to predict observational quantities, enabling a direct comparison with observations. With this in mind, in this work, we make predictions for the colour evolution of galaxies at z = 5-15 using the First Light And Reionisation Epoch Simulations (FLARES) cosmological hydrodynamical simulation suite. We predict a complex evolution with time, driven predominantly by strong nebular line emission passing through individual bands. These predictions are in good agreement with existing constraints from Hubble and Spitzer as well as some of the first results from Webb. We also contrast our predictions with other models in the literature: While the general trends are similar, we find key differences, particularly in the strength of features associated with strong nebular line emission. This suggests photometric observations alone should provide useful discriminating power between different models and physical states of galaxies.

6. MNRAS

   An orientation bias in observations of submillimetre galaxies

   C. C. Lovell, J. E. Geach, R. Davé, and 5 more authors

   MNRAS, Sep 2022

   ADS Bibcode: 2022MNRAS.515.3644L

   Abs DOI

   Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an ’orientation bias’ in the selection and analysis of such galaxies in flux-limited cosmological surveys? We investigated these questions using the SIMBA cosmological simulation paired with the dust radiative transfer code POWDERDAY. We selected eight simulated SMGs (S850 ≳ 2 mJy) at z = 2, and measured the variance of their ’observed’ emission over 50 random orientations. Each galaxy exhibits significant scatter in its emission close to the peak of the thermal dust emission, with variation in flux density of up to a factor of 2.7. This results in an appreciable dispersion in the inferred dust temperatures and infrared luminosities (16th-84th percentile ranges of 5 K and 0.1 dex, respectively) and therefore a fundamental uncertainty in derived parameters such as dust mass and star formation rate (~30 per cent for the latter using simple calibrations). Using a Monte Carlo simulation we also assessed the impact of orientation on flux-limited surveys, finding a bias in the selection of SMGs towards those with face-on orientations, as well as those at lower redshifts. We predict that the orientation bias will affect flux-limited single-dish surveys, most significantly at THz frequencies, and this bias should be taken into account when placing the results of targeted follow-up studies in a statistical context.

7. MNRAS

   MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star forming galaxies and active galactic nuclei

   C. L. Hale, I. H. Whittam, M. J. Jarvis, and 23 more authors

   MNRAS, Nov 2022

   ADS Bibcode: 2022MNRAS.tmp.3133H

   Abs DOI

   We present deep 1.4 GHz source counts from ~5 deg2 of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to S1.4GHz ~15 μJy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25 per cent contribution to the total sky background temperature (Tb ~100 mK) at ~15 μJy.

8. ApJ

   Chaotic and Clumpy Galaxy Formation in an Extremely Massive Reionization-era Halo

   Justin S. Spilker, Christopher C. Hayward, Daniel P. Marrone, and 20 more authors

   ApJ, Apr 2022

   ADS Bibcode: 2022ApJ...929L...3S

   Abs DOI

   The SPT 0311-58 system at z = 6.900 is an extremely massive structure within the reionization epoch and offers a chance to understand the formation of galaxies at an extreme peak in the primordial density field. We present 70 mas Atacama Large Millimeter/submillimeter Array observations of the dust continuum and [C II] 158 μm emission in the central pair of galaxies and reach physical resolutions of ~100-350 pc, among the most detailed views of any reionization-era system to date. The observations resolve the source into at least a dozen kiloparsec-size clumps. The global kinematics and high turbulent velocity dispersion within the galaxies present a striking contrast to recent claims of dynamically cold thin-disk kinematics in some dusty galaxies just 800 Myr later at z ~ 4. We speculate that both gravitational interactions and fragmentation from massive parent disks have likely played a role in the overall dynamics and formation of clumps in the system. Each clump individually is comparable in mass to other 6 \textless z \textless 8 galaxies identified in rest-UV/optical deep field surveys, but with star formation rates elevated by a factor of ~3-5. Internally, the clumps themselves bear close resemblance to greatly scaled-up versions of virialized cloud-scale structures identified in low-redshift galaxies. Our observations are qualitatively similar to the chaotic and clumpy assembly within massive halos seen in simulations of high-redshift galaxies.

2021

1. MNRAS

   Reproducing submillimetre galaxy number counts with cosmological hydrodynamic simulations

   Christopher C. Lovell, James E. Geach, Romeel Davé, and 2 more authors

   MNRAS, Mar 2021

   Abs DOI

   Matching the number counts of high-z submillimetre-selected galaxies (SMGs) has been a long-standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to model the submm emission from galaxies in the SIMBA cosmological hydrodynamic simulations, and compare predictions to the latest single-dish observational constraints on the abundance of 850 μm-selected sources. We find good agreement with the shape of the integrated 850 μm luminosity function, and the normalization is within 0.25 dex at \textgreater3 mJy, unprecedented for a fully cosmological hydrodynamic simulation, along with good agreement in the redshift distribution of bright SMGs. The agreement is driven primarily by SIMBA’s good match to infrared measures of the star formation rate (SFR) function between z = 2 and 4 at high SFRs. Also important is the self-consistent on-the-fly dust model in SIMBA, which predicts, on average, higher dust masses (by up to a factor of 2.5) compared to using a fixed dust-to-metals ratio of 0.3. We construct a light-cone to investigate the effect of far-field blending, and find that 52 per cent of sources are blends of multiple components, which makes a small contribution to the normalization of the bright end of the number counts. We provide new fits to the 850 μm luminosity as a function of SFR and dust mass. Our results demonstrate that solutions to the discrepancy between submm counts in simulations and observations, such as a top-heavy initial mass function, are unnecessary, and that submillimetre-bright phases are a natural consequence of massive galaxy evolution.

2. ApJS

   powderday: Dust Radiative Transfer for Galaxy Simulations

   Desika Narayanan, Matthew J. Turk, Thomas Robitaille, and 18 more authors

   ApJS, Jan 2021

   Publisher: American Astronomical Society

   Abs DOI

   We present powderday (available at https://github.com/dnarayanan/powderday), a flexible, fast, open-source dust radiative transfer package designed to interface with both idealized and cosmological galaxy formation simulations. powderday builds on fsps stellar population synthesis models, and hyperion dust radiative transfer, and employs yt to interface between different software packages. We include our stellar population synthesis modeling on the fly, allowing significant flexibility in the assumed stellar physics and nebular line emission. The dust content follows either simple observationally motivated prescriptions (i.e., constant dust-to-metals ratios, or dust-to-gas ratios that vary with metallicity), direct modeling from galaxy formation simulations that include dust physics, as well as a novel approach that includes the dust content via learning-based algorithms from the simba cosmological galaxy formation simulation. Active galactic nuclei (AGNs) can additionally be included via a range of prescriptions. The output of these models are broadband (912 Å–1 mm) spectral energy distributions (SEDs), as well as filter-convolved monochromatic images. powderday is designed to eliminate last-mile efforts by researchers that employ different hydrodynamic galaxy formation models and seamlessly interfaces with gizmo, arepo, gasoline, changa, and enzo. We demonstrate the capabilities of the code via three applications: a model for the star formation rate–infrared luminosity relation in galaxies (including the impact of AGNs), the impact of circumstellar dust around AGB stars on the mid-infrared emission from galaxy SEDs, and the impact of galaxy inclination angle on dust attenuation laws.

3. MNRAS

   First Light And Reionization Epoch Simulations (FLARES) - I. Environmental dependence of high-redshift galaxy evolution

   Christopher C. Lovell, Aswin P. Vijayan, Peter A. Thomas, and 4 more authors

   MNRAS, Jan 2021

   Abs DOI

   We introduce the First Light And Reionisation Epoch Simulations (FLARES), a suite of zoom simulations using the EAGLE model. We resimulate a range of overdensities during the Epoch of Reionization (EoR) in order to build composite distribution functions, as well as explore the environmental dependence of galaxy formation and evolution during this critical period of galaxy assembly. The regions are selected from a large \(3.2 }, }mathrm{cGpc})^{3} parent volume, based on their overdensity within a sphere of radius 14 h-1 cMpc. We then resimulate with full hydrodynamics, and employ a novel weighting scheme that allows the construction of composite distribution functions that are representative of the full parent volume. This significantly extends the dynamic range compared to smaller volume periodic simulations. We present an analysis of the galaxy stellar mass function (GSMF), the star formation rate distribution function (SFRF), and the star-forming sequence (SFS) predicted by FLARES, and compare to a number of observational and model constraints. We also analyse the environmental dependence over an unprecedented range of overdensity. Both the GSMF and the SFRF exhibit a clear double-Schechter form, up to the highest redshifts (z = 10). We also find no environmental dependence of the SFS normalization. The increased dynamic range probed by FLARES will allow us to make predictions for a number of large area surveys that will probe the EoR in coming years, carried out on new observatories such as Roman and Euclid.

4. A&A

   The emergence of passive galaxies in the early Universe

   P. Santini, M. Castellano, E. Merlin, and 10 more authors

   A&A, Aug 2021

   Abs DOI

   The emergence of passive galaxies in the early Universe results from the delicate interplay among the different physical processes responsible for their rapid assembly and the abrupt shut-down of their star formation activity. Investigating the individual properties and demographics of early passive galaxies improves our understanding of these mechanisms. In this work we present a follow-up analysis of the z > 3 passive galaxy candidates selected by Merlin et al. (2019, MNRAS, 490, 3309) in the CANDELS fields. We begin by first confirming the accuracy of their passive classification by exploiting their sub-millimetre emission to demonstrate the lack of ongoing star formation. Using archival ALMA observations we are able to confirm at least 61% of the observed candidates as passive. While the remainder lack sufficiently deep data for confirmation, we are able to validate the entire sample in a statistical sense. We then estimate the stellar mass function (SMF) of all 101 passive candidates in three redshift bins from z = 5 to z = 3. We adopt a stepwise approach that has the advantage of taking into account photometric errors, mass and selection completeness issues, as well as the Eddington bias, without any a posteriori correction. We observe a pronounced evolution in the SMF around z ∼ 4, indicating that we are witnessing the emergence of the passive population at this epoch. Massive (M > 10\textlessSUP\textgreater11\textless/SUP\textgreater M\textlessSUB\textgreater⊙\textless/SUB\textgreater) passive galaxies, only accounting for a small (< 10%) fraction of galaxies at z > 4, become dominant at later epochs. Thanks to a combination of photometric quality, sample selection, and methodology, we overall find a higher density of passive galaxies than in previous works. The comparison with theoretical predictions, despite a qualitative agreement (at least for some of the models considered), denotes a still incomplete understanding of the physical processes responsible for the formation of these galaxies. Finally, we extrapolate our results to predict the number of early passive galaxies expected in surveys carried out with future facilities.

5. A&C

   Sengi: A small, fast, interactive viewer for spectral outputs from stellar population synthesis models

   C. C. Lovell

   A&C, Jan 2021

   Abs DOI

   We present Sengi, (https://christopherlovell.github.io/sengi), an online tool for viewing the spectral outputs of stellar population synthesis (SPS) codes. Typical SPS codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. This makes it difficult to present their results in an interactive, web-friendly format. Sengi uses Non-negative Matrix Factorisation (NMF) and bilinear interpolation to estimate output spectra for arbitrary values of stellar age and metallicity. The reduced disk requirements and computational expense allows the result to be served as a client-based Javascript application. In this paper we present the method for generating grids of spectra, fitting those grids with NMF, bilinear interpolation across the fitted coefficients, and finally provide estimates of the prediction and interpolation errors.

6. ApJ

   Cosmic Evolution of the H2 Mass Density and the Epoch of Molecular Gas

   T. K. Garratt, K. E. K. Coppin, J. E. Geach, and 13 more authors

   ApJ, May 2021

   Publisher: American Astronomical Society

   Abs DOI

   We present new empirical constraints on the evolution of , the cosmological mass density of molecular hydrogen, back to z ≈ 2.5. We employ a statistical approach measuring the average observed 850 μm flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the 850 μm band probes the Rayleigh–Jeans tail of thermal dust emission in the rest frame, and can therefore be used as an estimate of the mass of the interstellar medium. Our sample comprises of ≈150,000 galaxies in the UK InfraRed Telescope Infrared Deep Sky Survey Ultra-Deep Survey field with near-infrared magnitudes K AB ≤ 25 mag and photometric redshifts with corresponding probability distribution functions derived from deep 12-band photometry. With a sample approximately 2 orders of magnitude larger than in previous works we significantly reduce statistical uncertainties on to z ≈ 2.5. Our measurements are in broad agreement with recent direct estimates from blank field molecular gas surveys, finding that the epoch of molecular gas coincides with the peak epoch of star formation with at z ≈ 2. We demonstrate that can be broadly modeled by inverting the star formation rate (SFR) density with a fixed or weakly evolving star formation efficiency. This “constant efficiency” model shows a similar evolution to our statistically derived , indicating that the dominant factor driving the peak star formation history at z ≈ 2 is a larger supply of molecular gas in galaxies rather than a significant evolution of the SFR efficiency within individual galaxies.

7. MNRAS

   First Light And Reionization Epoch Simulations (FLARES) – II: The photometric properties of high-redshift galaxies

   Aswin P Vijayan, Christopher C Lovell, Stephen M Wilkins, and 5 more authors

   MNRAS, Mar 2021

   Abs DOI

   We present the photometric properties of galaxies in the First Light And Reionization Epoch Simulations (FLARES). The simulations trace the evolution of galaxies in a range of overdensities through the epoch of reionization. With a novel weighting scheme, we combine these overdensities, extending significantly the dynamic range of observed composite distribution functions compared to periodic simulation boxes. FLARES predicts a significantly larger number of intrinsically bright galaxies, which can be explained through a simple model linking dust attenuation to the metal content of the interstellar medium, using a line-of-sight extinction model. With this model, we present the photometric properties of the FLARES galaxies for z ∈ [5, 10]. We show that the ultraviolet (UV) luminosity function (LF) matches the observations at all redshifts. The function is fitted by Schechter and double power-law forms, with the latter being favoured at these redshifts by the FLARES composite UV LF. We also present predictions for the UV-continuum slope as well as the attenuation in the UV. The impact of environment on the UV LF is also explored, with the brightest galaxies forming in the densest environments. We then present the line luminosity and equivalent widths of some prominent nebular emission lines arising from the galaxies, finding rough agreement with available observations. We also look at the relative contribution of obscured and unobscured star formation, finding comparable contributions at these redshifts.

2020

1. MNRAS

   Nebular-line emission during the Epoch of Reionization

   Stephen M. Wilkins, Christopher C. Lovell, Ciaran Fairhurst, and 6 more authors

   MNRAS, Mar 2020

   Abs DOI

   Nebular emission lines associated with galactic H II regions carry information about both physical properties of the ionized gas and the source of ionizing photons as well as providing the opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. While nebular-line emission has been extensively studied at lower redshift there are currently only few constraints within the epoch of reionization (EoR; z \textgreater 6), chiefly due to the lack of sensitive near-IR spectrographs. However, this will soon change with the arrival of the Webb Telescope providing sensitive near-IR spectroscopy covering the rest-frame UV and optical emission of galaxies in the EoR. In anticipation of Webb, we combine the large cosmological hydrodynamical simulation BlueTides with photoionization modelling to predict the nebular emission-line properties of galaxies at z = 8 → 13. We find good agreement with the, albeit limited, existing direct and indirect observational constraints on equivalent widths though poorer agreement with luminosity function constraints.

2. NeurIPS

   Debunking Generalization Error or: How I Learned to Stop Worrying and Love My Training Set

   Viviana Acquaviva, Chistopher Lovell, and Emille Ishida

   NeurIPS, Nov 2020

   Abs

   We aim to determine some physical properties of distant galaxies (for example, stellar mass, star formation history, or chemical enrichment history) from their observed spectra, using supervised machine learning methods. We know that different astrophysical processes leave their imprint in various regions of the spectra with characteristic signatures. Unfortunately, identifying a training set for this problem is very hard, because labels are not readily available - we have no way of knowing the true history of how galaxies have formed. One possible approach to this problem is to train machine learning models on state-of-the-art cosmological simulations. However, when algorithms are trained on the simulations, it is unclear how well they will perform once applied to real data. In this paper, we attempt to model the generalization error as a function of an appropriate measure of distance between the source domain and the application domain. Our goal is to obtain a reliable estimate of how a model trained on simulations might behave on data.

2019

1. MNRAS

   Recalibrating the cosmic star formation history

   Stephen M. Wilkins, Christopher C. Lovell, and Elizabeth R. Stanway

   MNRAS, Dec 2019

   Abs DOI

   The calibrations linking observed luminosities to the star formation rate (SFR) depend on the assumed stellar population synthesis model, initial mass function, star formation and metal enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalization of the inferred cosmic star formation history is sensitive to these assumptions. Using v2.2.1 of the Binary Population and Spectral Synthesis (BPASS) model we determine a new set of calibration coefficients for the ultraviolet, thermal infrared, and hydrogen recombination lines. These ultraviolet and thermal infrared coefficients are 0.15-0.2 dex higher than those widely utilized in the literature while the H α coefficient is ∼0.35 dex larger. These differences arise in part due to the inclusion binary evolution pathways but predominantly reflect an extension in the IMF to 300 M⊙ and a change in the choice of reference metallicity. We use these new coefficients to recalibrate the cosmic star formation history, and find improved agreement between the integrated cosmic star formation history and the in situ measured stellar mass density as a function of redshift. However, these coefficients produce new tension between SFR densities inferred from the ultraviolet and thermal infrared and those from H α.

2. MNRAS

   Learning the relationship between galaxies spectra and their star formation histories using convolutional neural networks and cosmological simulations

   Christopher C. Lovell, Viviana Acquaviva, Peter A. Thomas, and 3 more authors

   MNRAS, Dec 2019

   Abs DOI

   We present a new method for inferring galaxy star formation histories (SFH) using machine learning methods coupled with two cosmological hydrodynamic simulations. We train convolutional neural networks to learn the relationship between synthetic galaxy spectra and high-resolution SFHs from the EAGLE and Illustris models. To evaluate our SFH reconstruction we use Symmetric Mean Absolute Percentage Error (SMAPE), which acts as a true percentage error in the low error regime. On dust-attenuated spectra we achieve high test accuracy (median SMAPE = 10.5 per cent). Including the effects of simulated observational noise increases the error (12.5 per cent), however this is alleviated by including multiple realizations of the noise, which increases the training set size and reduces overfitting (10.9 per cent). We also make estimates for the observational and modelling errors. To further evaluate the generalization properties we apply models trained on one simulation to spectra from the other, which leads to only a small increase in the error (median SMAPE ̃ 15 per cent). We apply each trained model to SDSS DR7 spectra, and find smoother histories than in the vespa catalogue. This new approach complements the results of existing spectral energy distribution fitting techniques, providing SFHs directly motivated by the results of the latest cosmological simulations.

2018

1. MNRAS

   Dust-obscured star-forming galaxies in the early universe

   Stephen M. Wilkins, Yu Feng, Tiziana Di Matteo, and 3 more authors

   MNRAS, Feb 2018

   Abs DOI

   Motivated by recent observational constraints on dust reprocessed emission in star-forming galaxies at z ∼ 6 and above, we use the very large cosmological hydrodynamical simulation BLUETIDES to explore predictions for the amount of dust-obscured star formation in the early Universe (z \textgreater 8). BLUETIDES matches current observational constraints on both the UV luminosity function and galaxy stellar mass function and predicts that approximately 90 per cent of the star formation in high-mass (M* \textgreater 1010 M⊙) galaxies at z = 8 is already obscured by dust. The relationship between dust attenuation and stellar mass predicted by BLUETIDES is consistent with that observed at lower redshift. However, observations of several individual objects at z \textgreater 6 are discrepant with the predictions, though it is possible that their uncertainties may have been underestimated. We find that the predicted surface density of z ≥ 8 submm sources is below that accessible to current Herschel, SCUBA-2 and Atacama Large Millimetre Array (ALMA) submm surveys. However, as ALMA continues to accrue an additional surface area the population of z \textgreater 8 dust-obscured galaxies may become accessible in the near future.

2. MNRAS

   Characterising and identifying galaxy protoclusters

   Christopher C. Lovell, Peter A. Thomas, and Stephen M. Wilkins

   MNRAS, Mar 2018

   Abs DOI

   We study the characteristics of galaxy protoclusters using the latest L-GALAXIES semi-analytic model. Searching for protoclusters on a scale of ˜10 cMpc gives an excellent compromise between the completeness and purity of their galaxy populations, leads to high distinction from the field in overdensity space, and allows accurate determination of the descendant cluster mass. This scale is valid over a range of redshifts and selection criteria. We present a procedure for estimating, given a measured galaxy overdensity, the protocluster probability and its descendant cluster mass for a range of modelling assumptions, particularly taking into account the shape of the measurement aperture. This procedure produces lower protocluster probabilities compared to previous estimates using fixed size apertures. The relationship between active galactic nucleus (AGN) and protoclusters is also investigated and shows significant evolution with redshift; at z ˜ 2, the fraction of protoclusters traced by AGN is high, but the fraction of all AGNs in protoclusters is low, whereas at z ≥ 5 the fraction of protoclusters containing AGN is low, but most AGNs are in protoclusters. We also find indirect evidence for the emergence of a passive sequence in protoclusters at z ˜ 2, and note that a significant fraction of all galaxies reside in protoclusters at z ≥ 2, particularly the most massive.

2017

1. MNRAS

   The properties of the first galaxies in the BlueTides simulation

   Stephen M. Wilkins, Yu Feng, Tiziana Di Matteo, and 3 more authors

   MNRAS, Aug 2017

   Abs DOI

   We employ the very large cosmological hydrodynamical simulation BlueTides to investigate the predicted properties of the galaxy population during the epoch of reionization (z \textgreater 8). BlueTides has a resolution and volume ((400/h ≈ 577)3 cMpc3) providing a population of galaxies that is well matched to depth and area of current observational surveys targeting the high-redshift Universe. At z = 8, BlueTides includes almost 160 000 galaxies with stellar masses \textgreater108 M⊙. The population of galaxies predicted by BlueTides closely matches observational constraints on both the galaxy stellar mass function and far-UV (150 nm) luminosity function. Galaxies in BlueTides are characterized by rapidly increasing star formation histories. Specific star formation rates decrease with redshift though remain largely insensitive to stellar mass. As a result of the enhanced surface density of metals, more massive galaxies are predicted to have higher dust attenuation resulting in a significant steepening of the observed far-UV luminosity function at high luminosities. The contribution of active supermassive black holes (SMBHs) to the UV luminosities of galaxies with stellar masses 109-10 M⊙ is around 3 per cent on average. Approximately 25 per cent of galaxies with M* ≈ 1010 M⊙ are predicted to have active SMBHs that contribute \textgreater10 per cent of the total UV luminosity.

2016

1. MNRAS

   The photometric properties of galaxies in the early Universe

   Stephen M. Wilkins, Yu Feng, Tiziana Di-Matteo, and 5 more authors

   MNRAS, Aug 2016

   Abs DOI

   We use the large cosmological hydro-dynamic simulation BLUETIDES to predict the photometric properties of galaxies during the epoch of reionization (z = 8-15). These properties include the rest-frame UV to near-IR broad-band spectral energy distributions, the Lyman continuum (LyC) photon production, the UV star formation rate calibration, and intrinsic UV continuum slope. In particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis (SPS) model, initial mass function, and the escape fraction of LyC photons, upon these quantities. We find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. For example, at z = 8 we predict that nebular emission can account for up to 50 per cent of the rest-frame R-band luminosity, while the choice of SPS model can change the LyC production rate up to a factor of ×2.