We review the progress in modeling the galaxy population in hydrodynamical simulations of the ΛCDM cosmogony. State-of-the-art simulations now broadly reproduce the observed spatial clustering of ...galaxies; the distributions of key characteristics, such as mass, size, and SFR; and scaling relations connecting diverse properties to mass. Such improvements engender confidence in the insight drawn from simulations. Many important outcomes, however, particularly the properties of circumgalactic gas, are sensitive to the details of the subgrid models used to approximate the macroscopic effects of unresolved physics, such as feedback processes. We compare the outcomes of leading simulation suites with observations, and with each other, to identify the enduring successes they have cultivated and the outstanding challenges to be tackled with the next generation of models. Our key conclusions include the following:
ABSTRACT
We use the age–metallicity distribution of 96 Galactic globular clusters (GCs) to infer the formation and assembly history of the Milky Way (MW), culminating in the reconstruction of its ...merger tree. Based on a quantitative comparison of the Galactic GC population to the 25 cosmological zoom-in simulations of MW-mass galaxies in the E-MOSAICS project, which self-consistently model the formation and evolution of GC populations in a cosmological context, we find that the MW assembled quickly for its mass, reaching {25, 50} per cent of its present-day halo mass already at z = {3, 1.5} and half of its present-day stellar mass at z = 1.2. We reconstruct the MW’s merger tree from its GC age–metallicity distribution, inferring the number of mergers as a function of mass ratio and redshift. These statistics place the MW’s assembly rate among the 72th–94th percentile of the E-MOSAICS galaxies, whereas its integrated properties (e.g. number of mergers, halo concentration) match the median of the simulations. We conclude that the MW has experienced no major mergers (mass ratios >1:4) since z ∼ 4, sharpening previous limits of z ∼ 2. We identify three massive satellite progenitors and constrain their mass growth and enrichment histories. Two are proposed to correspond to Sagittarius (a few 108 M⊙) and the GCs formerly associated with Canis Major (${\sim }10^9\, \mbox{M$_\odot $}$). The third satellite has no known associated relic and was likely accreted between z = 0.6 and 1.3. We name this enigmatic galaxy Kraken and propose that it is the most massive satellite ($M_*\sim 2\times 10^9\, \mbox{M$_\odot $}$) ever accreted by the MW. We predict that ∼40 per cent of the Galactic GCs formed ex situ (in galaxies with masses M* = 2 × 107–$2\times 10^9\, \mbox{M$_\odot $}$), with 6 ± 1 being former nuclear clusters.
ABSTRACT
We introduce the Assembly of high-ResoluTion Eagle-simulations of MIlky Way-type galaxieS (artemis) simulations, a new set of 42 zoomed-in, high-resolution (baryon particle mass of $\approx ...2\times 10^4 \, {\rm M}_{\odot }\, h^{-1}$), hydrodynamical simulations of galaxies residing in haloes of Milky Way mass, simulated with the eagle galaxy formation code with re-calibrated stellar feedback. In this study, we analyse the structure of stellar haloes, specifically the mass density, surface brightness, metallicity, colour, and age radial profiles, finding generally very good agreement with recent observations of local galaxies. The stellar density profiles are well fitted by broken power laws, with inner slopes of ≈−3, outer slopes of ≈−4, and break radii that are typically ≈20–40 kpc. The break radii generally mark the transition between in situ formation and accretion-driven formation of the halo. The metallicity, colour, and age profiles show mild large-scale gradients, particularly when spherically averaged or viewed along the major axes. Along the minor axes, however, the profiles are nearly flat, in agreement with observations. Overall, the structural properties can be understood by two factors: that in situ stars dominate the inner regions and that they reside in a spatially flattened distribution that is aligned with the disc. Observations targeting both the major and minor axes of galaxies are thus required to obtain a complete picture of stellar haloes.
ABSTRACT
We examine the connection between the properties of the circumgalactic medium (CGM) and the quenching and morphological evolution of central galaxies in the EAGLE and IllustrisTNG ...simulations. The simulations yield very different median CGM mass fractions, fCGM, as a function of halo mass, M200, with low-mass haloes being significantly more gas-rich in IllustrisTNG than in EAGLE. Nonetheless, in both cases scatter in fCGM at fixed M200 is strongly correlated with the specific star formation rate and the kinematic morphology of central galaxies. The correlations are strongest for ∼L⋆ galaxies, corresponding to the mass scale at which AGN feedback becomes efficient. This feedback elevates the CGM cooling time, preventing gas from accreting on to the galaxy to fuel star formation, and thus establishing a preference for quenched, spheroidal galaxies to be hosted by haloes with low fCGM for their mass. In both simulations, fCGM correlates negatively with the host halo’s intrinsic concentration, and hence with its binding energy and formation redshift, primarily because early halo formation fosters the rapid early growth of the central black hole (BH). This leads to a lower fCGM at fixed M200 in EAGLE because the BH reaches high accretion rates sooner, whilst in IllustrisTNG it occurs because the central BH reaches the mass threshold at which AGN feedback is assumed to switch from thermal to kinetic injection earlier. Despite these differences, there is consensus from these state-of-the-art simulations that the expulsion of efficiently cooling gas from the CGM is a crucial step in the quenching and morphological evolution of central galaxies.
Galaxies fall into two clearly distinct types: 'blue-sequence' galaxies which are rapidly forming young stars, and 'red-sequence' galaxies in which star formation has almost completely ceased. Most ...galaxies more massive than ... follow the red sequence, while less massive central galaxies lie on the blue sequence. We show that these sequences are created by a competition between star formation-driven outflows and gas accretion on to the supermassive black hole at the galaxy's centre. We develop a simple analytic model for this interaction. In galaxies less massive than ..., young stars and supernovae drive a high-entropy outflow which is more buoyant than any tenuous corona. The outflow balances the rate of gas inflow, preventing high gas densities building up in the central regions. More massive galaxies, however, are surrounded by an increasingly hot corona. Above a halo mass of ..., the outflow ceases to be buoyant and star formation is unable to prevent the build-up of gas in the central regions. This triggers a strongly non-linear response from the black hole. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for star formation. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. We show that the analytic model provides a good description of galaxy evolution in the EAGLE hydrodynamic simulations. So long as star formation-driven outflows are present, the transition mass scale is almost independent of subgrid parameter choice. (ProQuest: ... denotes formulae/symbols omitted.)
We use the hydrodynamical EAGLE simulation to study the magnitude and origin of the scatter in the stellar mass-halo mass relation for central galaxies. We separate cause and effect by correlating ...stellar masses in the baryonic simulation with halo properties in a matched dark matter only (DMO) simulation. The scatter in stellar mass increases with redshift and decreases with halo mass. At z = 0.1, it declines from 0.25 dex at M..., DMO ... 10... M... to 0.12 dex at M200, DMO ... 10... M..., but the trend is weak above 1012 M... For M..., DMO < 10... M... up to 0.04 dex of the scatter is due to scatter in the halo concentration. At fixed halo mass, a larger stellar mass corresponds to a more concentrated halo. This is likely because higher concentrations imply earlier formation times and hence more time for accretion and star formation, and/or because feedback is less efficient in haloes with higher binding energies. The maximum circular velocity, Vmax, DMO, and binding energy are therefore more fundamental properties than halo mass, meaning that they are more accurate predictors of stellar mass, and we provide fitting formulae for their relations with stellar mass. However, concentration alone cannot explain the total scatter in the M...--M... relation, and it does not explain the scatter in Mstar-Vmax, DMO. Halo spin, sphericity, triaxiality, substructure and environment are also not responsible for the remaining scatter, which thus could be due to more complex halo properties or non-linear/stochastic baryonic effects. (ProQuest: ... denotes formulae/symbols omitted.)
Galactic outflow rates in the EAGLE simulations Mitchell, Peter D; Schaye, Joop; Bower, Richard G ...
Monthly notices of the Royal Astronomical Society,
2020, Letnik:
494, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We present measurements of galactic outflow rates from the eagle suite of cosmological simulations. We find that gas is removed from the interstellar medium (ISM) of central galaxies with a ...dimensionless mass loading factor that scales approximately with circular velocity as $V_{\mathrm{c}}^{-3/2}$ in the low-mass regime where stellar feedback dominates. Feedback from active galactic nuclei causes an upturn in the mass loading for halo masses ${\gt}10^{12} \, \mathrm{M_\odot }$. We find that more gas outflows through the halo virial radius than is removed from the ISM of galaxies, particularly at low redshifts, implying substantial mass loading within the circumgalactic medium. Outflow velocities span a wide range at a given halo mass/redshift, and on average increase positively with redshift and halo mass up to $M_{200} \sim 10^{12} \, \mathrm{M_\odot }$. Outflows exhibit a bimodal flow pattern on circumgalactic scales, aligned with the galactic minor axis. We present a number of like-for-like comparisons to outflow rates from other recent cosmological hydrodynamical simulations, and show that comparing the propagation of galactic winds as a function of radius reveals substantial discrepancies between different models. Relative to some other simulations, eagle favours a scenario for stellar feedback where agreement with the galaxy stellar mass function is achieved by removing smaller amounts of gas from the ISM, but with galactic winds that then propagate and entrain ambient gas out to larger radii.
The rapid growth phase of supermassive black holes McAlpine, Stuart; Bower, Richard G; Rosario, David J ...
Monthly notices of the Royal Astronomical Society,
12/2018, Letnik:
481, Številka:
3
Journal Article
ABSTRACT
We present a comparison of galaxy atomic and molecular gas properties in three recent cosmological hydrodynamic simulations, namely SIMBA, EAGLE, and IllustrisTNG, versus observations from z ...∼ 0 to 2. These simulations all rely on similar subresolution prescriptions to model cold interstellar gas that they cannot represent directly, and qualitatively reproduce the observed z ≈ 0 H i and H2 mass functions (HIMFs and H2MFs, respectively), CO(1–0) luminosity functions (COLFs), and gas scaling relations versus stellar mass, specific star formation rate, and stellar surface density μ*, with some quantitative differences. To compare to the COLF, we apply an H2-to-CO conversion factor to the simulated galaxies based on their average molecular surface density and metallicity, yielding substantial variations in αCO and significant differences between models. Using this, predicted z = 0 COLFs agree better with data than predicted H2MFs. Out to z ∼ 2, EAGLE’s and SIMBA’s HIMFs and COLFs strongly increase, while IllustrisTNG’s HIMF declines and COLF evolves slowly. EAGLE and simba reproduce high-LCO(1–0) galaxies at z ∼ 1–2 as observed, owing partly to a median αCO(z = 2) ∼ 1 versus αCO(z = 0) ∼ 3. Examining H i, H2, and CO scaling relations, their trends with M* are broadly reproduced in all models, but EAGLE yields too little H i in green valley galaxies, IllustrisTNG and SIMBA overproduce cold gas in massive galaxies, and SIMBA overproduces molecular gas in small systems. Using SIMBA variants that exclude individual active galactic nucleus (AGN) feedback modules, we find that SIMBA’s AGN jet feedback is primarily responsible by lowering cold gas contents from z ∼ 1 → 0 by suppressing cold gas in $M_*\gtrsim 10^{10}{\rm \,M}_\odot$ galaxies, while X-ray feedback suppresses the formation of high-μ* systems.
PDF
