arXiv subjects

Mark Vogelsberger

Publications and source records attributed to Mark Vogelsberger.

At least 253 records · Page 14Linked to original sources

arXiv2021

The impact of galactic feedback on the shapes of dark-matter haloes

We quantify the impact of galaxy formation on dark matter halo shapes using cosmological simulations at redshift $z=0$. The haloes are drawn from the IllustrisTNG project, a suite of magneto-hydrodynamic simulations of galaxies. We focus on haloes of mass $10^{10-14} M_\odot$ from the 50-Mpc (TNG50) and 100-Mpc (TNG100) boxes, and compare them to dark matter-only (DMO) analogues and other simulations e.g. NIHAO and Eagle. We further quantify the prediction uncertainty by varying the baryonic feedback models in a series of smaller 25 Mpc $h^{-1}$ boxes. We find that: (i) galaxy formation results in rounder haloes compared to the DMO simulations, in qualitative agreement with past hydrodynamic models. Haloes of mass $\approx 2\times 10^{12} M_\odot$ are most spherical, with an average minor-to-major axis ratio of $\left< s \right> \approx 0.75$ in the inner halo, an increase of 40 per cent compared to their DMO counterparts. No significant change in halo shape is found for low-mass $10^{10} M_\odot$ haloes; (ii) stronger feedback, e.g. increasing galactic wind speed, reduces the impact of baryons; (iii) the inner halo shape correlates with the stellar mass fraction, which can explain the dependence of halo shapes on different feedback models; (iv) the fiducial and weaker feedback models are most consistent with observational estimates of the Milky Way halo shape. Yet, at fixed halo mass, very diverse and possibly unrealistic feedback models all predict inner halo shapes that are closer to one another than to the DMO results. This implies that a larger observational sample would be required to statistically distinguish between different baryonic prescriptions due to large halo-to-halo variation in halo shapes.

astro-ph.GA↗

arXiv2021

The Supersonic Project: SIGOs, a Proposed Progenitor to Globular Clusters, and their Connections to Gravitational Wave Anisotropies

Supersonically Induced Gas Objects (SIGOs), are structures with little to no dark matter component predicted to exist in regions of the Universe with large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. Using simulations, SIGOs have been studied on small scales (around 2 Mpc), where these relative velocities are coherent. However, it is challenging to study SIGOs using simulations on large scales due to the varying relative velocities at scales larger than a few Mpc. Here, we study SIGO abundances semi-analytically: using perturbation theory, we predict the number density of SIGOs analytically, and compare these results to small-box numerical simulations. We use the agreement between the numerical and analytic calculations to extrapolate the large-scale variation of SIGO abundances over different stream velocities. As a result, we predict similar large-scale variations of objects with high gas densities before reionization that could possibly be observed by JWST. If indeed SIGOs are progenitors of globular clusters, then we expect a similar variation of globular cluster abundances over large scales. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. As a proof-of-concept, and because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black hole (BBH) mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with SIGOs' distribution.

astro-ph.GA↗

arXiv2021

The Onset of Gravothermal Core Collapse in Velocity Dependent Self-Interacting Dark Matter Subhaloes

It has been proposed that gravothermal collapse due to dark matter self-interactions (i.e. self-interacting dark matter, SIDM) can explain the observed diversity of the Milky Way (MW) satellites' central dynamical masses. We investigate the process behind this hypothesis using an $N$-body simulation of a MW-analogue halo with velocity dependent self-interacting dark matter (vdSIDM) in which the low velocity self-scattering cross-section, $σ_{T}/m_{x}$, reaches 100 cm$^{2}$g$^{-1}$; we dub this model the vd100 model. We compare the results of this simulation to simulations of the same halo that employ different dark models, including cold dark matter (CDM) and other, less extreme SIDM models. The masses of the vd100 haloes are very similar to their CDM counterparts, but the values of their maximum circular velocities, $V_{max}$, are significantly higher. We determine that these high $V_{max}$ subhaloes were objects in the mass range [$5\times10^{6}$, $1\times10^{8}$] $M_\odot$ at $z=1$ that undergo gravothermal core collapse. These collapsed haloes have density profiles that are described by single power laws down to the resolution limit of the simulation, and the inner slope of this density profile is approximately $-3$. Resolving the ever decreasing collapsed region is challenging, and tailored simulations will be required to model the runaway instability accurately at scales $<1$ kpc.

astro-ph.GA↗

arXiv2021

Quenched fractions in the IllustrisTNG simulations: comparison with observations and other theoretical models

We make an in-depth comparison of the IllustrisTNG simulations with observational data on the quenched fractions of central and satellite galaxies, for $M_*=10^{9-12}M_{\odot}$ at $0\leq z\leq3$. We study how analysis methodologies and observational effects impact this comparison. This includes measurement choices -- aperture, quenched definition, star formation rate (SFR) indicator timescale -- as well as observational uncertainties and sample selection issues: projection effects, satellite/central misclassification, and host mass distribution sampling. The definition used to separate quenched and star-forming galaxies produces differences of up to 70 (30)$\%$ for centrals (satellites) $>\sim 10^{10.5} M_{\odot}$. Increasing the aperture within which SFR is measured can suppress the quenched fractions by up to $\sim50\%$, particularly at $z\gtrsim2$. Proper consideration of the stellar and host mass distributions is crucial: naive comparisons to volume-limited samples from simulations lead to misinterpretation of the quenched fractions as a function of $z$ by up to 20$\%$. Including observational uncertainties to theoretical values of $M_*$ and SFR changes the quenched fraction values and their trend and/or slope with mass. Taking projected rather than 3D distances for satellites decreases the quenched fractions by up to 10$\%$ due to field contamination. Comparing with data, TNG produces quenched fractions broadly consistent with observations. TNG predicts quenched fractions up to $\sim80-90\%$ for centrals at $z\leq2-3$, in line with recent observations, and notably higher than other theoretical models. The quantitative agreement of TNG and SDSS for satellite quenched fractions in groups and clusters depends strongly on the galaxy and host mass range. Our mock comparison between TNG and SDSS highlights the importance of properly accounting for observational effects and biases.

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arXiv2021

The halo mass function and inner structure of ETHOS haloes at high redshift

We study the halo mass function and inner halo structure at high redshifts ($z\geq5$) for a suite of simulations within the structure formation ETHOS framework. Scenarios such as cold dark matter (CDM), thermal warm dark matter (WDM), and dark acoustic oscillations (DAO) of various strengths are contained in ETHOS with just two parameters $h_{\rm peak}$ and $k_{\rm peak}$, the amplitude and scale of the first DAO peak. The Extended Press-Schechter (EPS) formalism with a smooth-$k$ filter is able to predict the cut-off in the halo mass function created by the suppression of small scale power in ETHOS models (controlled by $k_{\rm peak}$), as well as the slope at small masses that is dependent on $h_{\rm peak}$. Interestingly, we find that DAOs introduce a localized feature in the mass distribution of haloes, resulting in a mass function that is distinct in shape compared to either CDM or WDM. We find that the halo density profiles of ${\it all}$ ETHOS models are well described by the NFW profile, with a concentration that is lower than in the CDM case in a way that is regulated by $k_{\rm peak}$. We show that the concentration-mass relation for DAO models can be well approximated by the mass assembly model based on the extended Press-Schechter theory, which has been proposed for CDM and WDM elsewhere. Our results can be used to perform inexpensive calculations of the halo mass function and concentration-mass relation within the ETHOS parametrization without the need of $N-$body simulations.

astro-ph.CO↗

arXiv2021

Inferring the Morphology of Stellar Distribution in TNG50: Twisted and Twisted-Stretched shapes

We investigate the morphology of the stellar distribution in a sample of Milky Way (MW) like galaxies in the TNG50 simulation. Using a local in shell iterative method (LSIM) as the main approach, we explicitly show evidence of twisting (in about 52% of halos) and stretching (in 48% of them) in the real space. This is matched with the re-orientation observed in the eigenvectors of the inertia tensor and gives us a clear picture of having a re-oriented stellar distribution. We make a comparison between the shape profile of dark matter (DM) halo and stellar distribution and quite remarkably see that their radial profiles are fairly close, especially at small galactocentric radii where the stellar disk is located. This implies that the DM halo is somewhat aligned with stars in response to the baryonic potential. The level of alignment mostly decreases away from the center. We study the impact of substructures in the orbital circularity parameter. It is demonstrated that in some cases, far away substructures are counter-rotating compared with the central stars and may flip the sign of total angular momentum and thus the orbital circularity parameter. Truncating them above 150 kpc, however, retains the disky structure of the galaxy as per initial selection. Including the impact of substructures in the shape of stars, we explicitly show that their contribution is subdominant. Overlaying our theoretical results to the observational constraints from previous literature, we establish fair agreement.

astro-ph.GA↗

arXiv2021

The splashback boundary of haloes in hydrodynamic simulations

The splashback radius, $R_{\rm sp}$, is a physically motivated halo boundary that separates infalling and collapsed matter of haloes. We study $R_{\rm sp}$ in the hydrodynamic and dark matter only IllustrisTNG simulations. The most commonly adopted signature of $R_{\rm sp}$ is the radius at which the radial density profiles are steepest. Therefore, we explicitly optimise our density profile fit to the profile slope and find that this leads to a $\sim5\%$ larger radius compared to other optimisations. We calculate $R_{\rm sp}$ for haloes with masses between $10^{13-15}{\rm M}_{\odot}$ as a function of halo mass, accretion rate and redshift. $R_{\rm sp}$ decreases with mass and with redshift for haloes of similar $M_{\rm200m}$ in agreement with previous work. We also find that $R_{\rm sp}/R_{\rm200m}$ decreases with halo accretion rate. We apply our analysis to dark matter, gas and satellite galaxies associated with haloes to investigate the observational potential of $R_{\rm sp}$. The radius of steepest slope in gas profiles is consistently smaller than the value calculated from dark matter profiles. The steepest slope in galaxy profiles, which are often used in observations, tends to agree with dark matter profiles but is lower for less massive haloes. We compare $R_{\rm sp}$ in hydrodynamic and N-body dark matter only simulations and do not find a significant difference caused by the addition of baryonic physics. Thus, results from dark matter only simulations should be applicable to realistic haloes.

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arXiv2021

Properties of the ionized CGM and IGM: a comparison of galaxy formation models via the Sunyaev-Zel'dovich effect

We present a comparison of the physical properties of the ionized gas in the circumgalactic (CGM) and intergalactic (IGM) media at $z\sim0$ between observations and four cosmological hydrodynamical simulations: Illustris, TNG300 of the IllustrisTNG project, EAGLE, and one of the Magneticum simulations. For the observational data, we use the gas properties that are inferred from cross-correlating the Sunyaev-Zel'dovich effect (SZE) from the {\it Planck} CMB maps with the haloes and the large-scale structure reconstructed from Sloan Digital Sky Survey data. Both the observational and simulation results indicate that the integrated gas pressure in haloes deviates from the self-similar case, showing that feedback impacts haloes with $M_{500}\sim 10^{12-13}\,{\rm M_\odot}$. The simulations predict that more than half the baryons are displaced from haloes, while the gas fraction inferred from our observational data roughly equals the cosmic baryon fraction throughout the $M_{500}\sim 10^{12-14.5}\,{\rm M_\odot}$ halo mass range. All simulations tested here predict that the mean gas temperature in haloes is about the virial temperature, while that inferred from the SZE is up to one order of magnitude lower than that from the simulations (and also from X-ray observations). While a remarkable agreement is found for the average properties of the IGM between the observation and some simulations, we show that their dependence on the large-scale tidal field can break the degeneracy between models that show similar predictions otherwise. Finally, we show that the gas pressure and the electron density profiles from simulations are not well described by a generalized NFW (GNFW) profile. Instead, we present a new model with a mass-dependent shape that fits the profiles accurately.

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arXiv2021

DM halo morphological types of MW-like galaxies in the TNG50 simulation: Simple, Twisted, or Stretched

We present a comprehensive analysis of the shape of dark matter (DM) halos in a sample of 25 Milky Way-like galaxies in TNG50 simulation. Using an Enclosed Volume Iterative Method (EVIM), we infer an oblate-to-triaxial shape for the DM halo with the median $T \simeq 0.24 $. We group DM halos in 3 different categories. Simple halos (32% of population) establish principal axes whose ordering in magnitude does not change with radius and whose orientations are almost fixed throughout the halo. Twisted halos (32% of population), experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36% of population) demonstrate a stretching in their principal axes lengths where the ordering of different eigenvalues change with radius. Subsequently, the halo experiences a "rotation" of $\sim$90 deg where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of re-orienting ellipsoid in twisted and stretched halos. We examine the impact of baryonic physics on DM halo shape through a comparison to dark matter only (DMO) simulations. This suggests a triaxial (prolate) halo. We analyze the impact of substructure on DM halo shape in both hydro and DMO simulations and confirm that their impacts are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle of satellites' angular momentum with galaxy's angular momentum grows with radius. However, stretched halos show a flat distribution of angles. Overlaying our theoretical outcome on the observational results presented in the literature establishes a fair agreement.

astro-ph.GA↗

arXiv2021

Hot and counter-rotating star-forming disk galaxies in IllustrisTNG and their real-world counterparts

A key feature of a large population of low-mass, late-type disk galaxies are star-forming disks with exponential light distributions. They are typically also associated with thin and flat morphologies, blue colors, and dynamically cold stars moving along circular orbits within co-planar thin gas disks. However, the latter features do not necessarily always imply the former, in fact, a variety of different kinematic configurations do exist. In this work, we use the cosmological hydrodynamical IllustrisTNG Simulation to study the nature and origin of dynamically hot, sometimes even counter-rotating, star-forming disk galaxies in the lower stellar mass range (between $5\times 10^9\,\mathrm{M_{\odot}}$ and $2\times 10^{10}\,\mathrm{M_{\odot}}$). We find that being dynamically hot arises in most cases as an induced transient state, for example due to galaxy interactions and merger activities, rather than as an age-dependent evolutionary phase of star-forming disk galaxies. The dynamically hot but still actively star-forming disks show a common feature of hosting kinematically misaligned gas and stellar disks, and centrally concentrated on-going star formation. The former is often accompanied by disturbed gas morphologies, while the latter is reflected in low gas and stellar spins in comparison to their dynamically cold, normal disk counterparts. Interestingly, observed galaxies from MaNGA with kinematic misalignment between gas and stars show remarkably similar general properties as the IllustrisTNG galaxies, and therefore are plausible real-world counterparts. In turn, this allows us to make predictions for the stellar orbits and gas properties of these misaligned galaxies.

astro-ph.GA↗

arXiv2021

Submillimetre galaxies in cosmological hydrodynamical simulations -- an opportunity for constraining feedback models

Submillimetre galaxies (SMGs) have long posed a challenge for theorists, and self-consistently reproducing the properties of the SMG population in a large-volume cosmological hydrodynamical simulation has not yet been achieved. We use a scaling relation derived from previous simulations plus radiative transfer calculations to predict the submm flux densities of simulated SMGs drawn from cosmological simulations from the Illustris and IllustrisTNG projects based on the simulated galaxies' star formation rates (SFRs) and dust masses and compare the predicted number counts with observations. We find that the predicted SMG number counts based on IllustrisTNG are significantly less than observed (more than 1 dex at $S_{850} \gtrsim 4$ mJy). The simulation from the original Illustris project yields more SMGs than IllustrisTNG: the predicted counts are consistent with those observed at both $S_{850} \lesssim 5$ mJy and $S_{850} \gtrsim 9$ mJy and only a factor of $\sim 2$ lower than observed at intermediate flux densities. The redshift distribution of SMGs with $S_{850} > 3$ mJy in IllustrisTNG is consistent with the observed distribution, whereas the Illustris redshift distribution peaks at significantly lower redshift (1.5 vs. 2.8). We demonstrate that IllustrisTNG hosts fewer SMGs than Illustris because in the former, high-mass ($M_{\star} \sim 10^{11} \, \text{M}_{\odot}$) $z \sim 2-3$ galaxies have lower dust masses and SFRs than in Illustris owing to differences in the sub-grid models for stellar or/and active galactic nucleus (AGN) feedback between the two simulations (we unfortunately cannot isolate the specific cause(s) post hoc). Our results demonstrate that because our method enables predicting SMG number counts in post-processing with a negligible computational expense, SMGs can provide useful constraints for tuning sub-grid models in future large-volume cosmological simulations.

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arXiv2021

The IllustrisTNG Simulations: Public Data Release

We present the full public release of all data from the TNG50, TNG100 and TNG300 simulations of the IllustrisTNG project. IllustrisTNG is a suite of large volume, cosmological, gravo-magnetohydrodynamical simulations run with the moving-mesh code Arepo. TNG includes a comprehensive model for galaxy formation physics, and each TNG simulation self-consistently solves for the coupled evolution of dark matter, cosmic gas, luminous stars, and supermassive blackholes from early time to the present day, z=0. Each of the flagship runs -- TNG50, TNG100, and TNG300 -- are accompanied by lower-resolution and dark-matter only counterparts, and we discuss scientific and numerical cautions and caveats relevant when using TNG. Full volume snapshots are available at 100 redshifts; halo and subhalo catalogs at each snapshot and merger trees are also released. The data volume now directly accessible online is ~1.1 PB, including 2,000 full volume snapshots and ~110,000 high time-resolution subbox snapshots. Data access and analysis examples are available in IDL, Python, and Matlab. We describe improvements and new functionality in the web-based API, including on-demand visualization and analysis of galaxies and halos, exploratory plotting of scaling relations and other relationships between galactic and halo properties, and a new JupyterLab interface. This provides an online, browser-based, near-native data analysis platform which supports user computation with fully local access to TNG data, alleviating the need to download large simulated datasets.

astro-ph.GA↗

arXiv2021

Spatially Resolved Star Formation and Inside-out Quenching in the TNG50 Simulation and 3D-HST Observations

We compare the star forming main sequence (SFMS) -- both integrated and resolved on 1kpc scales -- between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z~1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2-1dex between observed and simulated main sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M_*>10^10Msun, even after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M_*>10^10.5Msun, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In TNG this inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates. In contrast, the original Illustris simulation, without this same physical SMBH mechanism, does not reproduce the central SFR profile suppression seen in data. The observed sSFR profiles provide support for the TNG quenching mechanism and how it affects gas on kiloparsec scales in the centers of galaxies.

astro-ph.GA↗

arXiv2021

The cumulative star-formation histories of dwarf galaxies with TNG50. I: Environment-driven diversity and connection to quenching

We present the cumulative star-formation histories (SFHs) of >15000 dwarf galaxies ($M_{*}=10^{7-10}M_{\odot}$) from the TNG50 run of the IllustrisTNG suite across a vast range of environments. The key factors determining the dwarfs' SFHs are their status as central or satellite and their stellar mass, with centrals and more massive dwarfs assembling their stellar mass at later times on average compared to satellites and lower mass dwarfs. The satellites (in hosts of total mass $M_{200c,\,host}=10^{12-14.3}M_{\odot}$) assembled 90% of their z=0 stellar mass ~$7.0_{-5.5}^{+3.3}$ Gyr ago, while the centrals did so only ~$1.0_{-0.5}^{+4.0}$ Gyr ago. TNG50 predicts a large diversity in SFHs for both centrals and satellites, so that the stacked cumulative SFHs are representative of the TNG50 dwarf populations only in an average sense and individual dwarfs can have significantly different cumulative SFHs. Satellite dwarfs with the highest stellar mass to host mass ratios have the latest stellar mass assembly. Satellites at fixed stellar and host halo mass, found closer to the cluster centre, or accreted at earlier times, show significantly earlier stellar mass assembly. These trends, as well as the shapes of the SFHs themselves, are a manifestation of the varying proportions within a given subsample of quenched vs. star-forming galaxies, which exhibit markedly distinct SFH shapes. We also find a subtle effect whereby satellite dwarfs in the most massive hosts at z=0 have higher SFRs at early times, well before final infall into their z=0 host, compared to a control sample of centrals mass-matched at the time of accretion. This suggests that the large-scale environment can have a mild effect even on future satellites by providing the conditions for enhanced SF at early epochs. Our results are useful theoretical predictions for comparison to future resolved-stellar-population observations.

astro-ph.GA↗

arXiv2021

The dust-continuum size of TNG50 galaxies at $z=1-5$: a comparison with the distribution of stellar light, stars, dust and H$_2$

We present predictions for the extent of the dust-continuum emission of thousands of main-sequence galaxies drawn from the TNG50 simulation between $z=1-5$. To this aim, we couple the radiative transfer code SKIRT to the output of the TNG50 simulation and measure the dust-continuum half-light radius of the modeled galaxies, assuming a Milky Way dust type and a metallicity dependent dust-to-metal ratio. The dust-continuum half-light radius at observed-frame 850 $μ$m is up to $\sim$75 per cent larger than the stellar half-mass radius, but significantly more compact than the observed-frame 1.6 $μ$m (roughly corresponding to H-band) half-light radius, particularly towards high redshifts: the compactness compared to the 1.6 $μ$m emission increases with redshift. This is driven by obscuration of stellar light from the galaxy centres, which increases the apparent extent of 1.6 $μ$m disk sizes relative to that at 850 $μ$m. The difference in relative extents increases with redshift because the observed-frame 1.6 $μ$m emission stems from ever shorter wavelength stellar emission. These results suggest that the compact dust-continuum emission observed in $z>1$ galaxies is not (necessarily) evidence of the buildup of a dense central stellar component. We also find that the dust-continuum half-light radius very closely follows the radius containing half the star formation in galaxies, indicating that single band dust-continuum emission is a good tracer of the location of (obscured) star formation. The dust-continuum emission is more compact than the H2 mass (for galaxies at $z\geq 2$) and the underlying dust mass. The dust emission strongly correlates with locations with the highest dust temperatures, which do not need to be the locations where most H$_2$ and/or dust is located. The presented results are a common feature of main-sequence galaxies.

astro-ph.GA↗

arXiv2020

Molecular hydrogen in IllustrisTNG galaxies: carefully comparing signatures of environment with local CO & SFR data

We examine how the post-processed content of molecular hydrogen (H$_2$) in galaxies from the TNG100 cosmological, hydrodynamic simulation changes with environment at $z\!=\!0$, assessing central/satellite status and host halo mass. We make close comparisons with the carbon monoxide (CO) emission survey xCOLD GASS where possible, having mock-observed TNG100 galaxies to match the survey's specifications. For a representative sample of host haloes across $10^{11}\!\lesssim\!M_{\rm 200c}/{\rm M}_{\odot}\!<\!10^{14.6}$, TNG100 predicts that satellites with $m_*\!\geq\!10^9\,{\rm M}_{\odot}$ should have a median deficit in their H$_2$ fractions of $\sim$0.6 dex relative to centrals of the same stellar mass. Once observational and group-finding uncertainties are accounted for, the signature of this deficit decreases to $\sim$0.2 dex. Remarkably, we calculate a deficit in xCOLD GASS satellites' H$_2$ content relative to centrals of 0.2--0.3 dex, in line with our prediction. We further show that TNG100 and SDSS data exhibit continuous declines in the average star formation rates of galaxies at fixed stellar mass in denser environments, in quantitative agreement with each other. By tracking satellites from their moment of infall in TNG100, we directly show that atomic hydrogen (HI) is depleted at fractionally higher rates than H$_2$ on average. Supporting this picture, we find that the H$_2$/HI mass ratios of satellites are elevated relative to centrals in xCOLD GASS. We provide additional predictions for the effect of environment on H$_2$ -- both absolute and relative to HI -- that can be tested with spectral stacking in future CO surveys.

astro-ph.GA↗

arXiv2020

The relationship between fine galaxy stellar morphology and star formation activity in cosmological simulations: a deep learning view

Hydrodynamical simulations of galaxy formation and evolution attempt to fully model the physics that shapes galaxies. The agreement between the morphology of simulated and real galaxies, and the way the morphological types are distributed across galaxy scaling relations are important probes of our knowledge of galaxy formation physics. Here we propose an unsupervised deep learning approach to perform a stringent test of the fine morphological structure of galaxies coming from the Illustris and IllustrisTNG (TNG100 and TNG50) simulations against observations from a subsample of the Sloan Digital Sky Survey. Our framework is based on PixelCNN, an autoregressive model for image generation with an explicit likelihood. We adopt a strategy that combines the output of two PixelCNN networks in a metric that isolates the fine morphological details of galaxies from the sky background. We are able to \emph{quantitatively} identify the improvements of IllustrisTNG, particularly in the high-resolution TNG50 run, over the original Illustris. However, we find that the fine details of galaxy structure are still different between observed and simulated galaxies. This difference is driven by small, more spheroidal, and quenched galaxies which are globally less accurate regardless of resolution and which have experienced little improvement between the three simulations explored. We speculate that this disagreement, that is less severe for quenched disky galaxies, may stem from a still too coarse numerical resolution, which struggles to properly capture the inner, dense regions of quenched spheroidal galaxies.

astro-ph.GA↗

arXiv2020

The Origin of the Dust Extinction Curve in Milky Way-like Galaxies

We develop a cosmological model for the evolution of dust grains in galaxies with a distribution of sizes in order to understand the origin of the Milky Way dust extinction curve. Our model considers the formation of active dust in evolved stars, growth by accretion and coagulation, and destruction processes via shattering, sputtering, and astration in the ISM of galaxies over cosmic time. Our main results follow. Galaxies in our cosmological model with masses comparable to the Milky Way's at z~0 exhibit a diverse range of extinction laws, though with slopes and bump strengths comparable to the range observed in the Galaxy. The progenitors of the Milky Way have steeper slopes, and only flatten to slopes comparable to the Galaxy at $z \approx 1$. This owes to increased grain growth rates at late times/in high-metallicity environments driving up the ratio of large to small grains, with a secondary dependence on the graphite to silicate ratio evolution. The UV bump strengths depend primarily on the graphite to silicate ratio, and remain broadly constant in MW-like galaxies between z=3 and z=0, though show slight variability. Our models span comparable regions of bump-slope space as sightlines in the Galaxy do, though there is a lack of clear relationship between the model slopes and bump strengths owing to small scale fluctuations in the bump strength. Our models naturally produce slopes for some non-Milky Way analogs as steep as those of the LMC and SMC in metal poor galaxies, though notably the bump strengths are, on average, too large when comparing to the Magellanic clouds. This owes to the fact that we evolve the grain size distributions of graphites and silicates simultaneously, which is an oversimplification. Our model provides a novel framework to study the origins and variations of dust extinction curves in galaxies over cosmic time.

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