Astrophysicist

Category: Publications (Page 3 of 5)

Torrey et al. (2019)

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]

Habouzit et al. (2019)

Linking galaxy structural properties and star formation activity to black hole activity with IllustrisTNG

by
Habouzit, Mélanie; Genel, Shy; Somerville, Rachel S.; Kocevski, Dale; Hirschmann, Michaela; Dekel, Avishai; Choi, Ena; Nelson, Dylan; Pillepich, Annalisa; Torrey, Paul; Hernquist, Lars; Vogelsberger, Mark; Weinberger, Rainer; Springel, Volker

abstract
We study the connection between active galactic nuclei (AGN) and their host galaxies through cosmic time in the large-scale cosmological IllustrisTNG simulations. We first compare BH properties, i.e. the hard X-ray BH luminosity function, AGN galaxy occupation fraction, and distribution of Eddington ratios, to available observational constraints. The simulations produce a population of BHs in good agreement with observations, but we note an excess of faint AGN in hard X-ray (L_x̃ 10^{43-44} erg/s), and a lower number of bright AGN (L_x\gt 10^{44} erg/s), a conclusion that varies quantitatively but not qualitatively with BH luminosity estimation method. The lower Eddington ratios of the 109 M_{\odot } BHs compared to observations suggest that AGN feedback may be too efficient in this regime. We study galaxy star formation activity and structural properties, and design sample-dependent criteria to identify different galaxy types (star-forming/quiescent, extended/compact) that we apply both to the simulations and observations from the CANDELS fields. We analyse how the simulated and observed galaxies populate the specific star formation rate – stellar mass surface density diagram. A large fraction of the z = 0 M_{\star }≥slant 10^{11} M_{\odot } quiescent galaxies first experienced a compaction phase (i.e. reduction of galaxy size) while still forming stars, and then a quenching event. We measure the dependence of AGN fraction on galaxies’ locations in this diagram. After correcting the simulations with a redshift and AGN luminosity-dependent model for AGN obscuration, we find good qualitative and quantitative agreement with observations. The AGN fraction is the highest among compact star-forming galaxies (16-20{{ per cent}} at z ̃ 1.5-2), and the lowest among compact quiescent galaxies (6-10{{ per cent}} at z ̃ 1.5-2).

published in
Monthly Notices of the Royal Astronomical Society, Volume 484, Issue 4, p.4413-4443, April 2019

links to paper
[ADS][arXiv]

Stevens et al. (2019)

Atomic hydrogen in IllustrisTNG galaxies: the impact of environment parallelled with local 21-cm surveys

by
Stevens, Adam R. H.; Diemer, Benedikt; Lagos, Claudia del P.; Nelson, Dylan; Pillepich, Annalisa; Brown, Toby; Catinella, Barbara; Hernquist, Lars; Weinberger, Rainer; Vogelsberger, Mark; Marinacci, Federico

abstract
We investigate the influence of environment on the cold-gas properties of galaxies at z = 0 within the TNG100 cosmological, magnetohydrodynamic simulation, part of the IllustrisTNG suite. We extend previous post-processing methods for breaking gas cells into their atomic and molecular phases, and build detailed mocks to comprehensively compare to the latest surveys of atomic hydrogen (H I) in nearby galaxies, namely ALFALFA and xGASS. We use TNG100 to explore the H I content, star formation activity, and angular momentum of satellite galaxies, each as a function of environment, and find that satellites are typically a factor of ≳3 poorer in H I than centrals of the same stellar mass, with the exact offset depending sensitively on parent halo mass. Due to the large physical scales on which H I measurements are made (̃45-245 kpc), contributions from gas not bound to the galaxy of interest but in the same line of sight crucially lead to larger H I mass measurements in the mocks in many cases, ultimately aligning with observations. This effect is mass-dependent and naturally greater for satellites than centrals, as satellites are never isolated by definition. We also show that H I stripping in TNG100 satellites is closely accompanied by quenching, in tension with observational data that instead favour that H I is preferentially stripped before star formation is reduced.

published in
Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 4, p.5334-5354, March 2019

links to paper
[ADS][arXiv]

Rodriguez-Gomez et al. (2019)

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]

Yun et al. (2019)

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]

Ehlert et al. (2019)

The Sunyaev-Zel’dovich Effect of Simulated Jet-inflated Bubbles in Clusters

by
Ehlert, Kristian; Pfrommer, Christoph; Weinberger, Rainer; Pakmor, Rüdiger; Springel, Volker

abstract
Feedback by active galactic nuclei (AGNs) is essential for regulating the fast radiative cooling of low-entropy gas at the centers of galaxy clusters and for reducing star formation rates of central ellipticals. The details of self-regulation depend critically on the unknown contents of AGN-inflated bubbles. Observations of the Sunyaev-Zeldovich (SZ) signal of AGN bubbles provide us with the ability to directly measure the lobe electron pressure given a bubble morphology. Here we compute the SZ signal of jet-inflated bubbles in three-dimensional magnetohydrodynamical simulations of the galaxy cluster MS0735.6+7421 with the Arepo code, and compare our synthetic SZ results to inferences obtained with popular modeling approaches. We find that cutting out ellipsoidal bubbles from a double-beta pressure profile only matches the inner bubble edges in the simulations and fails to account for the emission of the shock-enhanced pressure cocoon outside the bubbles. This additional contribution significantly worsens the accuracy of the cut-out method for jets with small inclinations with respect to the line of sight. Also, the kinetic SZ effect of the bubbles, a previously neglected contribution, becomes relevant at these smaller inclinations due to entrainment and mixing of the intracluster medium with low-density jet material. Fortunately, the different signs of the kinetic SZ signal in opposite lobes allow this effect to be modeled. We present an approximate method to determine the jet inclination, which combines jet power and lifetime estimates, the stand-off distance between jet head and bow shock, and the kinetic SZ effect, thereby helping to correctly infer the bubble contents.

published in
The Astrophysical Journal Letters, Volume 872, Issue 1, article id. L8, 6 pp. (February 2019)

link to paper
[ADS][arXiv]

Genel et al. (2019)

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]

Ehlert et al. (2018)

Simulations of the dynamics of magnetized jets and cosmic rays in galaxy clusters

by
Ehlert, K.; Weinberger, R.; Pfrommer, C.; Pakmor, R.; Springel, V.

abstract
Feedback processes by active galactic nuclei in the centres of galaxy clusters appear to prevent large-scale cooling flows and impede star formation. However, the detailed heating mechanism remains uncertain. One promising heating scenario invokes the dissipation of Alfvén waves that are generated by streaming cosmic rays (CRs). In order to study this idea, we use three-dimensional magnetohydrodynamical simulations with the AREPO code that follow the evolution of jet-inflated bubbles that are filled with CRs in a turbulent cluster atmosphere. We find that a single injection event produces the CR distribution and heating rate required for a successful CR heating model. As a bubble rises buoyantly, cluster magnetic fields drape around the leading interface and are amplified to strengths that balance the ram pressure. Together with helical magnetic fields in the bubble, this initially confines the CRs and suppresses the formation of interface instabilities. But as the bubble continues to rise, bubble-scale eddies significantly amplify radial magnetic filaments in its wake and enable CR transport from the bubble to the cooling intracluster medium. By varying the jet parameters, we obtain a rich and diverse set of jet and bubble morphologies ranging from Fanaroff-Riley type I-like (FRI) to FRII-like jets. We identify jet energy as the leading order parameter (keeping the ambient density profiles fixed), whereas jet luminosity is primarily responsible for setting the Mach numbers of shocks around FRII-like sources. Our simulations also produce FRI-like jets that inflate bubbles without detectable shocks and show morphologies consistent with cluster observations.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 3, p.2878-2900, December 2018

links to paper
[ADS][arXiv]

Lovell et al. (2018)

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]

Barnes et al. (2018)

A census of cool-core galaxy clusters in IllustrisTNG

by
Barnes, David J.; Vogelsberger, Mark; Kannan, Rahul; Marinacci, Federico; Weinberger, Rainer; Springel, Volker; Torrey, Paul; Pillepich, Annalisa; Nelson, Dylan; Pakmor, Rüdiger; Naiman, Jill; Hernquist, Lars; McDonald, Michael

abstract
The thermodynamic structure of hot gas in galaxy clusters is sensitive to astrophysical processes and typically difficult to model with galaxy formation simulations. We explore the fraction of cool-core (CC) clusters in a large sample of 370 clusters from IllustrisTNG, examining six common CC definitions. IllustrisTNG produces continuous CC criteria distributions, the extremes of which are classified as CC and non-cool core (NCC), and the criteria are increasingly correlated for more massive clusters. At z = 0, the CC fractions for two criteria are in reasonable agreement with the observed fractions but the other four CC fractions are lower than observed. This result is partly driven by systematic differences between the simulated and observed gas fraction profiles. The simulated CC fractions with redshift show tentative agreement with the observed fractions, but linear fits demonstrate that the simulated evolution is steeper than observed. The conversion of CCs to NCCs appears to begin later and act more rapidly in the simulations. Examining the fraction of CCs and NCCs defined as relaxed we find no evidence that CCs are more relaxed, suggesting that mergers are not solely responsible for disrupting CCs. A comparison of the median thermodynamic profiles defined by different CC criteria shows that the extent to which they evolve in the cluster core is dependent on the CC criteria. We conclude that the thermodynamic structure of galaxy clusters in IllustrisTNG shares many similarities with observations, but achieving better agreement most likely requires modifications of the underlying galaxy formation model.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, p.1809-183, December 2018

links to paper
[ADS][arXiv]

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