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Stellar winds of massive (⁠|$\gtrsim 9\, \mathrm{M_\odot }$|⁠) and very massive (⁠|$\gtrsim 100\, \mathrm{M_\odot }$|⁠) stars may play an important role in the metal-enrichment during the formation of star clusters. With novel high-resolution hydrodynamical griffin -project simulations, we investigate the rapid recycling of stellar wind-material during the formation of massive star clusters up to |$M_\mathrm{cluster}\sim 2\times 10^5\, \mathrm{M_\odot }$| in a low-metallicity dwarf galaxy starburst. The simulation realizes new stars from a stellar initial mass function (IMF) between |$0.08$| and |$\sim 400\, \mathrm{M_\odot }$| and follows stellar winds, radiation and supernova-feedback of single massive stars with evolution tracks. Star clusters form on time-scales less than ∼5 Myr, and their supernova-material is very inefficiently recycled. Stellar wind-material, however, is trapped in massive clusters resulting in the formation of stars self-enriched in Na, Al, and N within only a few Myr. Wind-enriched (second population, 2P) stars can be centrally concentrated in the most massive clusters (⁠|$\gtrsim 10^4\, \mathrm{M_\odot }$|⁠) and the locked wind-material increases approximately as |$M_\mathrm{cluster}^{2}$|⁠. These trends resemble the characteristics of observed 2P stars in globular clusters (GCs). We fit scaling relations to the lognormal distributed wind-mass fractions and extrapolate to possible GC progenitors of |$M_\mathrm{cluster}=10^7\, \mathrm{M_\odot }$| to investigate whether a dominant 2P could form. This can only happen if the IMF is well-sampled, single massive stars produce at least a factor of a few more enriched winds, for example, through a top-heavy IMF, and a significant fraction of the first population (unenriched) stars is lost during cluster evolution. [ABSTRACT FROM AUTHOR]

In this study of the 'Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series, we focus on the hardening and coalescing process of supermassive black hole (SMBH) binaries in galaxy mergers. For simulations including different galaxy formation processes (i.e. gas cooling, star formation, SMBH accretion, stellar, and AGN feedback), we systematically control the effect of stochastic eccentricity by fixing it to similar values during the SMBH hardening phase. We find a strong correlation between the SMBH merger time-scales and the presence of nuclear star formation. Throughout the galaxy merging process, gas condenses at the centre due to cooling and tidal torques, leading to nuclear star formation. These recently formed stars, which inherit low angular momenta from the gas, contribute to the loss cone and assist in the SMBH hardening via three-body interactions. Compared to non-radiative hydrodynamical runs, the SMBH merger time-scales measured from the runs including cooling, stellar, and SMBH physical processes tend to be shortened by a factor of ∼1.7. After fixing the eccentricity to the range of e ∼ 0.6–0.8 during the hardening phase, the simulations with AGN feedback reveal merger time-scales of ∼100–500 Myr for disc mergers and ∼1–2 Gyr for elliptical mergers. With a semi-analytical approach, we find that the torque interaction between the binary and its circumbinary disc has minimal impact on the shrinking of the binary orbit in our retrograde galaxy merger. Our results are useful in improving the modelling of SMBH merger time-scales and gravitational-wave event rates. [ABSTRACT FROM AUTHOR]

We present new griffin project hydrodynamical simulations that model the formation of galactic star cluster populations in low-metallicity (Z = 0.00021) dwarf galaxies, including radiation, supernova, and stellar wind feedback of individual massive stars. In the simulations, stars are sampled from the stellar initial mass function (IMF) down to the hydrogen-burning limit of 0.08 M⊙. Mass conservation is enforced within a radius of 1 pc for the formation of massive stars. We find that massive stars are preferentially found in star clusters and follow a correlation set at birth between the highest initial stellar mass and the star cluster mass that differs from pure stochastic IMF sampling. With a fully sampled IMF, star clusters lose mass in the galactic tidal field according to mass-loss rates observed in nearby galaxies. Of the released stellar feedback, 60 per cent of the supernova material and up to 35 per cent of the wind material reside either in the hot interstellar medium (ISM) or in gaseous, metal-enriched outflows. While stellar winds (instantaneously) and supernovae (delayed) start enriching the ISM right after the first massive stars form, the formation of supernova-enriched stars and star clusters is significantly delayed (by >50 Myr) compared to the formation of stars and star clusters enriched by stellar winds. Overall, supernova ejecta dominate the enrichment by mass, while the number of enriched stars is determined by continuous stellar winds. These results present a concept for the formation of chemically distinct populations of stars in bound star clusters, reminiscent of multiple populations in globular clusters. [ABSTRACT FROM AUTHOR]

We present magnetohydrodynamic (MHD) simulations of the star-forming multiphase interstellar medium (ISM) in stratified galactic patches with gas surface densities Σgas = 10, 30, 50, and 100 |$\mathrm{M_\odot \, pc^{-2}}$|⁠. The silcc project simulation framework accounts for non-equilibrium thermal and chemical processes in the warm and cold ISM. The sink-based star formation and feedback model includes stellar winds, hydrogen-ionizing UV radiation, core-collapse supernovae, and cosmic ray (CR) injection and diffusion. The simulations follow the observed relation between Σgas and the star formation rate surface density ΣSFR. CRs qualitatively change the outflow phase structure. Without CRs, the outflows transition from a two-phase (warm and hot at 1 kpc) to a single-phase (hot at 2 kpc) structure. With CRs, the outflow always has three phases (cold, warm, and hot), dominated in mass by the warm phase. The impact of CRs on mass loading decreases for higher Σgas and the mass loading factors of the CR-supported outflows are of order unity independent of ΣSFR. Similar to observations, vertical velocity dispersions of the warm ionized medium (WIM) and the cold neutral medium (CNM) correlate with the star formation rate as |$\sigma _\mathrm{z} \propto \Sigma _\mathrm{SFR}^a$|⁠ , with a ∼ 0.20. In the absence of stellar feedback, we find no correlation. The velocity dispersion of the WIM is a factor ∼2.2 higher than that of the CNM, in agreement with local observations. For |$\Sigma _\mathrm{SFR} \gtrsim 1.5 \times 10^{-2}\, \mathrm{M}_\odot \, \mathrm{yr}^{-1}\, \mathrm{kpc}^{-2}$| the WIM motions become supersonic. [ABSTRACT FROM AUTHOR]

One of the primary goals when studying galaxy formation is to understand how the luminous component of the Universe, galaxies, relate to the growth of structure which is dominated by the gravitational collapse of dark matter haloes. The stellar-to-halo mass relation probes how galaxies occupy dark matter haloes and what that entails for their star formation history. We deliver the first self-consistent empirical model that can place constraints on the stellar-to-halo mass relation down to log stellar mass log10(m */M⊙) ≤ 5.0 by fitting our model directly to Local Group dwarf data. This is accomplished by penalizing galaxy growth in late-forming, low-mass haloes by mimicking the effects of reionization. This process serves to regulate the number density of galaxies by altering the scatter in halo peak mass |$M^{\mathrm{peak}}_{h}$| at fixed stellar mass, creating a tighter scatter than would otherwise exist without a high- z quenching mechanism. Our results indicate that the previously established double-power law stellar-to-halo mass relation can be extended to include galaxies with |$\log _{10}(M^{\mathrm{peak}}_{\mathrm{h}}/{\rm M}_{\odot })\gtrsim 10.0$|⁠. Furthermore, we show that haloes with |$\log _{10}(M^{\mathrm{peak}}_{\mathrm{h}}/{\rm M}_{\odot })\lesssim 9.3$| by z = 4 are unlikely to host a galaxy with log10(m */M⊙) > 5.0. [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 a photometric analysis of star and star cluster (SC) formation in a high-resolution simulation of a dwarf galaxy starburst that allows the formation of individual stars to be followed. Previous work demonstrated that the properties of the SCs formed in the simulation are in good agreement with observations. In this paper, we create mock spectral energy distributions and broad-band photometric images using the radiative transfer code skirt 9. We test several observational star formation rate (SFR) tracers and find that 24  |$\mu$| m, total infrared and Hα trace the underlying SFR during the (post)starburst phase, while UV tracers yield a more accurate picture of star formation during quiescent phases prior to and after the merger. We then place the simulated galaxy at distances of 10 and 50 Mpc and use aperture photometry at Hubble Space Telescope resolution to analyse the simulated SC population. During the starburst phase, a hierarchically forming set of SCs leads inaccurate source separation because of crowding. This results in estimated SC mass function slopes that are up to ∼0.3 shallower than the true slope of ∼−1.9 to −2 found for the bound clusters identified from the particle data in the simulation. The masses of the largest clusters are overestimated by a factor of up to 2.9 due to unresolved clusters within the apertures. The aperture-based analysis also produces a relation between cluster formation efficiency and SFR surface density that is slightly flatter than that recovered from bound clusters. The differences are strongest in quiescent SF environments. [ABSTRACT FROM AUTHOR]

Molecular outflows contributing to the matter cycle of star-forming galaxies are now observed in small and large systems at low and high redshift. Their physical origin is still unclear. In most theoretical studies, only warm ionized/neutral and hot gas outflowing from the interstellar medium is generated by star formation. We investigate an in situ H2 formation scenario in the outflow using high-resolution simulations, including non-equilibrium chemistry and self-gravity, of turbulent, warm, and atomic clouds with densities 0.1, 0.5, and |$1\, \mathrm{cm}^{-3}$| exposed to a magnetized hot wind. For cloud densities |$\gtrsim 0.5\, \mathrm{cm}^{-3}$|⁠ , a magnetized wind triggers H2 formation before cloud dispersal. Up to 3 per cent of the initial cloud mass can become molecular on |$\sim \! 10\, \mathrm{Myr}$| time-scales. The effect is stronger for winds with perpendicular B -fields and intermediate density clouds (⁠|$n_\mathrm{c}\sim 0.5\, \mathrm{cm}^{-3}$|⁠). Here, H2 formation can be boosted by up to one order of magnitude compared to isolated cooling clouds independent of self-gravity. Self-gravity preserves the densest clouds well past their |$\sim \! 15\, \mathrm{Myr}$| cloud crushing time-scales. This model could provide a plausible in situ origin for the observed molecular gas. All simulations form warm ionized gas, which represents an important observable phase. The amount of warm ionized gas is almost independent of the cloud density but solely depends on the magnetic field configuration in the wind. For low-density clouds (⁠|$0.1\, \mathrm{cm}^{-3}$|⁠), up to 60 per cent of the initially atomic cloud mass can become warm and ionized. [ABSTRACT FROM AUTHOR]

We present constraints on the emergence and evolution of passive galaxies with the empirical model emerge , which reproduces the evolution of stellar mass functions (SMFs), specific and cosmic star formation rates since |$z$|  ≈ 10, 'quenched' galaxy fractions, and correlation functions. At fixed halo mass, present-day passive galaxies are more massive than active galaxies, whereas at fixed stellar mass passive galaxies populate more massive haloes in agreement with observations. This effect naturally results from the shape and scatter of the stellar-to-halo mass relation. The stellar mass assembly of present-day passive galaxies is dominated by ' in situ ' star formation below ∼3 × 1011 M⊙ and by merging and accretion of ' ex situ ' formed stars at higher mass. The mass dependence is in tension with current cosmological simulations. Lower mass passive galaxies show extended star formation towards low redshift in agreement with IFU surveys. All passive galaxies have main progenitors on the 'main sequence of star formation' with the 'red sequence' appearing at |$z$|  ≈ 2. Above this redshift, over 95 per cent of the progenitors of passive galaxies are active. More than 90 per cent of |$z$|  ≈ 2 'main sequence' galaxies with m * > 1010 M⊙ evolve into present-day passive galaxies. Above redshift 6, more than 80 per cent of the observed SMFs above 109 M⊙ can be accounted for by progenitors of passive galaxies with m * > 1010 M⊙. This implies that high-redshift observations mainly probe the birth of present-day passive galaxies. emerge is available at github.com/bmoster/emerge. [ABSTRACT FROM AUTHOR]

We present a series of 10 × 2 cosmological zoom simulations of the formation of massive galaxies with and without a model for active galactic nucleus (AGN) feedback. Differences in stellar population and kinematic properties are evaluated by constructing mock integral field unit maps. The impact of the AGN is weak at high redshift when all systems are mostly fast rotating and disc-like. After z ∼ 1 the AGN simulations result in lower mass, older, less metal rich, and slower rotating systems with less discy isophotes – in general agreement with observations. 2D kinematic maps of in situ and accreted stars show that these differences result from reduced in-situ star formation due to AGN feedback. A full analysis of stellar orbits indicates that galaxies simulated with AGN are typically more triaxial and have higher fractions of x-tubes and box orbits and lower fractions of z-tubes. This trend can also be explained by reduced late in-situ star formation. We introduce a global parameter, ξ3, to characterize the anticorrelation between the third-order kinematic moment h 3 and the line-of-sight velocity (V avg/σ), and compare to ATLAS3 D observations. The kinematic correlation parameter ξ3 might be a useful diagnostic for large integral field surveys as it is a kinematic indicator for intrinsic shape and orbital content. [ABSTRACT FROM AUTHOR]

We present high-resolution hydrodynamical simulations of isolated dwarf galaxies including self-gravity, non-equilibrium cooling and chemistry, interstellar radiation fields (ISRF) and shielding, star formation, and stellar feedback. This includes spatially and temporally varying photoelectric (PE) heating, photoionization, resolved supernova (SN) blast waves and metal enrichment. A new flexible method to sample the stellar initial mass function allows us to follow the contribution to the ISRF, the metal output and the SN delay times of individual massive stars. We find that SNe play the dominant role in regulating the global star formation rate, shaping the multiphase interstellar medium (ISM) and driving galactic outflows. Outflow rates (with mass-loading factors of a few) and hot gas fractions of the ISM increase with the number of SNe exploding in low-density environments where radiative energy losses are low. While PE heating alone can suppress star formation as efficiently as SNe alone can do, it is unable to drive outflows and reproduce the multiphase ISM that emerges naturally whenever SNe are included. We discuss the potential origins for the discrepancy between our results and another recent study that claimed that PE heating dominates over SNe. In the absence of SNe and photoionization (mechanisms to disperse dense clouds), the impact of PE heating is highly overestimated owing to the (unrealistic) proximity of dense gas to the radiation sources. This leads to a substantial boost of the infrared continuum emission from the UV-irradiated dust and a far-infrared line-to-continuum ratio too low compared to observations. [ABSTRACT FROM AUTHOR]

We present three-dimensional hydrodynamical simulations showing the effect of kinetic and radiative active galactic nuclei (AGN) feedback on a model galaxy representing a massive quiescent low-redshift early-type galaxy of M* = 8.41 × 1010M☉, harbouring an MBH = 4 × 108 M☉ black hole surrounded by a cooling gaseous halo. We show that, for a total baryon fraction of ~20 per cent of the cosmological value, feedback from the AGN can keep the galaxy quiescent for about 4.35 Gyr and with properties consistent with black hole mass and X-ray luminosity scaling relations. However, this can only be achieved if the AGN feedback model includes both kinetic and radiative feedback modes. The simulation with only kinetic feedback fails to keep the model galaxy fully quiescent, while one with only radiative feedback leads to excessive black hole growth. For higher baryon fractions (e.g. 50 per cent of the cosmological value), the X-ray luminosities exceed observed values by at least one order of magnitude, and rapid cooling results in a star-forming galaxy. The AGN plays a major role in keeping the circumgalactic gas at observed metallicities of Z/Z☉ ≳ 0.3 within the central ~30 kpc by venting nuclear gas enriched with metals from residual star formation activity. As indicated by previous cosmological simulations, our results are consistent with a model for which the black hole mass and the total baryon fraction are set at higher redshifts z > 1 and the AGN alone can keep the model galaxy on observed scaling relations. Models without AGN feedback violate both the quiescence criterion as well as circumgalactic medium metallicity constraints. [ABSTRACT FROM AUTHOR]

We present three-dimensional radiation-hydrodynamical simulations of the impact of stellar winds, photoelectric heating, photodissociating and photoionizing radiation, and supernovae on the chemical composition and star formation in a stratified disc model. This is followed by a sink-based model for star clusters with populations of individual massive stars. Stellar winds and ionizing radiation regulate the star formation rate at a factor of ~10 below the simulation with only supernova feedback due to their immediate impact on the ambient interstellar medium after star formation. Ionizing radiation (with winds and supernovae) significantly reduces the ambient densities for most supernova explosions to ρ < 10-25 g cm-3, compared to 10-23g cm-3 for the model with only winds and supernovae. Radiation from massive stars reduces the amount of molecular hydrogen and increases the neutral hydrogen mass and volume filling fraction. Only this model results in a molecular gas depletion time-scale of 2 Gyr and shows the best agreement with observations. In the radiative models, the Hα emission is dominated by radiative recombination as opposed to collisional excitation (the dominant emission in non-radiative models), which only contributes ~1-10 per cent to the total Hα emission. Individual massive stars (M ≥ 30M☉) with short lifetimes are responsible for significant fluctuations in the Hα luminosities. The corresponding inferred star formation rates can underestimate the true instantaneous star formation rate by a factor of ~10. [ABSTRACT FROM AUTHOR]

We study the connection of star formation to atomic (HI) and molecular hydrogen (H2) in isolated, low-metallicity dwarf galaxies with high-resolution (mgas = 4 M⊙, Nngb = 100) smoothed particle hydrodynamics simulations. The model includes self-gravity, non-equilibrium cooling, shielding from a uniform and constant interstellar radiation field, the chemistry of H2 formation, H2-independent star formation, supernova feedback and metal enrichment. We find that the H2 mass fraction is sensitive to the adopted dust-to-gas ratio and the strength of the interstellar radiation field, while the star formation rate is not. Star formation is regulated by stellar feedback, keeping the gas out of thermal equilibrium for densities n < 1 cm−3. Because of the long chemical time-scales, the H2 mass remains out of chemical equilibrium throughout the simulation. Star formation is well correlated with cold (T ≤ 100 K) gas, but this dense and cold gas - the reservoir for star formation - is dominated by HI, not H2. In addition, a significant fraction of H2 resides in a diffuse, warm phase, which is not star-forming. The interstellar medium is dominated by warm gas (100 K < T ≤ 3 × 104 K) both in mass and in volume. The scaleheight of the gaseous disc increases with radius while the cold gas is always confined to a thin layer in the mid-plane. The cold gas fraction is regulated by feedback at small radii and by the assumed radiation field at large radii. The decreasing cold gas fractions result in a rapid increase in depletion time (up to 100 Gyr) for total gas surface densities ΣHI+H2≲ 10 M⊙pc−2, in agreement with observations of dwarf galaxies in the Kennicutt-Schmidt plane. [ABSTRACT FROM AUTHOR]

We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of Mstel = 8.8 × 1010-6.0 × 1011 M☉. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 haloes with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter haloes and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed MBH-σ relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of 2 compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ~10-100 higher X-ray luminosities than observed. The mechanical/radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with σ = 200 km s-1, the X-ray luminosity is reduced from 1042 erg s-1 to 1040 erg s-1. It also efficiently suppresses late-time star formation, reducing the specific star formation rate from 10-10.5 yr-1 to 10-14 yr-1 on average and resulting in quiescent galaxies since z = 2, whereas the thermal feedback model shows higher late-time in situ star formation rates than observed. [ABSTRACT FROM AUTHOR]

We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, Rmaje), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ~ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions. [ABSTRACT FROM AUTHOR]

We present measurements of the star formation rate (SFR) in the early-type galaxies (ETGs) of the ATLAS3D sample, based on Wide-field Infrared Survey Explorer (WISE) 22 μm and Galaxy Evolution Explorer far-ultraviolet emission. We combine these with gas masses estimated from 12CO and H i data in order to investigate the star formation efficiency (SFE) in a larger sample of ETGs than previously available. We first recalibrate (based on WISE data) the relation between old stellar populations (traced at Ks band) and 22 μm luminosity, allowing us to remove the contribution of 22 μm emission from circumstellar dust. We then go on to investigate the position of ETGs on the Kennicutt–Schmidt (KS) relation. Molecular gas-rich ETGs have comparable star formation surface densities to normal spiral galaxy centres, but they lie systematically offset from the KS relation, having lower SFEs by a factor of ≈2.5 (in agreement with other authors). This effect is driven by galaxies where a substantial fraction of the molecular material is in the rising part of the rotation curve, and shear is high. We show here for the first time that although the number of stars formed per unit gas mass per unit time is lower in ETGs, it seems that the amount of stars formed per free-fall time is approximately constant. The scatter around this dynamical relation still correlates with galaxy properties such as the shape of the potential in the inner regions. This leads us to suggest that dynamical properties (such as shear or the global stability of the gas) may be important second parameters that regulate star formation and cause much of the scatter around star formation relations. [ABSTRACT FROM AUTHOR]

We study how feedback influences baryon infall on to galaxies using cosmological, zoom-in simulations of haloes with present mass Mvir = 6.9 × 1011 to 1.7 × 1012 M⊙. Starting at z = 4 from identical initial conditions, implementations of weak and strong stellar feedback produce bulge- and disc-dominated galaxies, respectively. Strong feedback favours disc formation: (1) because conversion of gas into stars is suppressed at early times, as required by abundance matching arguments, resulting in flat star formation histories and higher gas fractions; (2) because 50 per cent of the stars form in situ from recycled disc gas with angular momentum only weakly related to that of the z = 0 dark halo; (3) because late-time gas accretion is typically an order of magnitude stronger and has higher specific angular momentum, with recycled gas dominating over primordial infall; (4) because 25–30 per cent of the total accreted gas is ejected entirely before z ∼ 1, removing primarily low angular momentum material which enriches the nearby intergalactic medium. Most recycled gas roughly conserves its angular momentum, but material ejected for long times and to large radii can gain significant angular momentum before re-accretion. These processes lower galaxy formation efficiency in addition to promoting disc formation. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present a detailed comparison between numerical cosmological hydrodynamic zoom simulations and the semi-analytic model (SAM) of Somerville et al., run within merger trees extracted from the simulations. The high-resolution simulations represent 48 individual haloes with virial masses in the range . They include radiative H and He cooling, photoionization, star formation and thermal supernova (SN) feedback. We compare with different SAM versions including only this complement of physical processes, and also ones including SN-driven winds, metal cooling and feedback from active galactic nuclei (AGN). Our analysis is focused on the cosmic evolution of the baryon content in galaxies and its division into various components (stars, cold gas and hot gas), as well as how those galaxies acquired their gas and stellar mass. Both the SAMs and simulations are compared with observational relations between halo mass and stellar mass, and between stellar mass and star formation rate, at low and high redshifts. We find some points of agreement and some important disagreements. SAMs that include the same physical processes as the simulations reproduce the total baryon fraction in haloes and the fraction of cold gas plus stars in the central galaxy to better than 20 per cent. However, the simulations turn out to have much higher star formation efficiencies (by about a factor of 10) than the SAMs, despite nominally being both normalized to the same empirical Kennicutt relation at z= 0. Therefore the cold gas is consumed much more rapidly in the simulations, and stars form much earlier. Also, simulations show a transition from stellar mass growth that is dominated by in situ formation of stars to growth that is predominantly through accretion of stars formed in external galaxies. In SAMs, stellar growth is always dominated by in situ star formation, because they significantly underpredict the fraction of mass growth from accreted stars relative to the simulations. In addition, SAMs overpredict the overall gas accretion rates relative to the simulations, and overestimate the fraction of 'hot' relative to 'cold' accretion. We discuss the reasons for these discrepancies, and identify several physical processes that are missing in our SAM and in other SAMs but which should be included. We also highlight physical processes that are neglected in the simulations studied here, but which appear to be crucial in order to understand the properties of real 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]

BSTRACT [ABSTRACT FROM AUTHOR]

We have carried out a survey for CO J= 1-0 and J= 2-1 emission in the 260 early-type galaxies of the volume-limited ATLAS sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo cluster members. Sample members are dynamically hot galaxies with a median stellar mass ∼3 × 10 M; they are selected by their morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 ± 0.03, with no dependence on the K luminosity and only a modest dependence on the dynamical mass. There are a dozen CO detections among the Virgo cluster members; statistical analysis of their H mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H masses ≳10 M and these are in low-density environments. We do find a significant trend between the molecular content and stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying the molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various subclasses of early-type galaxies. [ABSTRACT FROM AUTHOR]

A simple model for the evolution of disc galaxies is presented. We adopt three numbers from observations of the Milky Way disc, the local surface mass density, the stellar scalelength (of the assumed exponential disc), , the amplitude of the (assumed flat) rotation curve, and physically, the (local) dynamical Kennicutt star formation prescription, standard chemical evolution equations assuming a Salpeter initial mass function and a model for spectral evolution of stellar populations. We can determine the detailed evolution of the model with only the addition of standard cosmological scalings with the time of the dimensional parameters. A surprising wealth of detailed specifications follows from this prescription including the gaseous infall rate as a function of radius and time, the distribution of stellar ages and metallicities with time and radius, surface brightness profiles at different wavelengths, colours, etc. Some of the detailed properties are as follows: the global gas infall rate and the global star formation rate are almost constant at 2–3 and during the evolution of the disc. The present-day total masses in stars and in gas are and , respectively, and the disc has an absolute K-band magnitude of −23.2. The present-day stellar scalelength (normalized to 3 kpc) in the K band and is larger than at shorter wavelengths. At the solar neighbourhood stars started to form ≈10 Gyr ago at an increasing rate, peaking four billion years ago and then slowly declining in good agreement with observations. The mean age of long-lived stars at the solar neighbourhood is about 4 Gyr. The local surface densities of the stars and gas are 35 and , respectively. The metallicity distribution of the stars at the solar radius is narrow with a peak at . The present-day metallicity gradient is −0.046 dex kpc−1 and has been significantly steeper in the past. Using a Chabrier initial mass function increases the luminosity of the model and results in a steeper metallicity gradient. The local metallicity distribution is only weakly affected. Different formulations for threshold densities for star formation have been tested and lead to a truncation of the stellar disc at about 12 kpc. Comparisons with the current and local fossil evidence provide support for the model, which can then be used to assess other local disc galaxies, the evolution of disc galaxies in deep optical surveys and also for theoretical investigations such as simulations of merging disc galaxies. [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]