arXiv subjects

Annalisa Pillepich

Publications and source records attributed to Annalisa Pillepich.

At least 109 records · Page 6Linked to original sources

arXiv2022

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

We report the discovery of ancient massive merger events in the early-type galaxies NGC 1380 and NGC 1427, members of the Fornax galaxy cluster. Both galaxies have been observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recently-developed population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metallicity maps, we obtain the stellar orbits, age and metallicity distributions of each galaxy. We then decompose each galaxy into multiple orbital-based components, including a dynamically hot inner stellar halo component which is identified as the relic of past massive mergers. By comparing to analogues from cosmological galaxy simulations, chiefly TNG50, we find that the formation of such a hot inner stellar halo requires the merger with a now-destroyed massive satellite galaxy of $3.7_{-1.5}^{+2.7} \times 10^{10}$ Msun (about $1/5$ of its current stellar mass) in the case of NGC 1380 and of $1.5_{-0.7}^{+1.6} \times10^{10}$ Msun (about $1/4$ of its current stellar mass) in the case of NGC 1427. Moreover, we infer that the last massive merger in NGC 1380 happened $\sim10$ Gyr ago based on the stellar age distribution of the re-grown dynamically cold disk, whereas the merger in NGC 1427 ended $t\lesssim 8$ Gyr ago based on the stellar populations in its hot inner stellar halo. The major merger event in NGC 1380 is the first one with both merger mass and merger time quantitatively inferred in a galaxy beyond the Local Volume. Moreover, it is the oldest and most massive merger uncovered in nearby galaxies so far.

astro-ph.GA↗

arXiv2022

Gas Accretion Can Drive Turbulence in Galaxies

The driving of turbulence in galaxies is deeply connected with the physics of feedback, star formation, outflows, accretion, and radial transport in disks. The velocity dispersion of gas in galaxies therefore offers a promising observational window into these processes. However, the relative importance of each of these mechanisms remains controversial. In this work we revisit the possibility that turbulence on galactic scales is driven by the direct impact of accreting gaseous material on the disk. We measure this effect in a disk-like star-forming galaxy in IllustrisTNG, using the high-resolution cosmological magnetohydrodynamical simulation TNG50. We employ Lagrangian tracer particles with a high time cadence of only a few Myr to identify accretion and other events, such as star formation, outflows, and movement within the disk. The energies of particles as they arrive in the disk are measured by stacking the events in bins of time before and after the event. The average effect of each event is measured on the galaxy by fitting explicit models for the kinetic and turbulent energies as a function of time in the disk. These measurements are corroborated by measuring the cross-correlation of the turbulent energy in the different annuli of the disk with other time series, and searching for signals of causality, i.e. asymmetries in the cross-correlation across zero time lag. We find that accretion contributes to the large-scale turbulent kinetic energy even if it is not the dominant driver of turbulence in this $\sim 5 \times 10^{9} M_\odot$ stellar mass galaxy. Extrapolating this finding to a range of galaxy masses, we find that there are regimes where energy from direct accretion may dominate the turbulent energy budget, particularly in disk outskirts, galaxies less massive than the Milky Way, and at redshift $\sim 2$.

astro-ph.GA↗

arXiv2022

The buildup of strongly barred galaxies in the TNG100 simulation

We analyse the properties of strongly barred disc galaxies using the TNG100 simulation, a cosmological hydrodynamical realisation of the IllustrisTNG suite. We identify 270 disc galaxies at $z=0$ in the stellar mass range $M_{*}=10^{10.4-11}M_{\odot}$, of which 40 per cent are barred. Of the detected bars, more than half are strong. We find that the fraction of barred galaxies increases with stellar mass, in agreement with observational results. Strongly barred galaxies exhibit, overall, lower gas-to-stellar mass ratios compared to unbarred galaxies. The majority of barred galaxies are quenched (sSFR $\sim10^{-11.7} $yr$^{-1}$), whereas unbarred galaxies continue to be active (sSFR $\sim10^{-10.3}$yr$^{-1}$) on the main sequence of star-forming galaxies. We explore the evolution of strongly barred and unbarred galaxies to investigate their formation and quenching histories. We find that strong bars form between $0.5< z< 1.5$, with more massive galaxies hosting older bars. Strong bars form in galaxies with an early-established prominent disc component, undergoing periods of enhanced star formation and black hole accretion, possibly assisted by cosmological inflows. Unbarred galaxies, on the other hand, assemble most of their mass and disc component at late times. The nuclear region of strongly barred galaxies quenches shortly after bar formation, while unbarred galaxies remain active across time. Our findings are indicative of bar quenching, possibly assisted by nuclear feedback processes. We conclude that the cosmological environment, together with small scale feedback processes, determine the chances of a galaxy to form a bar and to rapidly quench its central region.

astro-ph.GA↗

arXiv2022

ERGO-ML I: Inferring the assembly histories of IllustrisTNG galaxies from integral observable properties via invertible neural networks

A fundamental prediction of the LambdaCDM cosmology is the hierarchical build-up of structure and therefore the successive merging of galaxies into more massive ones. As one can only observe galaxies at one specific time in cosmic history, this merger history remains in principle unobservable. By using the TNG100 simulation of the IllustrisTNG project, we show that it is possible to infer the unobservable stellar assembly and merger history of central galaxies from their observable properties by using machine learning techniques. In particular, in this first paper of ERGO-ML (Extracting Reality from Galaxy Observables with Machine Learning), we choose a set of 7 observable integral properties of galaxies (i.e. total stellar mass, redshift, color, stellar size, morphology, metallicity, and age) to infer, from those, the stellar ex-situ fraction, the average merger lookback times and mass ratios, and the lookback time and stellar mass of the last major merger. To do so, we use and compare a Multilayer Perceptron Neural Network and a conditional Invertible Neural Network (cINN): thanks to the latter we are also able to infer the posterior distribution for these parameters and hence estimate the uncertainties in the predictions. We find that the stellar ex-situ fraction and the time of the last major merger are well determined by the selected set of observables, that the mass-weighted merger mass ratio is unconstrained, and that, beyond stellar mass, stellar morphology and stellar age are the most informative properties. Finally, we show that the cINN recovers the remaining unexplained scatter and secondary cross-correlations. Our tools can be applied to large galaxy surveys in order to infer unobservable properties of galaxies' past, enabling empirical studies of galaxy evolution enriched by cosmological simulations.

astro-ph.GA↗

arXiv2022

The distinct stellar-to-halo mass relations of satellite and central galaxies: insights from the IllustrisTNG simulations

We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above 10^10.5 Msun using the suite of cosmological magneto-hydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and cluster-like hosts with total masses of 10^12-15.2 Msun. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabit higher local density environments; moreover, it is in place already at early times (z < 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals, over the whole range of dynamical mass (by up to 0.8 dex). The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: the departure of the satellite SHMR from the centrals' relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG.

astro-ph.GA↗

arXiv2022

Cold Gas in Massive Galaxies as A Critical Test of Black Hole Feedback Models

Black hole feedback has been widely implemented as the key recipe to quench star formation in massive galaxies in modern semi-analytic models and hydrodynamical simulations. As the theoretical details surrounding the accretion and feedback of black holes continue to be refined, various feedback models have been implemented across simulations, with notable differences in their outcomes. Yet, most of these simulations have successfully reproduced some observations, such as stellar mass function and star formation rate density in the local Universe. We use the recent observation on the change of neutral hydrogen gas mass (including both ${\rm H_2}$ and ${\rm HI}$) with star formation rate of massive central disc galaxies as a critical constraint of black hole feedback models across several simulations. We find that the predictions of IllustrisTNG agree with the observations much better than the other models tested in this work. This favors IllustrisTNG's treatment of active galactic nuclei - where kinetic winds are driven by black holes at low accretion rates - as more plausible amongst those we test. In turn, this also indirectly supports the idea that the massive central disc galaxy population in the local Universe was likely quenched by AGN feedback.

astro-ph.GA↗

arXiv2022

Co-evolution of massive black holes and their host galaxies at high redshift: discrepancies from six cosmological simulations and the key role of JWST

The James Webb Space Telescope will have the power to characterize high-redshift quasars at z>6 with an unprecedented depth and spatial resolution. While the brightest quasars at such redshift (i.e., with bolometric luminosity L_bol> 10^46 erg/s) provide us with key information on the most extreme objects in the Universe, measuring the black hole (BH) mass and Eddington ratios of fainter quasars with L_bol= 10^45-10^46 erg/s opens a path to understand the build-up of more normal BHs at z>6. In this paper, we show that the Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA large-scale cosmological simulations do not agree on whether BHs at z>4 are overmassive or undermassive at fixed galaxy stellar mass with respect to the M_BH-M_star scaling relation at z=0 (BH mass offsets). Our conclusions are unchanged when using the local scaling relation produced by each simulation or empirical relations. We find that the BH mass offsets of the simulated faint quasar population at z>4, unlike those of bright quasars, represent the BH mass offsets of the entire BH population, for all the simulations. Thus, a population of faint quasars with L_bol= 10^45-10^46 erg/s observed by JWST can provide key constraints on the assembly of BHs at high redshift. Moreover, this will help constraining the high-redshift regime of cosmological simulations, including BH seeding, early growth, and co-evolution with the host galaxies. Our results also motivate the need for simulations of larger cosmological volumes down to z=6, with the same diversity of sub-grid physics, in order to gain statistics on the most extreme objects at high redshift.

astro-ph.CO↗

arXiv2022

Simulated Bars May Be Shorter But Are Not Slower Than Observed: TNG50 vs. MaNGA

Galactic bars are prominent dynamical structures within disk galaxies whose size, formation time, strength, and pattern speed influence the dynamical evolution of their hosts galaxies. Yet, their formation and evolution in a cosmological context is not well understood, as cosmological simulation studies have been limited by the classic trade off between simulation volume and resolution. Here we analyze barred disk galaxies in the cosmological magneto-hydrodynamical simulation TNG50 and quantitatively compare the distributions of bar size and pattern speed to those from MaNGA observations at $z=0$. TNG50 galaxies are selected to match the stellar mass and size distributions of observed galaxies, to account for observational selection effects. We find that the high-resolution of TNG50 yields bars with a wide range of pattern speeds (including those with $\geq 40~\mathrm{km}\,\mathrm{s}^{-1}$\,$\mathrm{kpc}^{-1}$) and a mean value of $\sim36~\mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{kpc}$ consistent with observations within $6\,\mathrm{km}\,\mathrm{s}^{-1}$\,$\mathrm{kpc}^{-1}$, in contrast with previous lower-resolution cosmological simulations that produced bars that were too slow. We find, however, that bars in TNG50 are on average $\sim 35\%$ shorter than observed, although this discrepancy may partly reflect remaining inconsistencies in the simulation-data comparison. This leads to higher values of $\mathcal{R} = R_\mathrm{corot}/R_\mathrm{bar}$ in TNG50, but points to simulated bars being `too short' rather than `too slow'. After repeating the analysis on the lower-resolution run of the same simulation (with the same physical model), we qualitatively reproduce the results obtained in previous studies: this implies that, along with physical model variations, numerical resolution effects may explain the previously found `slowness' of simulated bars.

astro-ph.GA↗

arXiv2022

Mass of the dynamically hot inner stellar halo predicts the ancient accreted stellar mass

Galactic dynamical structures are fossil records of the assembly histories of galaxies. By analyzing the cosmological hydrodynamical simulation TNG50, we find that a dynamical structure that we call the "hot inner stellar halo," defined by stars on dynamically hot orbits with circularity $λ_z < 0.5$ at $3.5\,{\rm kpc}<r \lesssim 2\,R_e$, is a strong indicator of the mass of accreted satellite galaxies. We find a strong correlation between the mass of this hot inner stellar halo and the total ex situ stellar mass. There is a similarly strong correlation with the stellar mass of the most massive secondary galaxy ever merged. These TNG50 correlations are compatible with those predicted by other simulations, for example by TNG100 across the whole mass range under study (galaxy stellar masses, $M_*$, in the $10^{10.3-11.6}$\,\Msun\, range) and by EAGLE for $M_* \gtrsim 10^{10.6} $\,\Msun\, galaxies.\ This shows that our predictions are robust across different galaxy formation and feedback models and hold across a wide range of numerical resolution. The hot inner stellar halo is a product of massive and typically ancient mergers, with inner-halo stars exhibiting three main physical origins: accreted and stripped from massive satellites, dynamically heated by mergers from the bulge and/or disk in the main progenitor, and formed from star formation triggered during mergers. The mass of the hot inner stellar halo defined in this paper is a quantity that can be robustly obtained for real galaxies by applying a population-orbit superposition method to integral-field-unit spectroscopy data, out to a distance of $\sim2\,R_e$, which is possible with current observations. Hence, this paper shows that integral-field-unit observations and dynamical models of the inner regions of galaxies provide a way to quantitatively determine the mass of ancient accreted satellites.

astro-ph.GA↗

arXiv2022

The MUSE Hubble Ultra Deep Field Survey XVI. The angular momentum of low-mass star-forming galaxies. A cautionary tale and insights from TNG50

We investigate the specific angular momentum (sAM) $ j(<r)$ profiles of intermediate redshift ($0.4<z<1.4$) star-forming galaxies (SFGs) in the relatively unexplored regime of low masses (down to $M_\star\sim 10^8$M$_{\odot}$), and small sizes (down to $R_{\rm e}\sim 1.5$ kpc) and characterize the sAM scaling relation and its redshift evolution. We have developed a 3D methodology to constrain sAM profiles of the star-forming gas using a forward modeling approach with \galpak{} that incorporates the effects of beam smearing, yielding the intrinsic morpho-kinematic properties even with limited spatial resolution data. Using mock observations from the TNG50 simulation, we find that our 3D methodology robustly recovers the star formation rate (SFR)-weighted $j(<r)$ profiles down to low effective signal-to-noise ratio (SNR) of $\gtrapprox3$. We applied our methodology blindly to a sample of 494 \OII{}-selected SFGs in the MUSE Ultra Deep Field (UDF) 9~arcmin$^2$ mosaic data, covering the unexplored $8<\log M_*/$M$_{\odot}<9$ mass range. We find that the (SFR-weighted) sAM relation follows $j\propto M_\star^α$ with an index $α$ varying from $α=0.3$ to $α=0.5$, from $\log M_\star/$M$_{\odot}=8$ to $\log M_*/$M$_{\odot}=10.5$. The UDF sample supports a redshift evolution consistent with the $(1+z)^{-0.5}$ expectation from a Universe in expansion. The scatter of the sAM sequence is a strong function of the dynamical state with $\log j|_{M_*}\propto 0.65 \times \log(V_{\rm max}/σ)$ where $σ$ is the velocity dispersion at $2 R_{\rm e}$. In TNG50, SFGs also form a $j-M_{\star}-(V/σ)$ plane but it correlates more with galaxy size than with morphological parameters. Our results suggest that SFGs might experience a dynamical transformation before their morphological transformation to becoming passive via either merging or secular evolution.

astro-ph.GA↗

arXiv2021

On the formation of massive quiescent galaxies with diverse morphologies in the TNG50 simulation

Observations have shown that the star-formation activity and the morphology of galaxies are closely related, but the underlying physical connection is not well understood. Using the TNG50 simulation, we explore the quenching and the morphological evolution of the 102 massive quiescent galaxies in the mass range of $10.5<\log(M_{\rm stellar}/M_{\odot})<11.5$ selected at $z=0$. The morphology of galaxies is quantified based on their kinematics, and we measure the quenching timescale of individual galaxies directly from star formation history. We show that galaxies tend to be quenched more rapidly if they: (i) are satellites in massive halos, (ii) have lower star-forming gas fractions, or (iii) inject a larger amount of black hole kinetic feedback energy. By following the global evolutionary pathways, we conclude that quiescent discs are mainly disc galaxies that are recently and slowly quenched. Approximately half of the quiescent ellipticals at $z=0$ are rapidly quenched at higher redshifts while still disc-like. While being quiescent, they gradually become more elliptical mostly by disc heating, yet these ellipticals still retain some degree of rotation. The other half of quiescent ellipticals with the most random motion-dominated kinematics build up large spheroidal components before quenching primarily by mergers, or in some cases, misaligned gas accretion. However, the mergers that contribute to morphological transformation do not immediately quench galaxies in many cases. In summary, we find that quenching and morphological transformation are decoupled. We conclude that the TNG black hole feedback -- in combination with the stochastic merger history of galaxies -- leads to a large diversity of quenching timescales and a rich morphological landscape.

astro-ph.GA↗

arXiv2021

High and low Sérsic index bulges in Milky Way- and M31-like galaxies: origin and connection to the bar with TNG50

We study bulge formation in MW/M31-like galaxies in a $Λ$-cold dark matter scenario, focusing on the origin of high- and low-Sersic index bulges. For this purpose we use TNG50, a simulation of the IllustrisTNG project that combines a resolution of $\sim 8 \times 10^4 M_{\odot}$ in stellar particles with a cosmological volume 52 cMpc in extent. We parametrize bulge surface brightness profiles by the Sérsic index and the bulge-to-total (B/T) ratio obtained from two-component photometric decompositions. In our sample of 287 MW/M31-like simulated galaxies, $17.1\%$ of photometric bulges exhibit high-Sérsic indices and $82.9\%$ show low-Sérsic indices. We study the impact that the environment, mergers and bars have in shaping the surface brightness profiles. We explore two different definitions for local environment and find no correlation between bulge properties and the environment where they reside. Simulated galaxies with higher Sérsic indices show, on average, a higher fraction of ex-situ stars in their kinematically selected bulges. For this bulge population the last significant merger (total mass ratio $m_{\rm sat}/m_{\rm host} > 0.1$) occurs, on average, at later times. However, a substantial fraction of low-Sérsic index bulges also experience a late significant merger. We find that bars play an important role in the development of the different types of photometric bulges. We show that the fraction of simulated galaxies with strong bars is smaller for the high- than for the low-Sérsic index population, reaching differences of $20\%$ at $z > 1$. Simulated galaxies with high fractions of ex-situ stars in the bulge do not develop strong bars. Conversely, simulated galaxies with long-lived strong bars have bulges with ex-situ fractions, $f_{\rm ex-situ} < 0.2$.

astro-ph.GA↗

arXiv2021

Bringing faint active galactic nuclei (AGNs) to light: a view from large-scale cosmological simulations

The sensitivity of X-ray facilities and our ability to detect fainter active galactic nuclei (AGNs) will increase with the upcoming Athena mission and the AXIS and Lynx concept missions, thus improving our understanding of supermassive black holes (BHs) in a luminosity regime that can be dominated by X-ray binaries. We analyze the population of faint AGN (L_x (2-10 keV) < 10^42 erg/s) in the Illustris, TNG100, EAGLE, and SIMBA cosmological simulations, and find that the properties of their host galaxies vary from one simulation to another. In Illustris and EAGLE, faint AGN are powered by low-mass BHs located in low-mass star-forming galaxies. In TNG100 and SIMBA, they are mostly associated with more massive BHs in quenched massive galaxies. We model the X-ray binary populations (XRB) of the simulated galaxies, and find that AGN often dominate the galaxy AGN+XRB hard X-ray luminosity at z>2, while XRBs dominate in some simulations at z<2. Whether the AGN or XRB emission dominates in star-forming and quenched galaxies depends on the simulations. These differences in simulations can be used to discriminate between galaxy formation models with future high-resolution X-ray observations. We compare the luminosity of simulated faint AGN host galaxies to observations of stacked galaxies from Chandra. Our comparison indicates that the simulations post-processed with our X-ray modeling tend to overestimate the AGN+XRB X-ray luminosity; luminosity that can be strongly affected by AGN obscuration. Some simulations reveal clear AGN trends as a function of stellar mass (e.g., galaxy luminosity drop in massive galaxies), which are not apparent in the observations.

astro-ph.GA↗

arXiv2021

Supermassive black holes in cosmological simulations I: M_BH-M_star relation and black hole mass function

The past decade has seen significant progress in understanding galaxy formation and evolution using large-scale cosmological simulations. While these simulations produce galaxies in overall good agreement with observations, they employ different sub-grid models for galaxies and supermassive black holes (BHs). We investigate the impact of the sub-grid models on the BH mass properties of the Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA simulations, focusing on the M_BH-M_star relation and the BH mass function. All simulations predict tight M_BH-M_star relations, and struggle to produce the lowest (M_BH< 10^7.5 Msun) in galaxies of M_star~10^10.5-10^11.5 Msun. While the time evolution of the mean M_BH-M_star relation is mild (<1 dex in BH mass for 0 10^9 Msun in most of the simulations. The BH mass function is dominated by efficiently accreting BHs (log10 f_Edd >-2$) at high redshifts, and transitions progressively from the high-mass to the low-mass end to be governed by inactive BHs. The transition time and the contribution of active BHs are different among the simulations, and can be used to evaluate models against observations.

astro-ph.GA↗

arXiv2021

X-ray bubbles in the circumgalactic medium of TNG50 Milky Way- and M31-like galaxies: signposts of supermassive black hole activity

The TNG50 cosmological simulation produces X-ray emitting bubbles, shells, and cavities in the circumgalactic gas above and below the stellar disks of Milky Way- and Andromeda-like galaxies with morphological features reminiscent of the eROSITA and Fermi bubbles in the Galaxy. Two-thirds of the 198 MW/M31 analogues inspected in TNG50 at z=0 show one or more large-scale, coherent features of over-pressurized gas that impinge into the gaseous halo. Some of the galaxies include a succession of bubbles or shells of increasing size, ranging from a few to many tens of kpc. These are prominent in gas pressure, X-ray emission and gas temperature, and often exhibit sharp boundaries with typical shock Mach numbers of 2-4. The gas in the bubbles outflows with maximum (95th pctl) radial velocities of 100-1500 km/s. TNG50 bubbles expand with speeds as high as 1000-2000 km/s (about 1-2 kpc/Myr), but with a great diversity and with larger bubbles expanding at slower speeds. The bubble gas is at 10^6.4-7.2 K temperatures and is enriched to metallicities of 0.5-2 solar. In TNG50, the bubbles are a manifestation of episodic, kinetic, wind-like energy injections from the supermassive black holes at the galaxy centers that accrete at low Eddington ratios. According to TNG50, X-ray, and possibly gamma-ray, bubbles similar to those observed in the Milky Way should be a frequent feature of disk-like galaxies prior to, or on the verge of, being quenched. They should be within the grasp of eROSITA in the local Universe.

astro-ph.GA↗

arXiv2021

The physical origins and dominant emission mechanisms of Lyman-alpha halos: results from the TNG50 simulation in comparison to MUSE observations

Extended Lyman-alpha emission is now commonly detected around high redshift galaxies through stacking and even on individual basis. Despite recent observational advances, the physical origin of these Lyman-alpha halos (LAHs), as well as their relationships to galaxies, quasars, circumgalactic gas, and other environmental factors remains unclear. We present results from our new Lyman-alpha full radiative transfer code voroILTIS which runs directly on the unstructured Voronoi tessellation of cosmological hydrodynamical simulations. We make use of the TNG50 simulation and simulate LAHs from redshift $z=2$ to $z=5$, focusing on star-forming galaxies with $8.0 < \log_{10}{(M_\star/\rm{M}_\odot)} < 10.5$. While TNG50 does not directly follow ionizing radiation, it includes an on-the-fly treatment for active galactic nuclei and ultraviolet background radiation with self-shielding, which are important processes impacting the cooling and ionization of the gas. Based on this model, we present the predictions for the stacked radial surface brightness profiles of Ly$α$ as a function of galaxy mass and redshift. Comparison with data from the MUSE UDF at $z>3$ reveals a promising level of agreement. We measure the correlations of LAH size and central brightness with galaxy properties, finding that at the masses of $8.5 \leq \log_{10} \left(M_\star/\rm{M}_\odot\right) \leq 9.5$, physical LAH sizes roughly double from $z=2$ to $z=5$. Finally, we decompose the profiles into contributions from diffuse emission and scattered photons from star-forming regions. In our simulations, we find rescattered photons from star-forming regions to be the major source in observed LAHs. Unexpectedly, we find that the flattening of LAH profiles at large radii becomes dominated by photons originating from other nearby halos rather than diffuse emission itself.

astro-ph.GA↗

arXiv2021

Towards precise galaxy evolution: a comparison between spectral indices of $z\sim1$ galaxies in the IllustrisTNG simulation and the LEGA-C survey

We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated $D_n4000$ and EW(H$δ$) of galaxies with $10.5 \leq \log(M_\ast/M_\odot) \leq 11.5$ at $0.6 \leq z \leq 1.0$ to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small $D_n4000$ when compared to LEGA-C, while LEGA-C galaxies have larger EW(H$δ$) at fixed $D_n4000$. There are several possible explanations: 1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger ($<1$~Gyr) stars, while TNG100 galaxies may not have such young sub-populations; 2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy formation simulations broadly reproduce the global age distribution of galaxies at $z\sim1$ and, at the same time, the high quality of the latest observed and simulated datasets help constrain stellar population synthesis models as well as the physical models underlying the simulations.

astro-ph.GA↗

arXiv2021

The abundance of satellites around Milky Way- and M31-like galaxies with the TNG50 simulation: a matter of diversity

We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final instalment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as disky galaxies with stellar masses of Mstar = 10^10.5-11.2 Msun in relative isolation at z = 0. By defining satellites as galaxies with Mstar > 5*10^6 Msun within 300 kpc (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median (16th - 84th percentiles) TNG50 MW/M31-like galaxy hosts a total of 5 (2-11) satellites with Mstar > 5*10^6 Msun, reaching up to Mstar ~ 10^8.5 Msun (10^7.4-9.4 Msun). The abundance of subhaloes with Mdyn > 5*10^7 Msun is larger by a factor of more than 10. The number of all satellites (subhaloes) ever accreted is larger by a factor of 4-5 (3-5) than those surviving to z = 0. Hosts with larger galaxy stellar mass, brighter K-band luminosity, larger total halo mass, and more recent halo assembly typically have a larger number of surviving satellites. The satellite abundances around TNG50 MW/M31-like galaxies are consistent with similar hosts from observational surveys (e.g. SAGA) and previous simulations (e.g. Latte). While the observed MW satellite system falls within the TNG50 scatter across all stellar masses considered, M31 is slightly more satellite-rich than our 1 sigma scatter, possibly due to volume and mass limitations. We find a handful of systems with both a Large and a Small Magellanic Cloud-like satellite. There is no missing satellites problem with TNG50.

astro-ph.GA↗