Simba is “a state-of-the-art suite of galaxy formation simulations for exploring the co-evolution of galaxies, black holes, and intergalactic gas within a cosmological context”.
The Simba simulations are part of the CAMELS suite, and have been used to explore a range of questions in the field of galaxy formation and evolution.
I was involved in a project modelling the sub-mm population in Simba using the Powderday code (Narayanan et al., 2021), achieving one of the best matches to observational constraints on the 850-micron number counts in a hydrodynamical simulation to date (Lovell et al., 2021). We also explored the orientation dependence of the FIR-mm emission, finding interesting dependencies on the relative inclination (Lovell et al., 2022).
Forward modelled Simba galaxies on the star formation rate (SFR) - dust mass plane, coloured by their 850 micron emission. The redshift evolution is shown by the coloured lines, in bins of SFR.
I have also been involved with a number of other Simba projects, modelling dust and cold gas at high-z (Lorenzon et al., 2024), number counts of radio sources (Hale et al., 2022), emission line diagnostics (Garg et al., 2022), circumgalactic medium observations (Appleby et al., 2023), and understanding the efficiency of star formation (Ghodsi et al., 2024).
References
2024
-
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
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).
-
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
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.
2023
-
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
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.
2022
-
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
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.
-
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
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.
-
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
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.
2021
-
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
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.
-
Reproducing submillimetre galaxy number counts with cosmological hydrodynamic simulations
Christopher C. Lovell, James E. Geach, Romeel Davé, and 2 more authors
MNRAS, Mar 2021
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.
