Astrophysicist

# Category: galaxy formation and evolution(Page 2 of 4)

### First results from the TNG50 simulation: the evolution of stellar and gaseous discs across cosmic time

by
Pillepich, Annalisa; Nelson, Dylan; Springel, Volker; Pakmor, Rüdiger; Torrey, Paul; Weinberger, Rainer; Vogelsberger, Mark; Marinacci, Federico; Genel, Shy; van der Wel, Arjen; Hernquist, Lars

abstract
We present a new cosmological, magnetohydrodynamical simulation for galaxy formation: TNG50, the third and final instalment of the IllustrisTNG project. TNG50 evolves 2 × 21603 dark matter particles and gas cells in a volume 50 comoving Mpc across. It hence reaches a numerical resolution typical of zoom-in simulations, with a baryonic element mass of 8.5× 10^4 M_{\odot } and an average cell size of 70-140 pc in the star-forming regions of galaxies. Simultaneously, TNG50 samples ∼700 (6500) galaxies with stellar masses above 10^{10} (10^8) M_{\odot } at z = 1. Here we investigate the structural and kinematical evolution of star-forming galaxies across cosmic time (0 ≲ z ≲ 6). We quantify their sizes, disc heights, 3D shapes, and degree of rotational versus dispersion-supported motions as traced by rest-frame V-band light (i.e. roughly stellar mass) and by H α light (i.e. star-forming and dense gas). The unprecedented resolution of TNG50 enables us to model galaxies with sub-kpc half-light radii and with ≲300-pc disc heights. Coupled with the large-volume statistics, we characterize a diverse, redshift- and mass-dependent structural and kinematical morphological mix of galaxies all the way to early epochs. Our model predicts that for star-forming galaxies the fraction of disc-like morphologies, based on 3D stellar shapes, increases with both cosmic time and galaxy stellar mass. Gas kinematics reveal that the vast majority of 10^{9-11.5} M_{\odot } star-forming galaxies are rotationally supported discs for most cosmic epochs (Vrot/σ > 2-3, z ≲ 5), being dynamically hotter at earlier epochs (z ≳ 1.5). Despite large velocity dispersion at high redshift, cold and dense gas in galaxies predominantly arranges in disky or elongated shapes at all times and masses; these gaseous components exhibit rotationally dominated motions far exceeding the collisionless stellar bodies.

published in
Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 3, p.3196-3233, December 2019

links to paper
[ADS][arXiv]

### A study of stellar orbit fractions: simulated IllustrisTNG galaxies compared to CALIFA observations

by
Xu, Dandan; Zhu, Ling; Grand, Robert; Springel, Volker; Mao, Shude; van de Ven, Glenn; Lu, Shengdong; Wang, Yougang; Pillepich, Annalisa; Genel, Shy; Nelson, Dylan; Rodriguez-Gomez, Vicente; Pakmor, Rüdiger; Weinberger, Rainer; Marinacci, Federico; Vogelsberger, Mark; Torrey, Paul; Naiman, Jill; Hernquist, Lars

abstract
Motivated by the recently discovered kinematic Hubble sequence’ shown by the stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a comparable galaxy sample at z = 0 with a stellar mass range of M_{*}/M_{\odot }\in [10^{9.7}, 10^{11.4}] selected from the IllustrisTNG simulation and study their stellar orbit compositions in relation to a number of other fundamental galaxy properties. We find that the TNG100 simulation broadly reproduces the observed fractions of different orbital components and their stellar mass dependences. In particular, the mean mass dependences of the luminosity fractions for the kinematically warm and hot orbits are well reproduced within model uncertainties of the observed galaxies. The simulation also largely reproduces the observed peak and trough features at M_{*}≈ 1{-}2× 10^{10} M_{\odot } in the mean distributions of the cold- and hot-orbit fractions, respectively, indicating fewer cooler orbits and more hotter orbits in both more- and less-massive galaxies beyond such a mass range. Several marginal disagreements are seen between the simulation and observations: the average cold-orbit (counter-rotating) fractions of the simulated galaxies below (above) M_{*}≈ 6× 10^{10} M_{\odot } are systematically higher than the observational data by ≲ 10{{ per cent}} (absolute orbital fraction); the simulation also seems to produce more scatter for the cold-orbit fraction and less so for the non-cold orbits at any given galaxy mass. Possible causes that stem from the adopted heating mechanisms are discussed.

published in
Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 1, p.842-854, October 2019

links
[ADS][arXiv]

### The star formation activity of IllustrisTNG galaxies: main sequence, UVJ diagram, quenched fractions, and systematics

by
Donnari, Martina; Pillepich, Annalisa; Nelson, Dylan; Vogelsberger, Mark; Genel, Shy; Weinberger, Rainer; Marinacci, Federico; Springel, Volker; Hernquist, Lars

abstract
We select galaxies from the IllustrisTNG hydrodynamical simulations (M_stars> 10^9 M_☉ at 0 ≤ z ≤ 2) and characterize the shapes and evolutions of their UVJ and star formation rate-stellar mass (SFR-Mstars) diagrams. We quantify the systematic uncertainties related to different criteria to classify star-forming versus quiescent galaxies, different SFR estimates, and by accounting for the star formation measured within different physical apertures. The TNG model returns the observed features of the UVJ diagram at z ≤ 2, with a clear separation between two classes of galaxies. It also returns a tight star-forming main sequence (MS) for M_stars< 10^{10.5} (M_☉) with a ̃0.3 dex scatter at z ̃ 0 in our fiducial choices. If a UVJ-based cut is adopted, the TNG MS exhibits a downwardly bending at stellar masses of about 1010.5-10.7 M. Moreover, the model predicts that {̃ }80 (50) per cent of 1010.5-11 Mgalaxies at z = 0 (z = 2) are quiescent and the numbers of quenched galaxies at intermediate redshifts and high masses are in better agreement with observational estimates than previous models. However, shorter SFR-averaging time-scales imply higher normalizations and scatter of the MS, while smaller apertures lead to underestimating the galaxy SFRs: overall we estimate the inspected systematic uncertainties to sum up to about 0.2-0.3 dex in the locus of the MS and to about 15 percentage points in the fraction of quenched galaxies. While TNG colour distributions are clearly bimodal, this is not the case for the SFR logarithmic distributions in bins of stellar mass (SFR ≳ 10-3Myr-1). Finally, the slope and z = 0 normalization of the TNG MS are consistent with observational findings; however, the locus of the TNG MS remains lower by about 0.2-0.5 dex at 0.75 ≤ z < 2 than the available observational estimates taken at face value.

published in
Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 4, p.4817-4840, June 2019

links to paper
[ADS][arXiv]

### Baryons in the Cosmic Web of IllustrisTNG – I: gas in knots, filaments, sheets, and voids

by
Martizzi, Davide; Vogelsberger, Mark; Artale, Maria Celeste; Haider, Markus; Torrey, Paul; Marinacci, Federico; Nelson, Dylan; Pillepich, Annalisa; Weinberger, Rainer; Hernquist, Lars; Naiman, Jill; Springel, Volker

abstract
We analyse the IllustrisTNG simulations to study the mass, volume fraction, and phase distribution of gaseous baryons embedded in the knots, filaments, sheets, and voids of the Cosmic Web from redshift z = 8 to redshift z = 0. We find that filaments host more star-forming gas than knots, and that filaments also have a higher relative mass fraction of gas in this phase than knots. We also show that the cool, diffuse intergalactic medium [IGM; T< 10^5 K, n_H< 10^{-4}(1+z) cm^{-3}] and the warm-hot intergalactic medium [WHIM; 10^5 < T< 10^7 K, n_H < 10^{-4}(1+z) cm^{-3}] constitute {̃ } 39 and {̃ } 46{{ per cent}} of the baryons at redshift z = 0, respectively. Our results indicate that the WHIM may constitute the largest reservoir of missing baryons at redshift z = 0. Using our Cosmic Web classification, we predict the WHIM to be the dominant baryon mass contribution in filaments and knots at redshift z = 0, but not in sheets and voids where the cool, diffuse IGM dominates. We also characterize the evolution of WHIM and IGM from redshift z = 4 to redshift z = 0, and find that the mass fraction of WHIM in filaments and knots evolves only by a factor of ̃2 from redshift z = 0 to 1, but declines faster at higher redshift. The WHIM only occupies 4-11 per cent of the volume at redshift 0 ≤ z ≤ 1. We predict the existence of a significant number of currently undetected O VII and Ne IX absorption systems in cosmic filaments, which could be detected by future X-ray telescopes like Athena.

published in
Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 3, p.3766-3787, July 2019

links to paper
[ADS][arXiv]

### The IllustrisTNG simulations: public data release

by
Nelson, Dylan; Springel, Volker; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Torrey, Paul; Genel, Shy; Vogelsberger, Mark; Pakmor, Ruediger; Marinacci, Federico; Weinberger, Rainer; Kelley, Luke; Lovell, Mark; Diemer, Benedikt; Hernquist, Lars

abstract
We present the full public release of all data from the 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 black holes from early time to the present day, z=0. Each of the flagship runs—TNG50, TNG100, and TNG300—are accompanied by halo/subhalo catalogs, merger trees, lower-resolution and dark-matter only counterparts, all available with 100 snapshots. We discuss scientific and numerical cautions and caveats relevant when using TNG. The data volume now directly accessible online is ̃750 TB, including 1200 full volume snapshots and ̃80,000 high time-resolution subbox snapshots. This will increase to ̃1.1 PB with the future release of TNG50. 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 enabling user computation with local access to TNG data, alleviating the need to download large datasets.

published in
Computational Astrophysics and Cosmology, Volume 6, Issue 1, article id. 2, 29 pp., May 2019

links to paper
[ADS][arXiv]

### The evolution of the mass-metallicity relation and its scatter in IllustrisTNG

by
Torrey, Paul; Vogelsberger, Mark; Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Nelson, Dylan; Naiman, Jill; Pillepich, Annalisa; Genel, Shy; Weinberger, Rainer; Hernquist, Lars

abstract
The coevolution of galaxies and their metal content serves as an important test for galaxy feedback models. We analyse the distribution and evolution of metals within the IllustrisTNG simulation suite with a focus on the gas-phase mass-metallicity relation (MZR). We find that the IllustrisTNG model broadly reproduces the slope and normalization evolution of the MZR across the redshift range 0 < z < 2 and mass range 109 < M*/M < 1010.5. We make predictions for the high-redshift (2 < z < 10) metal content of galaxies which is described by a gradual decline in the normalization of the metallicity with an average high-redshift (z > 2) evolution fit by d log(Z)/dz ≈ -0.064. Our simulations indicate that the metal retention efficiency of the interstellar medium (ISM) is low: a majority of gas-phase metals (̃85 per cent at z = 0) live outside of the ISM, either in an extended gas disc, the circumgalactic medium, or outside the halo. Nevertheless, the redshift evolution in the simulated MZR normalization is driven by the higher gas fractions of high-redshift galaxies, not by changes to the metal retention efficiency. The scatter in the simulated MZR contains a clear correlation with the gas-mass or star formation rate of the system, in agreement with the observed fundamental metallicity relation. The scatter in the MZR is driven by a competition between periods of enrichment- and accretion-dominated metallicity evolution. We expect that while the normalization of the MZR declines with redshift, the slope of the correlation between metallicity and gas-mass at fixed stellar mass is not a strong function of redshift. Our results indicate that the gas fraction dependence of regulator’ style models allows them to simultaneously explaining the shape, redshift evolution, and existence of correlated scatter with gas fraction about the MZR.

published in
Monthly Notices of the Royal Astronomical Society, Volume 484, Issue 4, p.5587-5607, April 2019

links to paper
[ADS][arXiv]

### The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations

by
Rodriguez-Gomez, Vicente; Snyder, Gregory F.; Lotz, Jennifer M.; Nelson, Dylan; Pillepich, Annalisa; Springel, Volker; Genel, Shy; Weinberger, Rainer; Tacchella, Sandro; Pakmor, Rüdiger; Torrey, Paul; Marinacci, Federico; Vogelsberger, Mark; Hernquist, Lars; Thilker, David A.

abstract
We have generated synthetic images of ̃27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log10(M*/M) ≈ 9.8-11.3 galaxies at z ≈ 0.05. Most of our synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves. We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics – including the Gini-M20and concentration-asymmetry-smoothness statistics – and performs 2D Sérsic fits. Overall, we find that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation. In particular, the locus of the Gini-M20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the morphological, size and shape parameters considered in this work lie within the ̃1σ scatter of the observational trends. However, the IllustrisTNG model has some difficulty with more stringent tests, such as producing a strong morphology-colour relation. This results in a somewhat higher fraction of red discs and blue spheroids compared to observations. Similarly, the morphology-size relation is problematic: while observations show that discs tend to be larger than spheroids at a fixed stellar mass, such a trend is not present in IllustrisTNG.

published in
Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 3, p.4140-4159, March 2019

links to paper
[ADS][arXiv]

### Jellyfish galaxies with the IllustrisTNG simulations – I. Gas-stripping phenomena in the full cosmological context

by
Yun, Kiyun; Pillepich, Annalisa; Zinger, Elad; Nelson, Dylan; Donnari, Martina; Joshi, Gandhali; Rodriguez-Gomez, Vicente; Genel, Shy; Weinberger, Rainer; Vogelsberger, Mark; Hernquist, Lars

abstract
We use the IllustrisTNG simulations to study the demographics and properties of jellyfish galaxies in the full cosmological context. By jellyfish galaxies, we mean satellites orbiting in massive groups and clusters that exhibit highly asymmetric distributions of gas and gas tails. In particular, we select TNG100 galaxies at low redshifts (z ≤ 0.6) with stellar mass exceeding 10^{9.5} M_{☉} and with host halo masses in the range 10^{13} ≤ M_200c/ M_{☉}≤ 10^{14.6}. Among more than about 6000 (2600) galaxies with stars (and some gas), we identify 800 jellyfish galaxies by visually inspecting their gas and stellar mass maps in random projections. Namely, about 31 per cent of cluster satellites are found with signatures of ram-pressure stripping and gaseous tails stemming from their main luminous bodies. This is a lower limit: the random orientation entails a loss of about 30 per cent of galaxies that in an optimal projection would otherwise be identified as jellyfish. Furthermore, jellyfish galaxies are more frequent at intermediate and large cluster-centric distances (r/R200c ≳ 0.25), in more massive hosts and at smaller satellite masses, and they typically orbit supersonically. The gaseous tails usually extend in opposite directions to the galaxy trajectory, with no relation between tail orientation and position of the host’s centre. Finally, jellyfish galaxies are late infallers (<2.5-3 Gyr ago, at z = 0) and the emergence of gaseous tails correlates well with the presence of bow shocks in the intracluster medium.

published in
Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 1, p.1042-1066, February 2019

links to paper
[ADS][arXiv]

### A Quantification of the Butterfly Effect in Cosmological Simulations and Implications for Galaxy Scaling Relations

by
Genel, Shy; Bryan, Greg L.; Springel, Volker; Hernquist, Lars; Nelson, Dylan; Pillepich, Annalisa; Weinberger, Rainer; Pakmor, Rüdiger; Marinacci, Federico; Vogelsberger, Mark

abstract
We study the chaotic-like behavior of cosmological simulations by quantifying how minute perturbations grow over time and manifest as macroscopic differences in galaxy properties. When we run pairs of “shadow” simulations that are identical except for random minute initial displacements to particle positions (e.g., of order {10}-7 {pc}), the results diverge from each other at the individual galaxy level (while the statistical properties of the ensemble of galaxies are unchanged). After cosmological times, the global properties of pairs of “shadow” galaxies that are matched between the simulations differ from each other, generally at a level of ̃2-25%, depending on the considered physical quantity. We perform these experiments using cosmological volumes of {(25{–}50{Mpc}/h)}3evolved either purely with dark matter, or with baryons and star formation but no feedback, or else using the full feedback model of the IllustrisTNG project. The runs cover four resolution levels spanning a factor of 512 in mass. We find that, without feedback, the differences between shadow galaxies generally become smaller as the resolution increases—but with the IllustrisTNG model, the results mostly converge toward a “floor.” This hints at the role of feedback in setting the chaotic properties of galaxy formation. Importantly, we compare the macroscopic differences between shadow galaxies to the overall scatter in various galaxy scaling relations, and conclude that, for the star formation-mass and the Tully-Fisher relations, the butterfly effect in our simulations contributes significantly to the overall scatter. We find that our results are robust to whether random numbers are used in the subgrid models or not. We discuss the implications for galaxy formation theory in general and for cosmological simulations in particular.

published in
The Astrophysical Journal, Volume 871, Issue 1, article id. 21, 27 pp. (January 2019)

links to paper
[ADS][arXiv]

### The fraction of dark matter within galaxies from the IllustrisTNG simulations

by
Lovell, Mark R.; Pillepich, Annalisa; Genel, Shy; Nelson, Dylan; Springel, Volker; Pakmor, Rüdiger; Marinacci, Federico; Weinberger, Rainer; Torrey, Paul; Vogelsberger, Mark; Alabi, Adebusola; Hernquist, Lars

abstract
We use the IllustrisTNG (TNG) cosmological simulations to provide theoretical expectations for the dark matter mass fractions (DMFs) and circular velocity profiles of galaxies. TNG predicts flat circular velocity curves for z = 0 Milky Way (MW)-like galaxies beyond a few kpc from the galaxy centre, in better agreement with observational constraints than its predecessor, Illustris. TNG also predicts an enhancement of the dark matter mass within the 3D stellar half-mass radius (r_half; M_200c = 10^{10}-10^{13} M_{☉ }, z ≤ 2) compared to its dark matter only and Illustris counterparts. This enhancement leads TNG present-day galaxies to be dominated by dark matter within their inner regions, with f_DM(< r_half)≳ 0.5 at all masses and with a minimum for MW-mass galaxies. The 1σ scatter is ≲10 per cent at all apertures, which is smaller than that inferred by some observational data sets, e.g. 40 per cent from the SLUGGS survey. TNG agrees with the majority of the observationally inferred values for elliptical galaxies once a consistent initial mass function is adopted (Chabrier) and the DMFs are measured within the same apertures. The DMFs measured within r_half increase towards lower redshifts: this evolution is dominated by the increase in galaxy size with time. At z ̃ 2, the DMF in disc-like TNG galaxies decreases with increasing galaxy mass, with f_DM(< r_half) ̃ 0.10-0.65 for 1010 ≲ Mstars/M ≲ 1012, and are two times higher than if TNG galaxies resided in Navarro-Frenk-White dark matter haloes unaffected by baryonic physics. It remains to be properly assessed whether recent observational estimates of the DMFs at z ̃ 2 rule out the contraction of the dark matter haloes predicted by the TNG model.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, p.1950-1975, December 2018

links to paper
[ADS][arXiv]

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