Cosmological hydrodynamic simulations have, in recent years, become capable of matching key distribution functions in the local universe, such as those of stellar mass and star formation rate. However, high resolution, large volume simulations have rarely been tested in the high redshift (z > 5) regime, particularly in the most overdense environments. Creating models that fit both high redshift and low redshift observables self consistently is a significant challenge, but key to understanding the properties of galaxies in the first billion years of the universe’s history, and how this affects their latter evolution. Such models are also necessary to make detailed predictions, and plan observations, for upcoming space based instruments, such as JWST, WFIRST and Euclid.
Figure of merit showing the general anti-correlation between simulation resolution and volume probed. FLARES is able to break this correlation, and explore much larger effective volumes at high fidelity.
The First Light And Reionisation Epoch Simulations (FLARES) are one approach to these issues. FLARES consists of a suite of 40 ‘zoom’ simulations using a modified version of the EAGLE code. We selected regions at high redshift, with a range of overdensities, from an enormous periodic dark matter-only volume, and resimulated these with full hydrodynamics at fiducial EAGLE resolution.
I led the first release paper (Lovell et al., 2021) in which we study predictions for the galaxy stellar mass function, star formation rate function and star-forming sequence as a function of environment. I also led a paper studying passive galaxy populations in the high redshift (z > 5) regime (Lovell et al., 2023). Further work with the FLARES suite is described in (Vijayan et al., 2021; Vijayan et al., 2022; Roper et al., 2022; Wilkins et al., 2022; D’Silva et al., 2023; Roper et al., 2023; Wilkins et al., 2023; Wilkins et al., 2023; Seeyave et al., 2023; Thomas et al., 2023; Vijayan et al., 2024; Wilkins et al., 2023; Wilkins et al., 2024; Punyasheel et al., 2024; Wilkins et al., 2024; Maltz et al., 2024)
References
2024
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
2023
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
2022
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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
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.
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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
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.
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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
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.
2021
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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
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.
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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
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.