Simulations Of Galaxy Evolution Research Articles

Quasar Sightline and Galaxy Evolution (QSAGE) – III. The mass–metallicity and fundamental metallicity relation of z ≈ 2.2 galaxies

ABSTRACT We present analysis of the mass–metallicity relation (MZR) for a sample of 67 [O iii]-selected star-forming (SF) galaxies at a redshift range of z = 1.99−2.32 (zmed = 2.16) using Hubble Space Telescope Wide Field Camera 3 grism spectroscopy from the Quasar Sightline and Galaxy Evolution survey. Metallicities were determined using empirical gas-phase metallicity calibrations based on the strong emission lines [O ii]3727, 3729, [O iii]4959, 5007 and Hβ. SF galaxies were identified, and distinguished from active-galactic nuclei, via Mass–Excitation diagrams. Using z ∼ 0 metallicity calibrations, we observe a negative offset in the z = 2.2 MZR of ≈−0.51 dex in metallicity when compared to locally derived relationships, in agreement with previous literature analysis. A similar offset of ≈−0.46 dex in metallicity is found when using empirical metallicity calibrations that are suitable out to z ∼ 5, though our z = 2.2 MZR, in this case, has a shallower slope. We find agreement between our MZR and those predicted from various galaxy evolution models and simulations. Additionally, we explore the extended fundamental metallicity relation (FMR) which includes an additional dependence on star formation rate. Our results consistently support the existence of the FMR, as well as revealing an offset of 0.28 ± 0.04 dex in metallicity compared to locally derived relationships, consistent with previous studies at similar redshifts. We interpret the negative correlation with SFR at fixed mass, inferred from an FMR existing for our sample, as being caused by the efficient accretion of metal-poor gas fuelling SFR at cosmic noon.

Red riding on hood: exploring how galaxy colour depends on environment

ABSTRACT Galaxy populations are known to exhibit a strong colour bimodality, corresponding to blue star-forming and red quiescent subpopulations. The relative abundance of the two populations has been found to vary with stellar mass and environment. In this paper, we explore the effect of environment considering different types of measurements. We choose a sample of 49 911 galaxies with 0.05 < z < 0.18 from the Galaxy And Mass Assembly survey. We study the dependence of the fraction of red galaxies on different measures of the local environment as well as the large-scale `geometric’ environment defined by density gradients in the surrounding cosmic web. We find that the red galaxy fraction varies with the environment at fixed stellar mass. The red fraction depends more strongly on local environmental measures than on large-scale geometric environment measures. By comparing the different environmental densities, we show that no density measurement fully explains the observed environmental red fraction variation, suggesting the different measures of environmental density contain different information. We test whether the local environmental measures, when combined together, can explain all the observed environmental red fraction variation. The geometric environment has a small residual effect, and this effect is larger for voids than any other type of geometric environment. This could provide a test of the physics applied to cosmological-scale galaxy evolution simulations as it combines large-scale effects with local environmental impact.

Low-power jet–interstellar medium interaction in NGC 7319 revealed by JWST/MIRI MRS

We present JWST/MIRI MRS spectroscopy of NGC 7319, the largest galaxy in the Stephan’s Quintet, observed as part of the Early Release Observations (ERO). NGC 7319 hosts a type 2 active galactic nucleus (AGN) and a low-power radio jet (L1.4 GHz = 3.3 × 1022 W Hz−1) with two asymmetric radio hotspots at 430 pc (N2) and 1.5 kpc (S2) projected distances from the unresolved radio core. The MRS data suggest that the molecular material in the disk of the galaxy decelerates the jet and causes this length asymmetry. We find enhanced emission from warm and hot H2 (Tw = 330 ± 40 K, Th = 900 ± 60 K) and ionized gas at the intersection between the jet axis and dust lanes in the disk. This emission is coincident with the radio hotspot N2, the hotspot closer to the core, suggesting that the jet–interstellar medium (ISM) interaction decelerates the jet. Conversely, the mid-infrared emission at the more distant hotspot is fainter, more highly ionized, and with lower H2 excitation, suggesting a more diffuse atomic environment where the jet can progress to farther distances. At the N2 radio hotspot, the ionized gas mass (Mion = (2.4–12)×105 M⊙) is comparable to that of the warm H2, but the former is more turbulent (σion ∼ 300 vs. σH2 ∼ 150 km s−1), so the mechanical energy of the ionized gas is ∼1.3–10 times higher. From these estimates, we find that only < 1% of the jet energy remains as mechanical energy in these two ISM phases at N2. We also find extended (r > 0.3–1.5 kpc) high-ionization emission ([Mg V], [Ne VI], and [Ne V]) close to the radio hotspots. This initial analysis of NGC 7319 shows the potential of MIRI/MRS to investigate the AGN feedback mechanisms due to radio jets and their radiation field in the, often heavily dust-enshrouded, central regions of galaxies. Understanding these mechanisms is an essential ingredient in the development of cosmological simulations of galaxy evolution.

Empirically motivated early feedback: momentum input by stellar feedback in galaxy simulations inferred through observations

ABSTRACT We present a novel method for including the effects of early (pre-supernova) feedback in simulations of galaxy evolution. Rather than building a model which attempts to match idealized, small-scale simulations or analytic approximations, we rely on direct observational measurements of the time-scales over which star-forming molecular clouds are disrupted by early feedback. We combine observations of the spatial de-correlation between molecular gas and star formation tracers on ∼100 pc scales with an analytic framework for the expansion of feedback fronts driven by arbitrary sources or mechanisms, and use these to constrain the time-scale and momentum injection rate by early feedback. This allows us to directly inform our model for feedback from these observations, sidestepping the complexity of multiple feedback mechanisms and their interaction below the resolution scale. We demonstrate that this new model has significant effects on the spatial clustering of star formation, the structure of the ISM, and the driving of outflows from the galactic plane, while preserving the overall regulation of the galaxy-integrated star formation rate. We find that this new feedback model results in galaxies that regulate star formation through the rapid disruption of star-forming clouds, rather than by highly efficient, global galactic outflows. We also demonstrate that these results are robust to stochasticity, degraded numerical resolution, changes in the star formation model parameters, and variations in the single free model parameter that is unconstrained by observations.

MIGHTEE-H i: the H i size–mass relation over the last billion years

ABSTRACT We present the observed H i size–mass relation of 204 galaxies from the MIGHTEE Survey Early Science data. The high sensitivity of MeerKAT allows us to detect galaxies spanning more than 4 orders of magnitude in H i mass, ranging from dwarf galaxies to massive spirals, and including all morphological types. This is the first time the relation has been explored on a blind homogeneous data set that extends over a previously unexplored redshift range of 0 < z < 0.084, i.e. a period of around one billion years in cosmic time. The sample follows the same tight logarithmic relation derived from previous work, between the diameter ($D_{\rm H\, \small {\rm I}}$) and the mass ($M_{\rm H\, \small {\rm I}}$) of H i discs. We measure a slope of 0.501 ± 0.008, an intercept of $-3.252^{+0.073}_{-0.074}$, and an observed scatter of 0.057 dex. For the first time, we quantify the intrinsic scatter of 0.054 ± 0.003 dex (${\sim } 10 {{\ \rm per\ cent}}$), which provides a constraint for cosmological simulations of galaxy formation and evolution. We derive the relation as a function of galaxy type and find that their intrinsic scatters and slopes are consistent within the errors. We also calculate the $D_{\rm H\, \small {\rm I}}{ \!-\! }M_{\rm H\, \small {\rm I}}$ relation for two redshift bins and do not find any evidence for evolution with redshift. These results suggest that over a period of one billion years in look-back time, galaxy discs have not undergone significant evolution in their gas distribution and mean surface mass density, indicating a lack of dependence on both morphological type and redshift.

Uncertainties in supernova input rates drive qualitative differences in simulations of galaxy evolution

ABSTRACT Feedback from core collapse supernovae (SNe), the final stage of evolution of massive stars, is a key element in galaxy formation theory. The energy budget of SN feedback, as well as the duration over which SNe occur, are constrained by stellar lifetime models and the minimum mass star that ends its life as a SN. Simplifying approximations for this SN rate are ubiquitous in simulation studies. We show here how the choice of SN budget and timings (t0 for the delay between star formation and the first SN, τSN for the duration of SN injection, and the minimum SN progenitor mass) drive changes in the regulation of star formation and outflow launching. Extremely long delays for instantaneous injection of SN energy (t0 ≫ 20 Myr) reduces star formation and drive stronger outflows compared smaller delays. This effect is primarily driven by enhanced clustering of young stars. With continuous injection of energy, longer SN durations results in a larger fraction of SN energy deposited in low ambient gas densities, where cooling losses are lower. This is effect is particularly when driven by the choice of the minimum SN progenitor mass, which also sets the total SN energy budget. These underlying uncertainties mean that despite advances in the sub-grid modeling of SN feedback, serious difficulties in constraining the strength of SN feedback remain. We recommend future simulations use realistic SN injection durations, and bound their results using SN energy budgets and durations for minimum SN progenitors of 7 and 9 M⊙.

Evidence for A Hot Wind from High-resolution X-Ray Spectroscopic Observation of the Low-luminosity Active Galactic Nucleus in NGC 7213

Abstract Supermassive black holes (SMBHs) spend most of their lifetime accreting at a rate well below the Eddington limit, manifesting themselves as low-luminosity active galactic nuclei (LLAGNs). The prevalence of a hot wind from LLAGNs is a generic prediction by theories and numerical simulations of black hole accretion and has recently become a crucial ingredient of AGN kinetic feedback in cosmological simulations of galaxy evolution. However, direct observational evidence for this hot wind is still scarce. In this work, we identify significant Fe xxvi Lyα and Fe xxv Kα emission lines from high-resolution Chandra grating spectra of the LLAGN in NGC 7213, a nearby Sa galaxy hosting a ∼108 M ⊙ SMBH, confirming previous work. We find that these lines exhibit a blueshifted line-of-sight velocity of ∼1100 km s−1 and a high XXVI Lyα to XXV Kα flux ratio, implying for a ∼16 keV hot plasma. By confronting these spectral features with synthetic X-ray spectra based on our custom magnetohydrodynamical simulations, we find that the high-velocity, hot plasma can be naturally explained by the putative hot wind driven by the hot accretion flow powering this LLAGN. Alternative plausible origins of this hot plasma, including stellar activities, AGN photoionization, and the hot accretion flow itself, are quantitatively disfavored. The inferred kinetic energy and momentum carried by the wind can serve as strong feedback to the environment. We compare NGC 7213 to M81*, in which strong evidence for a hot wind was recently presented, and discuss implications on the universality and detectability of hot winds from LLAGNs.

Pre-supernova feedback mechanisms drive the destruction of molecular clouds in nearby star-forming disc galaxies

ABSTRACT It is a major open question which physical processes stop gas accretion on to giant molecular clouds (GMCs) and limit the efficiency at which gas is converted into stars. While feedback from supernova explosions has been the popular feedback mechanism included in simulations of galaxy formation and evolution, ‘early’ feedback mechanisms such as stellar winds, photoionization, and radiation pressure are expected to play an important role in dispersing the gas after the onset of star formation. These feedback processes typically take place on small scales (∼10–100 pc) and their effects have therefore been difficult to constrain in environments other than the Milky Way. We apply a novel statistical method to ∼1 arcsec resolution maps of CO and H α across a sample of nine nearby galaxies, to measure the time over which GMCs are dispersed by feedback from young, high-mass stars, as a function of the galactic environment. We find that GMCs are typically dispersed within ∼3 Myr on average after the emergence of unembedded high-mass stars, with variations within galaxies associated with morphological features rather than radial trends. Comparison with analytical predictions demonstrates that, independently of the environment, early feedback mechanisms (particularly photoionization and stellar winds) play a crucial role in dispersing GMCs and limiting their star formation efficiency in nearby galaxies. Finally, we show that the efficiency at which the energy injected by these early feedback mechanisms couples with the parent GMC is relatively low (a few tens of per cent), such that the vast majority of momentum and energy emitted by the young stellar populations escapes the parent GMC.

Magnetic fields in elliptical galaxies: using the Laing–Garrington effect in radio galaxies and polarized emission from background radio sources

ABSTRACT Magnetic fields in elliptical galaxies are poorly constrained because of a lack of significant synchrotron emission from them. In this paper, we explore the properties of magnetic fields in ellipticals using two methods. First, we exploit the Laing–Garrington effect (asymmetry in the observed polarization fraction between radio galaxy jets) for 57 galaxies with redshifts up to 0.5. We use the differences in polarization fraction and rotation measure between the jet and counterjet to estimate the small- and large-scale magnetic fields in and around ellipticals (including their circumgalactic medium). We find that the small-scale field (at scales smaller than the driving scale of turbulence, approximately 300 pc) lies in the range 0.1–2.75 $\mu{\rm G}$. The large-scale field (at scales of 100 kpc) is an order of magnitude smaller than the small-scale field. In the second method, we cross-match the Faraday rotation measures (RMs) of a few hundred (out of 3098) extragalactic radio sources with galaxy catalogues to explore the effect of the number and morphology of intervening galaxies on the observed RM distribution. We use both Gaussian and non-Gaussian functions to describe the RM distribution and to derive its statistical properties. Finally, using the difference in the observed polarization fraction between the intervening spirals and ellipticals, we estimate the small-scale magnetic fields at the centre of ellipticals to be ∼6 $\mu{\rm G}$. Both methods with different observations and analysis techniques give magnetic field strengths consistent with previous studies (≤10 $\mu{\rm G}$). The results can be used to constrain dynamo theories and galaxy evolution simulations.

Cosmic metal density evolution in neutral gas: insights from observations and cosmological simulations

ABSTRACT We contrast the latest observations of the cosmic metal density in neutral gas ($\rho _{ {met,neu}}$) with three cosmological galaxy evolution simulations: L-Galaxies 2020, TNG100, and EAGLE. We find that the fraction of total metals that are in neutral gas is <40 per cent at 3 ≲ $z$ ≲ 5 in these simulations, whereas observations of damped Lyman-α (DLA) systems suggest ≳ 85 per cent. In all three simulations, hot, low-density gas is also a major contributor to the cosmic metal budget, even at high redshift. By considering the evolution in cosmic SFR density ($\rho _{ {\rm {\small {sfr}}}}$), neutral gas density ($\rho _{ {HI}}$), and mean gas-phase metallicity ($[\langle {} {M/H}\rangle ]_{ {neu}}$), we determine two possible ways in which the absolute $\rho _{ {met,neu}}$ observed in DLAs at high redshift can be matched by simulations: (i) the $\rho _{ {\rm {\small {sfr}}}}$ at $z$ ≳ 3 is greater than inferred from current FUV observations, or (ii) current high-redshift DLA metallicity samples have a higher mean host mass than the overall galaxy population. If the first is correct, TNG100 would match the ensemble data best, however there would be an outstanding tension between the currently observed $\rho _{ {\rm {\small {sfr}}}}$ and $\rho _{ {met,neu}}$. If the second is correct, L-Galaxies 2020 would match the ensemble data best, but would require an increase in neutral gas mass inside subhaloes above $z$ ∼ 2.5. If neither is correct, EAGLE would match the ensemble data best, although at the expense of overestimating $[\langle {} {M/H}\rangle ]_{ {neu}}$. Modulo details related to numerical resolution and H i mass modelling in simulations, these incompatibilities highlight current tensions between key observed cosmic properties at high redshift.

Simulating the infrared sky with a SPRITZ

Aims. Current hydrodynamical and semi-empirical simulations of galaxy formation and evolution have difficulties in reproducing the number densities of infrared-detected galaxies. Therefore, a phenomenological simulation tool that is new and versatile is necessary to reproduce current and predict future observations at infrared (IR) wavelengths. Methods. In this work we generate simulated catalogues starting from the Herschel IR luminosity functions of different galaxy populations to consider different populations of galaxies and active galactic nuclei (AGN) in a consistent way. We associated a spectral energy distribution and physical properties, such as stellar mass, star formation rate, and AGN contribution, with each simulated galaxy using a broad set of empirical relations. We compared the resulting simulated galaxies, extracted up to z = 10, with a broad set of observational relations. Results. Spectro-Photometric Realisations of IR-Selected Targets at all-z (SPRITZ) simulations allow us to obtain, in a fully consistent way, simulated observations for a broad set of current and future facilities with photometric capabilities as well as low-resolution IR spectroscopy, such as the James Webb Space Telescope (JWST) or the Origin Space Telescope (OST). The derived simulated catalogue contains galaxies and AGN that by construction reproduce the observed IR galaxy number density, but this catalogue also agrees with the observed number counts from UV to far-IR wavelengths, the observed stellar mass function, the star formation rate versus stellar mass plane, and the luminosity function from the radio to X-ray wavelengths. The proposed simulation is therefore ideal to make predictions for current and future facilities, in particular, but not limited to, those operating at IR wavelengths.

The galaxy H i–(sub)halo connection and the H i spatial clustering of local galaxies

ABSTRACT We extend the local stellar galaxy–(sub)halo connection to the atomic hydrogen (H i) component by seeding semi-empirically galaxies into a large N-body dark matter (DM) simulation. The main input to construct the mock galaxy catalogue are: our constrained stellar mass-to-(sub)halo circular velocity (M*–VDM) relation, assuming a scatter independent of any galaxy property, and the empirical $M_{\rm H\, \small {I}}$ conditional probability distributions given M* for central and satellite galaxies. We find that the $\langle \log \mbox{$M_{\rm H\, \small {I}}$}\rangle -\log \mbox{$M_{\rm DM}$}$ relation is not a monotonic increasing function. It increases with mass up to $\mbox{$M_{\rm DM}$}\sim 10^{12}$ M⊙, attaining a maximum of $\langle \log (\mbox{$M_{\rm H\, \small {I}}$}/\mbox{M$_{\odot }$})\rangle \sim 9.2$, and at higher (sub)halo masses, $\langle \log (\mbox{$M_{\rm H\, \small {I}}$})\rangle$ decreases slightly with MDM. The scatter around it is also large and mass dependent. The bivariate $M_{\rm H\, \small {I}}$ and MDM distribution is broad and bimodal, specially at $\mbox{$M_{\rm DM}$}\gtrsim 10^{12}$ M⊙, which is inherited from the input $M_{\rm H\, \small {I}}$ conditional distributions. We also report the total (central+satellites) H i gas mass within haloes, $M^{\rm tot}_{\rm H\, \small {I}}$, as a function of MDM. The mean $\mbox{$M^{\rm tot}_{\rm H\, \small {I}}$}$–$\mbox{$M_{\rm DM}$}$ relation is an increasing monotonic function. The galaxy spatial clustering increases weakly as the $M_{\rm H\, \small {I}}$ threshold increases. Our H i mock galaxies cluster more in comparison to the blind H i ALFALFA (Arecibo Fast Legacy ALFA) survey but we show that it is mainly due to the selection effects. We discuss the implications of our results in the light of predictions from semi-analytical models and hydrodynamics simulations of galaxy evolution.

Cosmic-Ray Transport, Energy Loss, and Influence in the Multiphase Interstellar Medium

Abstract The bulk propagation speed of GeV-energy cosmic rays is limited by frequent scattering off hydromagnetic waves. Most galaxy evolution simulations that account for this confinement assume the gas is fully ionized and cosmic rays are well coupled to Alfvén waves; however, multiphase density inhomogeneities, frequently underresolved in galaxy evolution simulations, induce cosmic-ray collisions and ionization-dependent transport driven by cosmic-ray decoupling and elevated streaming speeds in partially neutral gas. How do cosmic rays navigate and influence such a medium, and can we constrain this transport with observations? In this paper, we simulate cosmic-ray fronts impinging upon idealized, partially neutral clouds and lognormally distributed clumps, with and without ionization-dependent transport. With these high-resolution simulations, we identify cloud interfaces as crucial regions where cosmic-ray fronts can develop a stairstep pressure gradient sufficient to collisionlessly generate waves, overcome ion–neutral damping, and exert a force on the cloud. We find that the acceleration of cold clouds is hindered by only a factor of a few when ionization-dependent transport is included, with additional dependencies on magnetic field strength and cloud dimensionality. We also probe how cosmic rays sample the background gas and quantify collisional losses. Hadronic gamma-ray emission maps are qualitatively different when ionization-dependent transport is included, but the overall luminosity varies by only a small factor, as the short cosmic-ray residence times in cold clouds are offset by the higher densities that cosmic rays sample.

Revisiting the tension between fast bars and the ΛCDM paradigm

The pattern speed with which galactic bars rotate is intimately linked to the amount of dark matter in the inner regions of their host galaxies. In particular, dark matter haloes act to slow down bars via torques exerted through dynamical friction. Observational studies of barred galaxies tend to find that bars rotate fast, while hydrodynamical cosmological simulations of galaxy formation and evolution in the Lambda cold dark matter (ΛCDM) framework have previously found that bars slow down excessively. This has led to a growing tension between fast bars and the ΛCDM cosmological paradigm. In this study we revisit this issue, using the Auriga suite of high-resolution, magneto-hydrodynamical cosmological zoom-in simulations of galaxy formation and evolution in the ΛCDM framework, finding that bars remain fast down to z = 0. In Auriga, bars form in galaxies that have higher stellar-to-dark matter ratios and are more baryon-dominated than in previous cosmological simulations; this suggests that in order for bars to remain fast, massive spiral galaxies must lie above the commonly used abundance matching relation. While this reduces the aforementioned tension between the rotation speed of bars and ΛCDM, it accentuates the recently reported discrepancy between the dynamically inferred stellar-to-dark matter ratios of massive spirals and those inferred from abundance matching. Our results highlight the potential of using bar dynamics to constrain models of galaxy formation and evolution.

Lyman-alpha radiation pressure: an analytical exploration

ABSTRACT We study radiation pressure due to Ly α line photons, obtaining and exploring analytical expressions for the force-multiplier, MF(NH, Z) = Fα/(Lα/c), as a function of gas column density, NH, and metallicity, Z, for both dust-free and dusty media, employing a WKB approach for the latter case. Solutions for frequency offset emission to emulate non-static media moving with a bulk velocity v have also been obtained. We find that, in static media, Ly α pressure dominates over both photoionization and dust-mediated UV radiation pressure in a very wide parameter range (16 < log NH < 23; −4 < log [Z/Z⊙] < 0). For example, it overwhelms the other two forces by $\lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}10$ (300) times in standard (low-Z) star-forming clouds. Thus, in agreement with previous studies, we conclude that Ly α pressure plays a dominant role in the initial acceleration of the gas around luminous sources, and must be implemented in galaxy formation, evolution and outflow models and simulations.

A Graphical Interpretation of Circumgalactic Precipitation

Abstract Both observations and recent numerical simulations of the circumgalactic medium (CGM) support the hypothesis that a self-regulating feedback loop suspends the gas density of the ambient CGM close to the galaxy in a state with a ratio of cooling time to freefall time ≳10. This limiting ratio is thought to arise because circumgalactic gas becomes increasingly susceptible to multiphase condensation as the ratio declines. If the timescale ratio gets too small, then cold clouds precipitate out of the CGM, rain into the galaxy, and fuel energetic feedback that raises the ambient cooling time. The astrophysical origin of this so-called precipitation limit is not simple but is critical to understanding the CGM and its role in galaxy evolution. This paper therefore attempts to interpret its origin as simply as possible, relying mainly on conceptual reasoning and schematic diagrams. It illustrates how the precipitation limit can depend on both the global configuration of a galactic atmosphere and the degree to which dynamical disturbances drive CGM perturbations. It also frames some tests of the precipitation hypothesis that can be applied to both CGM observations and numerical simulations of galaxy evolution.

3-3-1 Self interacting dark matter and the galaxy core-cusp problem

The core–cusp problem remains a challenging discrepancy between observations and simulations in the standard [Formula: see text]CDM model for the formation of galaxies. The problem is that [Formula: see text]CDM simulations predict a steep power-law mass density profile at the center of galactic dark matter halos. However, observations of dwarf galaxies in the Local Group reveal a density profile consistent with a nearly flat distribution of dark matter near the center. A number of solutions to this dilemma have been proposed. Here, we summarize investigations into the possibility that the dark matter particles themselves self interact and scatter. Such self-interacting dark matter (SIDM) particles can smooth out the dark-matter profile in high-density regions. We also review the theoretical proposal that self-interacting dark matter may arise as an additional Higgs scalar in the 3–3–1 extension of the Standard Model (SM). We present new simulations of galaxy formation and evolution for this formulation of self-interacting dark matter. Current constraints on this self-interacting dark matter are then summarized.

The Assembly History of M87 through Radial Variations in Chemical Abundances of Its Field Star and Globular Cluster Populations

Abstract We present an extensive study of spectroscopically derived chemical abundances for M87 and its globular cluster (GC) system. Using observations from the Mitchell spectrograph at McDonald, LRIS at Keck, and Hectospec on the MMT, we derive new metallicity gradients from ∼2 to 140 kpc. We use a novel hierarchical statistical framework to simultaneously separate the GC system into subpopulations while measuring the metallicity gradients of those subpopulations. We create physically motivated spectral stacks of the GC subpopulations by leveraging the output of this statistical framework to perform the first application of abundance tagging in a massive early-type galaxy to better constrain the origins of the GC subpopulations and thus the assembly history of M87. We find a metal-poor, α-enhanced population of GCs in both the inner and outer halos unanticipated by current cosmological simulations of galaxy evolution. We use the remarkably flat metallicity gradients we find for both the metal-rich and metal-poor GC subpopulations in the inner halo as tentative evidence that some amount of the metal-poor GCs formed directly in the halo of M87 at high redshift.

Powering galactic superwinds with small-scale AGN winds

ABSTRACT We present a new implementation for active galactic nucleus (AGN) feedback through small-scale, ultrafast winds in the moving-mesh hydrodynamic code arepo. The wind is injected by prescribing mass, momentum, and energy fluxes across a spherical boundary centred on a supermassive black hole according to available constraints for accretion disc winds. After sweeping-up a mass equal to their own, small-scale winds thermalize, powering energy-driven outflows with dynamics, structure, and cooling properties in excellent agreement with those of analytic wind solutions. Momentum-driven solutions do not easily occur, because the Compton cooling radius is usually much smaller than the free-expansion radius of the small-scale winds. Through various convergence tests, we demonstrate that our implementation yields wind solutions, which are well converged down to the typical resolution achieved in cosmological simulations. We test our model in hydrodynamic simulations of isolated Milky Way – mass galaxies. Above a critical AGN luminosity, initially spherical, small-scale winds power bipolar, energy-driven superwinds that break out of the galactic nucleus, flowing at speeds $\gt 1000 \rm \, km \, s^{-1}$ out to $\sim 10 \, \rm kpc$. These energy-driven outflows result in moderate, but long-term, reduction in star formation, which becomes more pronounced for higher AGN luminosities and faster small-scale winds. Suppression of star formation proceeds through a rapid mode that involves the removal of the highest density, nuclear gas, and through a slower mode that effectively halts halo gas accretion. Our new implementation makes it possible to model AGN-driven winds in a physically meaningful and validated way in simulations of galaxy evolution, the interstellar medium and black hole accretion flows.

An Accreting, Anomalously Low-mass Black Hole at the Center of Low-mass Galaxy IC 750

Abstract We present a multiwavelength study of the active galactic nucleus in the nearby (D = 14.1 Mpc) low-mass galaxy IC 750, which has circumnuclear 22 GHz water maser emission. The masers trace a nearly edge-on, warped disk ∼0.2 pc in diameter, coincident with the compact nuclear X-ray source that lies at the base of the ∼kiloparsec-scale extended X-ray emission. The position–velocity structure of the maser emission indicates that the central black hole (BH) has a mass less than 1.4 × 105 M ⊙. Keplerian rotation curves fitted to these data yield enclosed masses between 4.1 × 104 M ⊙ and 1.4 × 105 M ⊙, with a mode of 7.2 × 104 M ⊙. Fitting the optical spectrum, we measure a nuclear stellar velocity dispersion km s−1. From near-infrared photometry, we fit a bulge mass of (7.3 ± 2.7) × 108 M ⊙ and a stellar mass of 1.4 × 1010 M ⊙. The mass upper limit of the intermediate-mass BH in IC 750 falls roughly two orders of magnitude below the M BH–σ * relation and roughly one order of magnitude below the M BH–M Bulge and M BH–M * relations—larger than the relations’ intrinsic scatters of 0.58 ± 0.09 dex, 0.69 dex, and 0.65 ± 0.09 dex, respectively. These offsets could be due to larger scatter at the low-mass end of these relations. Alternatively, BH growth is intrinsically inefficient in galaxies with low bulge and/or stellar masses, which causes the BHs to be undermassive relative to their hosts, as predicted by some galaxy evolution simulations.