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With its cored surface brightness profile, the elliptical galaxy NGC 5419 appears as a typical high-mass early-type galaxy (ETG). However, the galaxy hosts two distinct nuclei in its center. We use high-signal MUSE (Multi-unit Spectroscopic Explorer (Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 099.B-0193(A).)) spectral observations and novel triaxial dynamical orbit models to reveal a surprisingly isotropic central orbit distribution in NGC 5419. Recent collisionless simulations of merging massive ETGs suggest a two-phase core formation model, in which the low-density stellar core forms rapidly by supermassive black holes (SMBHs) sinking into the center due to dynamical friction. Only afterwards do the SMBHs form a hard binary, and the black hole scouring process slowly changes the central orbit distribution from isotropic to tangential. The observed cored density profile, the double nucleus, and the isotropic center of NGC 5419 together thus point to an intermediate evolutionary state where the first phase of core formation has taken place, yet the scouring process is only beginning. This implies that the double nucleus is an SMBH binary. Our triaxial dynamical models indicate a total mass of the two SMBHs in the center of NGC 5419 of M BH = (1.0 ± 0.08) × 1010 M ⊙. Moreover, we find that NGC 5419's complex kinematically distinct core can be explained by a coherent flip of the direction of orbital rotation of stars on tube orbits at ∼3 kpc distance from the galaxy center together with projection effects. This is also in agreement with merger simulations hosting SMBHs in the same mass regime. [ABSTRACT FROM AUTHOR]

The dividing line between galaxies that are quenched by reionization ("relics") and galaxies that survive reionization (i.e., continue forming stars) is commonly discussed in terms of a halo mass threshold. We probe this threshold in a physically more complete and accurate way than has been possible to date, using five extremely high resolution (M target = 4 M ⊙) cosmological zoom-in simulations of dwarf galaxies within the halo mass range (1–4) × 109 M ⊙. The employed LYRA simulation model features resolved interstellar medium physics and individual, resolved supernova explosions. Interestingly, two out of five of the simulated dwarf galaxies lie close to the threshold mass but are neither full reionization relics nor full reionization survivors. These galaxies initially quench at the time of reionization but merely remain quiescent for ∼500 Myr. At z ∼ 5 they recommence star formation in a synchronous way and remain star-forming until the present day. The parallel timing indicates consistent sound-crossing and cooling times between the halos. While the star formation histories we find are diverse, we show that they are directly related to the ability of a given halo to retain and cool gas. Whereas the latter is most strongly dependent on the mass (or virial temperature) of the host halo at the time of reionization, it also depends on its growth history, the UV background (and its decrease at late times), and the amount of metals retained within the halo. [ABSTRACT FROM AUTHOR]

We present [C ii ] synthetic observations of smoothed particle hydrodynamics (SPH) simulations of a dwarf galaxy merger. The merging process varies the star formation rate (SFR) by more than three orders of magnitude. Several star clusters are formed, the feedback of which disperses and unbinds the dense gas through expanding H ii regions and supernova (SN) explosions. For galaxies with properties similar to the modeled ones, we find that the [C ii ] emission remains optically thin throughout the merging process. We identify the warm neutral medium ( 3 < log T gas < 4 with χ HI > 2 χ H2) to be the primary source of [C ii ] emission (∼58% contribution), although at stages when the H ii regions are young and dense (during star cluster formation or SNe in the form of ionized bubbles), they can contribute ≳50% to the total [C ii ] emission. We find that the [C ii ]/far-IR (FIR) ratio decreases owing to thermal saturation of the [C ii ] emission caused by strong far-UV radiation fields emitted by the massive star clusters, leading to a [C ii ] deficit medium. We investigate the [C ii ]âˆ'SFR relation and find an approximately linear correlation that agrees well with observations, particularly those from the Dwarf Galaxy Survey. Our simulation reproduces the observed trends of [C ii ]/FIR versus ÎŁSFR and ÎŁFIR, and it agrees well with the Kennicutt relation of SFRâˆ'FIR luminosity. We propose that local peaks of [C ii ] in resolved observations may provide evidence for ongoing massive cluster formation. [ABSTRACT FROM AUTHOR]

Stellar metallicity distribution functions (MDFs) have been measured for resolved stellar populations in the outer halos of many galaxies in nearby groups. Among them, the MDF of NGC 5128, the central giant elliptical in the Centaurus group, provides essential constraints for theories of massive galaxy formation and hierarchical assembly. To investigate the formation and chemical evolution history of the outer halo of giant elliptical galaxies, we examine the chemical properties of three zoom-in high-resolution cosmological hydrodynamical simulations of an NGC 5128â€"like giant elliptical galaxy and compare their outer halo MDFs to the observed one of NGC 5128. Even though the simulated galaxies have different merging histories and age distributions, all predicted MDFs are in good qualitative agreement with the observed one. The median metallicity of the simulated galaxies is, on average, [M/H] = âˆ'0.41 ± 0.06 compared to the observed value of [M/H] = âˆ'0.38 ± 0.02 for NGC 5128, and the dispersion in metallicity is ∼0.77 dex for both observed and simulated galaxies. We investigate the origin of the stars ending up in the outer halo field of simulated galaxies and show that most have an “accreted” origin, formed in other small galaxies and later accreted in mergers. Only ∼15% of the stars are formed in situ within the main progenitor of the galaxy and radially migrate outward. We show that the contribution of metal-rich in situ stars is subdominant in the outer halos of our simulated galaxies but can be prominent in the inner regions. [ABSTRACT FROM AUTHOR]

We analyze the three-dimensional shapes and kinematics of the young star cluster population forming in a high-resolution griffin project simulation of a metal-poor dwarf galaxy starburst. The star clusters, which follow a power-law mass distribution, form from the cold phase interstellar medium with an initial mass function sampled with individual stars down to four solar masses at sub-parsec spatial resolution. Massive stars and their important feedback mechanisms are modeled in detail. The simulated clusters follow a surprisingly tight relation between the specific angular momentum and mass with indications of two sub-populations. Massive clusters (Mcl ≳ 3 × 104M⊙) have the highest specific angular momenta at low ellipticities (ϵ ∼ 0.2) and show alignment between their shapes and rotation. Lower mass clusters have lower specific angular momenta with larger scatter, show a broader range of elongations, and are typically misaligned indicating that they are not shaped by rotation. The most massive clusters (M ≳ 105M⊙) accrete gas and protoclusters from a ≲100 pc scale local galactic environment on a t ≲ 10 Myr timescale, inheriting the ambient angular momentum properties. Their two-dimensional kinematic maps show ordered rotation at formation, up to v ∼ 8.5 km s−1, consistent with observed young massive clusters and old globular clusters, which they might evolve into. The massive clusters have angular momentum parameters λR ≲ 0.5 and show Gauss–Hermite coefficients h3 that are anti-correlated with the velocity, indicating asymmetric line-of-sight velocity distributions as a signature of a dissipative formation process. [ABSTRACT FROM AUTHOR]

Metals in the hot gaseous halos of galaxies encode the history of star formation as well as the feedback processes that eject metals from the galaxies. X-ray observations suggest that massive galaxies have extended distributions of metals in their gas halos. We present predictions for the metal properties of massive galaxies and their gaseous halos from recent high-resolution zoom-in simulations that include mechanical and radiation-driven feedback from active galactic nuclei (AGN). In these simulations, AGN launch high-velocity outflows, mimicking observed broad absorption line winds. By comparing two sets of simulations with and without AGN feedback, we show that our prescription for AGN feedback is capable of driving winds and enriching halo gas "inside-out" by spreading centrally enriched metals to the outskirts of galaxies, into the halo and beyond. The metal (iron) profiles of halos simulated with AGN feedback have a flatter slope than those without AGN feedback, consistent with recent X-ray observations. The predicted gas iron abundance of group scale galaxies simulated with AGN feedback is ZFe = 0.23 ZFe,⊙ at 0.5r500, which is 2.5 times higher than that in simulations without AGN feedback. In these simulations, AGN winds are also important for the metal enrichment of the intergalactic medium, as the vast majority of metals ejected from the galaxy by AGN-driven winds end up beyond the halo virial radius. [ABSTRACT FROM AUTHOR]

We analyze the spectra, spatial distributions, and kinematics of Hα, [NII], and [S II] emission in a sample of 38, z ~ 2.2 UV/optically selected star-forming galaxies (SFGs) from the SINS and zC-SINF surveys, 34 of which were observed in the adaptive optics mode of SINFONI and 30 of those contain data presented for the first time here. This is supplemented by kinematic data from 43 z ~ 1-2.5 galaxies from the literature. None of these 81 galaxies is an obvious major merger. We find that the kinematic classification of high-z SFGs as "dispersion dominated" or rotation dominated" correlates most strongly with their intrinsic sizes. Smaller galaxies are more likely "dispersion-dominated" for two main reasons: (1) the rotation velocity scales linearly with galaxy size but intrinsic velocity dispersion does not depend on size or may even increase in smaller galaxies, and as such, their ratio is systematically lower for smaller galaxies, and (2) beam smearing strongly decreases large-scale velocity gradients and increases observed dispersion much more for galaxies with sizes at or below the resolution. Dispersion-dominated SFGs may thus have intrinsic properties similar to "rotation-dominated" SFGs, but are primarily more compact, lower mass, less metal enriched, and may have higher gas fractions, plausibly because they represent an earlier evolutionary state. [ABSTRACT FROM AUTHOR]

Dynamical modeling and strong-lensing data indicate that the total density profiles of early-type galaxies are close to isothermal, i.e., ρtot ≈ rγ with γ ≈ -2. To understand the origin of this universal slope we study a set of simulated spheroids formed in isolated binary mergers as well as the formation within the cosmological framework. The total stellar plus darkmatter density profiles can always be described by a power law with an index of γ ≈ -2.1 with a tendency toward steeper slopes for more compact, lower-mass ellipticals. In the binary mergers the amount of gas involved in the merger determines the precise steepness of the slope. This agrees with results from the cosmological simulations where ellipticals with steeper slopes have a higher fraction of stars formed in situ. Each gas-poor merger event evolves the slope toward γ ∼ -2, once this slope is reached further merger events do not change it anymore. All our ellipticals have flat intrinsic combined stellar and dark matter velocity dispersion profiles. We conclude that flat velocity dispersion profiles and total density distributions with a slope of γ ∼ -2 for the combined system of stars and dark matter act as a natural attractor. The variety of complex formation histories as present in cosmological simulations, including major as well as minor merger events, is essential to generate the full range of observed density slopes seen for present-day elliptical galaxies. [ABSTRACT FROM AUTHOR]

Many observed massive star-forming ʑ ≈ 2 galaxies are large disks that exhibit irregular morphologies, with ≈1 kpc, ≈108-1010 Mʘ clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M∗ ≈ 1010.5 Mʘ galaxies in ≈1012 Mʘ halos at ʑ ≈ 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (fg ≈ 50%), and high specific star formation rates (≳1 Gyr-1). In accord with recent models, giant clumps (Mclump ≈ (5 x 108-109) Mʘ) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce, well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration. [ABSTRACT FROM AUTHOR]

We analyze 40 cosmological re-simulations of individual massive galaxies with present-day stellar masses of M* > 6.3 x 1010 M⊙ in order to investigate the physical origin of the observed strong increase in galaxy sizes and the decrease of the stellar velocity dispersions since redshift z ≈ 2. At present 25 out of 40 galaxies are quiescent with structural parameters (sizes and velocity dispersions) in agreement with local early-type galaxies. At z = 2 all simulated galaxies with M* ≳ 1011 M⊙ (11 out of 40) at z = 2 are compact with projected half-mass radii of ≈0.77 (±0,24) kpc and line-of-sight velocity dispersions within the projected half-mass radius of ≈262 (±28) km s-1 (3 out of 11 are already quiescent). Similar to observed compact early-type galaxies at high redshift, the simulated galaxies are clearly offset from the local mass-size and mass-velocity dispersion relations. Toward redshift zero the sizes increase by a factor of ~5-6, following R1/2 ∝ (1 + Z)α with α = -1.44 for quiescent galaxies (α = - 1.12 for all galaxies). The velocity dispersions drop by about one-third since z ≈ 2, following at σ1/2 ∝ (1 + z)β with β = 0.44 for the quiescent galaxies (β = 0.37 for all galaxies). The simulated size and dispersion evolution is in good agreement with observations and results from the subsequent accretion and merging of stellar systems at z ≲ 2, which is a natural consequence of the hierarchical structure formation. A significant number of the simulated massive galaxies (7 out of 40) experience no merger more massive than 1:4 (usually considered as major mergers). On average, the dominant accretion mode is stellar minor mergers with a mass-weighted mass ratio of 1:5. We therefore conclude that the evolution of massive early-type galaxies since z ≈ 2 and their present-day properties are predominantly determined by frequent "minor" mergers of moderate mass ratios and not by major mergers alone. [ABSTRACT FROM AUTHOR]

Hydrodynamic simulations of galaxies with active galactic nuclei (AGNs) have typically employed feedback that is purely local, i.e., an injection of energy to the immediate neighborhood of the black hole (BH). We perform GADGET-2 simulations of massive elliptical galaxies with an additional feedback component: an observationally calibrated X-ray radiation field which emanates from the BH and heats gas out to large radii from the galaxy center. We find that including the heating and radiation pressure associated with this X-ray flux in our simulations enhances the effects which are commonly reported from AGN feedback. This new feedback model is twice as effective as traditional feedback at suppressing star formation, produces three times less star formation in the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also significantly more effective than an X-ray background in reducing the number of satellite galaxies. [ABSTRACT FROM AUTHOR]

We re-examine the age distribution of star clusters in the Antennae in the context of N-body+hydrodynamical simulations of these interacting galaxies. All of the simulations that account for the observed morphology and other properties of the Antennae have star formation rates that vary relatively slowly with time, by factors of only 1.3-2.5 in the past 108 yr. In contrast, the observed age distribution of the clusters declines approximately as a power law, dN/dτ ∝ τγ with γ = -1.0, for ages 106 yr ≲ τ ≲ 109 yr. These two facts can only be reconciled if the clusters are disrupted progressively for at least ~108 yr and possibly ~109 yr. When we combine the simulated formation rates with a power-law model, ƒsurv ∝ τ δ, for the fraction of clusters that survive to each age r, we match the observed age distribution with exponents in the range -0.9 ≲ δ ≲ -0.6 (with a slightly different ö for each simulation). The similarity between δ and γ indicates that dN/dτ is shaped mainly by the disruption of clusters rather than variations in their formation rate. Thus, the situation in the interacting Antennae resembles that in relatively quiescent galaxies such as the Milky Way and the Magellanic Clouds. [ABSTRACT FROM AUTHOR]

Using SINFONI Hα, [N II], and [S II] AO data of 27 z ∼ 2 star-forming galaxies (SFGs) from the SINS and zC-SINF surveys, we explore the dependence of outflow strength (via the broad flux fraction) on various galaxy parameters. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius (∼a few kpc). Decomposition of the [S II] doublet into broad and narrow components suggests that this outflowing gas probably has a density of ∼10-100 cm–3, less than that of the star-forming gas (600 cm–3). There is a strong correlation of the Hα broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 M☼ yr–1 kpc–2. Above this threshold, we find that SFGs with log m* > 10 have similar or perhaps greater wind mass-loading factors (η = /SFR) and faster outflow velocities than lower mass SFGs, suggesting that the majority of outflowing gas at z ∼ 2 may derive from high-mass SFGs. The mass-loading factor is also correlated with the star formation rate (SFR), galaxy size, and inclination, such that smaller, more star-forming, and face-on galaxies launch more powerful outflows. We propose that the observed threshold for strong outflows and the observed mass loading of these winds can be explained by a simple model wherein break-out of winds is governed by pressure balance in the disk. [ABSTRACT FROM AUTHOR]

We present a sample of nine high-resolution cosmological simulations in the mass range of Mvir = 7 × 1011-4 × 1012M☼ starting from ΛCDM initial conditions. Our simulations include primordial radiative cooling, photoionization, star formation, supernova II feedback, but exclude supernova-driven winds and active galactic nucleus feedback. The simulated galaxies assemble in two phases, with the initial growth dominated by compact (r < reff) in situ star formation fueled by cold, low-entropy gas streams resulting in a very similar mean assembly redshift of zf, ins ∼ 2.5 for the in situ stellar component in all galaxies. The late growth is dominated by accretion of old stars formed in subunits outside the main galaxy (r > reff) resulting in an assembly redshift of zf, acc ∼ 0.5-1.5 with much larger scatter. We find a positive correlation between the fraction of accreted stars and the final mass of our galaxies. We show that gravitational feedback strongly suppresses late star formation in massive galaxies contributing to the observed galaxy color bimodality. The accretion of stellar material is also responsible for the observed size growth of early-type galaxies. In addition, we find that the dark matter fractions within the stellar half-mass radii continuously increase toward lower redshift from about fDM ∼ 0.05 at z ∼ 3 to fDM ∼ 0.1-0.3 at z = 0. Furthermore, the logarithmic slope of the total density profile is nearly isothermal at the present day (γ′ ∼ 1.9-2.2). Finally, the input of gravitational heating lowers the central dark matter densities in the galaxies, with the effect being smaller compared to simulations without supernova feedback. [ABSTRACT FROM AUTHOR]

We study the growth of black holes (BHs) in galaxies using three-dimensional smoothed particle hydrodynamic simulations with new implementations of the momentum mechanical feedback, and restriction of accreted elements to those that are gravitationally bound to the BH. We also include the feedback from the X-ray radiation emitted by the BH, which heats the surrounding gas in the host galaxies, and adds radial momentum to the fluid. We perform simulations of isolated galaxies and merging galaxies and test various feedback models with the new treatment of the Bondi radius criterion. We find that overall the BH growth is similar to what has been obtained by earlier works using the Springel, Di Matteo, & Hernquist algorithms. However, the outflowing wind velocities and mechanical energy emitted by winds are considerably higher (vw ∼ 1000-3000 km s–1) compared to the standard thermal feedback model (vw ∼ 50-100 km s–1). While the thermal feedback model emits only 0.1% of BH released energy in winds, the momentum feedback model emits more than 30% of the total energy released by the BH in winds. In the momentum feedback model, the degree of fluctuation in both radiant and wind output is considerably larger than in standard treatments. We check that the new model of BH mass accretion agrees with analytic results for the standard Bondi problem. [ABSTRACT FROM AUTHOR]