Context.
Early-type galaxies (ETGs) are found to follow a wide variety of merger and accretion histories in cosmological simulations.
Aims.
We characterize the photometric and kinematic properties of ...simulated ETG stellar halos, and compare them to the observations.
Methods.
We selected a sample of 1114 ETGs in the TNG100 simulation and 80 in the higher-resolution TNG50. These ETGs span a stellar mass range of 10
10.3
− 10
12
M
⊙
and they were selected within the range of
g
−
r
colour and
λ
-ellipticity diagram populated by observed ETGs. We determined photometric parameters, intrinsic shapes, and kinematic observables in their extended stellar halos. We compared the results with central IFU kinematics and ePN.S planetary nebula velocity fields at large radii, studying the variation in kinematics from center to halo, and connecting it to a change in the intrinsic shape of the galaxies.
Results.
We find that the simulated galaxy sample reproduces the diversity of kinematic properties observed in ETG halos. Simulated fast rotators (FRs) divide almost evenly in one third having flat
λ
profiles and high halo rotational support, a third with gently decreasing profiles, and another third with low halo rotation. However, the peak of rotation occurs at larger
R
than in observed ETG samples. Slow rotators (SRs) tend to have increased rotation in the outskirts, with half of them exceeding
λ
= 0.2. For
M
*
> 10
11.5
M
⊙
halo rotation is unimportant. A similar variety of properties is found for the stellar halo intrinsic shapes. Rotational support and shape are deeply related: the kinematic transition to lower rotational support is accompanied by a change towards rounder intrinsic shape. Triaxiality in the halos of FRs increases outwards and with stellar mass. Simulated SRs have relatively constant triaxiality profiles.
Conclusions.
Simulated stellar halos show a large variety of structural properties, with quantitative but no clear qualitative differences between FRs and SRs. At the same stellar mass, stellar halo properties show a more gradual transition and significant overlap between the two families, despite the clear bimodality in the central regions. This is in agreement with observations of extended photometry and kinematics.
ABSTRACT
We present a comparison of the physical properties of the ionized gas in the circumgalactic medium and intergalactic medium (IGM) at z ∼ 0 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 Planck CMB maps with haloes and large-scale structure. 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 profile. Instead, we present a new model with a mass-dependent shape that fits the profiles accurately.
ABSTRACT Long dynamical timescales in the outskirts of galaxies preserve the information content of their accretion histories, for example in the form of stellar population gradients. We present a ...detailed analysis of the stellar halo properties of a statistically representative sample of early-type galaxies from the Illustris simulation, and show that stellar population gradients at large radii can indeed be used to infer basic properties of galactic accretion histories. We measure metallicity, age, and surface-brightness profiles in quiescent Illustris galaxies ranging from = 1010-2 × 1012 and show that they are in reasonable agreement with observations. At fixed mass, galaxies that accreted little of their stellar halo material tend to have steeper metallicity and surface-brightness profiles, between 2-4 effective radii ( ), than those with larger accreted fractions. Profiles of metallicity and surface-brightness in the stellar halo typically flatten from z = 1 to the present. This suggests that the accretion of stars into the stellar halo tends to flatten metallicity and surface-brightness profiles, a picture which is supported by the tight correlation between the two gradients in the stellar halo. We find no statistical evidence of additional information content related to accretion histories in stellar halo metallicity profiles, beyond what is contained in surface-brightness profiles. Age gradients in the stellar halo do not appear to be sensitive to galactic accretion histories, and none of the stellar population gradients studied are strongly correlated with the mean merger mass-ratio. Our findings relate specifically to regions of the stellar halo within 4 , but suggest that future observations that reach large radii outside galaxies (including to 10 and beyond) will have the best potential to constrain galactic accretion histories.
We present a machine-learning (ML) approach for estimating galaxy cluster masses from Chandra mock images. We utilize a Convolutional Neural Network (CNN), a deep ML tool commonly used in image ...recognition tasks. The CNN is trained and tested on our sample of 7896 Chandra X-ray mock observations, which are based on 329 massive clusters from the simulation. Our CNN learns from a low resolution spatial distribution of photon counts and does not use spectral information. Despite our simplifying assumption to neglect spectral information, the resulting mass values estimated by the CNN exhibit small bias in comparison to the true masses of the simulated clusters (−0.02 dex) and reproduce the cluster masses with low intrinsic scatter, 8% in our best fold and 12% averaging over all. In contrast, a more standard core-excised luminosity method achieves 15%-18% scatter. We interpret the results with an approach inspired by Google DeepDream and find that the CNN ignores the central regions of clusters, which are known to have high scatter with mass.
Stellar halos in early-type galaxies (ETGs) are shaped by their accretion and merger histories. We use a sample of 1114 ETGs in the TNG100 simulation of the IllustrisTNG suite with stellar masses ...1010.3 ≤ M*/M⊙ ≤ 1012, selected at z = 0 within the range of the g − r colour and λ-ellipticity diagram populated by observed ETGs. We study how the rotational support and intrinsic shapes of the stellar halos depend on the fraction of stars accreted, both overall and separately, by major, minor, and mini mergers. Accretion histories in TNG100 ETGs as well as the final radial distributions of ex-situ stars fexsitu(R) relative to in-situ (“accretion classes”) strongly correlate with stellar mass. Low-mass galaxies have characteristic peaked rotation profiles and near-oblate shapes with rounder halos that are completely driven by the in-situ stars. At high fexsitu, major mergers decrease the in-situ peak in rotation velocity, flatten the V*/σ*(R) profiles, and increase the triaxiality of the stellar halos. Kinematic transition radii do not trace the transition between in-situ- and ex-situ-dominated regions, but for systems with M* > 1010.6 M⊙ the local rotational support of the stellar halos decreases with the local ex-situ fraction fexsitu(R) at fixed M*, and their triaxiality increases with fexsitu(R). These correlations between rotational support, intrinsic shapes, and local fexsitu are followed by fast and slow rotators alike with a continuous and overlapping sequence of properties, but slow rotators are concentrated at the high-fexsitu end dominated by dry major mergers. We find that in ∼20% of high-mass ETGs, the central regions are dominated by stars from a high-redshift compact progenitor. Merger events dynamically couple stars and dark matter: in high-mass galaxies and at large radii where fexsitu ≳ 0.5, both components tend to have similar intrinsic shapes and rotational support, and nearly aligned principal axes and spin directions. Based on these results we suggest that extended photometry and kinematics of massive ETGs (M* > 1010.6 M⊙) can be used to estimate the local fraction of ex-situ stars, and to approximate the intrinsic shapes and rotational support of the co-spatial dark matter component.
We present the full public release of all data from the Illustris simulation project. Illustris is a suite of large volume, cosmological hydrodynamical simulations run with the moving-mesh code Arepo ...and including a comprehensive set of physical models critical for following the formation and evolution of galaxies across cosmic time. Each simulates a volume of (106.5 Mpc)3 and self-consistently evolves five different types of resolution elements from a starting redshift of z=127 to the present day, z=0. These components are: dark matter particles, gas cells, passive gas tracers, stars and stellar wind particles, and supermassive black holes. This data release includes the snapshots at all 136 available redshifts, halo and subhalo catalogs at each snapshot, and two distinct merger trees. Six primary realizations of the Illustris volume are released, including the flagship Illustris-1 run. These include three resolution levels with the fiducial “full” baryonic physics model, and a dark matter only analog for each. In addition, we provide four distinct, high time resolution, smaller volume “subboxes”. The total data volume is ∼265 TB, including ∼800 full volume snapshots and ∼30,000 subbox snapshots. We describe the released data products as well as tools we have developed for their analysis. All data may be directly downloaded in its native HDF5 format. Additionally, we release a comprehensive, web-based API which allows programmatic access to search and data processing tasks. In both cases we provide example scripts and a getting-started guide in several languages: currently, IDL, Python, and Matlab. This paper addresses scientific issues relevant for the interpretation of the simulations, serves as a pointer to published and on-line documentation of the project, describes planned future additional data releases, and discusses technical aspects of the release.
ABSTRACT
We study how mock-observed stellar morphological and structural properties of massive galaxies are built up between $z$ = 0.5 and $z$ = 3 in the TNG50 cosmological simulation. We generate ...mock images with the properties of the CANDELS survey and derive Sersic parameters and optical rest-frame morphologies as usually done in the observations. Overall, the simulation reproduces the observed evolution of the abundances of different galaxy morphological types of star-forming and quiescent galaxies. The log M* − log Re and log M* − log Σ1 relations of the simulated star-forming and quenched galaxies also match the observed slopes and zeropoints to within 1-σ. In the simulation, galaxies increase their observed central stellar mass density (Σ1) and transform in morphology from irregular/clumpy systems to normal Hubble-type systems in the star formation main sequence at a characteristic stellar mass of ∼1010.5 M⊙ which is reflected in an increase of the central stellar mass density (Σ1). This morphological transformation is connected to the activity of the central super massive black holes (SMBHs). At low stellar masses (109 < M*/M⊙ < 1010) SMBHs grow rapidly, while at higher mass SMBHs switch into the kinetic feedback mode and grow more slowly. During this low-accretion phase, SMBH feedback leads to the quenching of star-formation, along with a simultaneous growth in Σ1, partly due to the fading of stellar populations. More compact massive galaxies grow their SMBHs faster than extended ones of the same mass and end up quenching earlier. In the TNG50 simulation, SMBHs predominantly grow via gas accretion before galaxies quench, and Σ1 increases substantially after SMBH growth slows down. The simulation predicts therefore that quiescent galaxies have higher Σ1 values than star-forming galaxies for the same SMBH mass, which disagrees with alternative models, and may potentially be in tension with some observations.
Radio relics are diffuse synchrotron sources in the outskirts of merging galaxy clusters energized by the merger shocks. In this paper, we present an overview of the radio relics in massive cluster ...mergers identified in the new TNG-Cluster simulation. This is a suite of magnetohydrodynamical cosmological zoom-in simulations of 352 massive galaxy clusters with M 500c = 10 14.0 − 15.3 M ⊙ sampled from a 1 Gpc-sized cosmological box. The simulations were performed using the moving-mesh code AREPO with the galaxy formation model and high numerical resolution consistent with the TNG300 run of the IllustrisTNG series. We post-processed the shock properties obtained from the on-the-fly shock finder to estimate the diffuse radio emission generated by cosmological shockwaves for a total of ∼300 radio relics at redshift z = 0 − 1. TNG-Cluster returned a variety of radio relics with diverse morphologies, encompassing classical examples of double radio relics, single relics, and “inverted” radio relics that are convex to the cluster center. Moreover, the simulated radio relics reproduced both the abundance and statistical relations of observed relics. We find that extremely large radio relics (> 2 Mpc) are predominantly produced in massive cluster mergers with M 500c ≳ 8 × 10 14 M ⊙ . This underscores the significance of simulating massive mergers to study giant radio relics similar to those found in observations. We released a library of radio relics from the TNG-Cluster simulation, which will serve as a crucial reference for upcoming next-generation surveys.
ABSTRACT
We test cosmological hydrodynamical simulations of galaxy formation regarding the properties of the blue cloud (BC), green valley (GV), and red sequence (RS), as measured on the 4000Å break ...strength versus stellar mass plane at z = 0.1. We analyse the RefL0100N1504 run of EAGLE and the TNG100 run of IllustrisTNG project, by comparing them with the Sloan Digital Sky Survey (SDSS), while taking into account selection bias. Our analysis focuses on the GV, within stellar mass $\log \, \mathrm{{\it M}_\star /M_{\odot }} \simeq 10\!-\!11$, selected from the bimodal distribution of galaxies on the Dn(4000) versus stellar mass plane, following Angthopo et al. methodology. Both simulations match the fraction of AGN in the GV. However, they overproduce quiescent GV galaxies with respect to observations, with IllustrisTNG yielding a higher fraction of quiescent GV galaxies than EAGLE. In both, GV galaxies have older luminosity-weighted ages with respect to the SDSS, while a better match is found for mass-weighted ages. We find EAGLE GV galaxies quench their star formation early, but undergo later episodes of star formation, matching observations. In contrast, IllustrisTNG GV galaxies have a more extended star formation history, and quench more effectively at later cosmic times, producing the excess of quenched galaxies in GV compared with SDSS, based on the 4000Å break strength. These results suggest the AGN feedback subgrid physics, more specifically, the threshold halo mass for black hole input and the black hole seed mass, could be the primary cause of the overproduction of quiescent galaxies found with respect to the observational constraints.
We studied the effects of cluster environments on galactic structures by using the TNG50 cosmological simulation and observed galaxies in the Fornax cluster. We focused on galaxies with stellar ...masses of 10 8 − 12 M ⊙ at z = 0 that reside in Fornax-like clusters with total masses of M 200c = 10 13.4 − 14.3 M ⊙ . We characterized the stellar structures by decomposing each galaxy into a dynamically cold disk and a hot non-disk component, and studied the evolution of both the stellar and gaseous constituents. In TNG50, we find that the cold (i.e., star-forming) gas is quickly removed when a galaxy falls into a Fornax-mass cluster. About 42%, 73%, and 87% of the galaxies have lost 80% of their star-forming gas at 1, 2, and 4 billion years after infall, respectively, with the remaining gas concentrating in the inner regions of the galaxy. The radius of the star-forming gaseous disk decreases to half its original size at 1, 2, and 4 billion years after infall for 7%, 27%, and 66% of the galaxies, respectively. As a result, star formation (SF) in the extended dynamically cold disk sharply decreases, even though a low level of SF persists at the center for a few additional gigayears. This leads to a tight correlation between the average stellar age in the dynamically cold disk and the infall time of galaxies. Furthermore, the luminosity fraction of the dynamically cold disk in ancient infallers (i.e., with an infall time ≳8 Gyr ago) is only about one-third of that in recent infallers (infall time ≲4 Gyr ago), controlling for galaxy stellar mass. This quantitatively agrees with what is observed in early-type galaxies in the Fornax cluster. Gas removal stops the possible growth of the disk, with gas removed earlier in galaxies that fell in earlier, and hence the cold-disk fraction is correlated with the infall time. The stellar disk can be significantly disrupted by tidal forces after infall, through a long-term process that enhances the difference among cluster galaxies with different infall times.
PDF
