Co-evolution Of Galaxies Research Articles

X-ray observations of luminous dusty quasars at z > 2

ABSTRACT We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared (IR) sky surveys. HRQs appear to be a dominant population at high redshifts and the highest luminosities, and may be associated with a transitional ‘blowout’ phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of 10 objects with XMM–Newton coverage to study the high-energy properties of HRQs at $\langle$Lbol$\rangle$ =1047.5 erg s−1 and $\langle$z$\rangle$ =2.5. For seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $\left\langle L_{\rm 2\!-\!10\, keV} \right\rangle = 10^{45.1}$ erg s−1, comparable to the most powerful X-ray quasars known. The gas column densities are NH = (1–8) × 1022 cm−2, in agreement with the amount of dust extinction observed. The dust-to-gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-IR ($L_{\rm 6\, \mu m}$) and bolometric luminosities (Lbol), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from κbol ≈ 50 to 3000. The moderate absorption levels and accretion rates close to the Eddington limit ($\langle$λEdd$\rangle$ =1.06) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the NH–λEdd plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few 105 yr. The wider properties, including [O iii] narrow-line region kinematics, broadly agree with this interpretation.

Stochastic Processes as the Origin of the Double Power-law Shape of the Quasar Luminosity Function

Abstract The quasar luminosity function (QLF) offers insight into the early coevolution of black holes and galaxies. It has been characterized observationally up to redshift z ∼ 6 with clear evidence of a double power-law shape, in contrast to the Schechter-like form of the underlying dark-matter halo mass function. We investigate a physical origin for the difference in these distributions by considering the impact of stochasticity induced by the processes that determine the quasar luminosity for a given host halo and redshift. We employ a conditional luminosity function and construct the relation between median quasar magnitude versus halo mass with log-normal in luminosity scatter Σ, and duty-cycle ϵ DC, and focus on high redshift z ≳ 4. We show that, in order to reproduce the observed QLF, the Σ = 0 abundance matching requires all of the brightest quasars to be hosted in the rarest most massive dark-matter halos (with an increasing in halo mass). Conversely, for Σ > 0 the brightest quasars can be overluminous outliers hosted in relatively common dark-matter halos. In this case, the median quasar magnitude versus halo mass relation, M UV,c, flattens at the high-end, as expected in self-regulated growth due to feedback. We sample the parameter space of Σ and ϵ DC and show that M UV,c flattens above for . Models with ϵ DC ∼ 1 instead require a high mass threshold close to . We investigate the impact of ϵ DC and Σ on measurements of clustering and find there is no luminosity dependence on clustering for Σ > 0.3, consistent with recent observations from Subaru HSC.

A parsec-scale radio jet launched by the central intermediate-mass black hole in the dwarf galaxy SDSS J090613.77+561015.2

ABSTRACT The population of intermediate-mass black holes (IMBHs) in nearby dwarf galaxies plays an important ‘ground truth’ role in exploring black hole formation and growth in the early Universe. In the dwarf elliptical galaxy SDSS J090613.77+561015.2 (z = 0.0465), an accreting IMBH has been revealed by optical and X-ray observations. Aiming to search for possible radio core and jet associated with the IMBH, we carried out very long baseline interferometry (VLBI) observations with the European VLBI Network at 1.66 GHz. Our imaging results show that there are two 1-mJy components with a separation of about 52 mas (projected distance 47 pc) and the more compact component is located within the 1σ error circle of the optical centroid from available Gaia astrometry. Based on their positions, elongated structures and relatively high brightness temperatures, as well as the absence of star-forming activity in the host galaxy, we argue that the radio morphology originates from the jet activity powered by the central IMBH. The existence of the large-scale jet implies that violent jet activity might occur in the early epochs of black hole growth and thus help to regulate the co-evolution of black holes and galaxies.

An X‐ray view of the hot circum‐galactic medium

AbstractThe hot circum‐galactic medium (CGM) represents the hot gas distributed beyond the stellar content of the galaxies while typically within their dark matter halos. It serves as a depository of energy and metal‐enriched materials from galactic feedback and a reservoir from which the galaxy acquires fuels to form stars. It thus plays a critical role in the coevolution of galaxies and their environments. X‐rays are one of the best ways to trace the hot CGM. I will briefly review what we have learned about the hot CGM based on X‐ray observations over the past two decades, and what we still do not know. I will also briefly prospect what may be the foreseeable breakthrough in the next one or two decades with future X‐ray missions.

The importance of special relativistic effects in modelling ultra-fast outflows

Context. Outflows are observed in a variety of astrophysical sources. Remarkably, ultra-fast (v ≥ 0.1c), highly ionised outflows in the UV and X-ray bands are often seen in active galactic nuclei (AGNs). Depending on their kinetic power and mass outflow rate, Ėout and Ṁout, respectively, these outflows may play a key role in regulating the AGN–host galaxy co-evolution process through cosmic time and metal-feeding the surrounding circum-/inter-galactic medium. It is therefore crucial to provide accurate estimates of the wind properties, including Ṁout and Ėout. Aims. Here we concentrate on special relativistic effects concerning the interaction of light with matter moving at relativistic speed relatively to the source of radiation. Our aim is to assess the impact of these effects on the observed properties of the outflows and implement a correction for these effects in the existing spectral modelling routines. Methods. We define a simple procedure to incorporate relativistic effects in radiative transfer codes. Following this procedure, we run a series of simulations to explore the impact of relativistic effects for different outflow velocities and column densities. Results. The observed optical depth of the wind is usually considered a proxy for its column density NH, independently of the velocity of the outflow. However, our simulations show that the observed optical depth of an outflow with a given NH decreases rapidly as the velocity of the wind approaches relativistic values. This, in turn, implies that when estimating NH from the optical depth, it is necessary to include a velocity-dependent correction, already for moderate velocities (e.g. vout ≳ 0.05c). This correction linearly propagates to the derived quantities Ṁout and Ėout. Conclusions. We demonstrate that special relativistic effects must be considered in order to obtain correct estimates of Ṁout and Ėout for an outflow moving at a mildly relativistic speed relative to the illuminating source of radiation. As an example, we calculate the relativistically corrected values of Ṁout and Ėout for a sample of ∼30 ultra-fast outflows (UFOs) taken from the literature and find correction factors of 20 − 120% within the observed range of outflowing velocities (vout ≈ 0.1 − 0.3c). This brings the ratio between Ṁout and the disc accretion rate close or even above unity for the vast majority of the sources of the sample, highlighting the importance of the reported relativistic corrections to understand the growth of the most massive black holes. The next generation of high-sensitivity X-ray telescopes such as XRISM and Athena will provide a much more complete census of UFOs, especially in the fastest velocity regime where the relativistic corrections are increasingly important.

Spin evolution and feedback of supermassive black holes in cosmological simulations

ABSTRACT It is well established that the properties of supermassive black holes (BHs) and their host galaxies are correlated through scaling relations. While hydrodynamical cosmological simulations have begun to account for the coevolution of BHs and galaxies, they typically have neglected the BH spin, even though it may play an important role in modulating the growth and feedback of BHs. Here we introduce a new sub-grid model for the BH spin evolution in the moving-mesh code arepo in order to improve the physical faithfulness of the BH modelling in galaxy formation simulations. We account for several different channels of spin evolution, in particular gas accretion through a Shakura–Sunyaev α-disc, chaotic accretion, and BH mergers. For BH feedback, we extend the IllustrisTNG model, which considers two different BH feedback modes, a thermal quasar mode for high accretion states and a kinetic mode for low Eddington ratios, with a self-consistent accounting of spin-dependent radiative efficiencies and thus feedback strength. We find that BHs with a mass $M_{\mbox{{bh}}}\lesssim 10^{8}\, {\rm M}_{\odot }$ reach high spin values as they typically evolve in the coherent gas accretion regime, in which consecutive accretion episodes are aligned. On the other hand, BHs with a mass $M_{\mbox{{bh}}}\gtrsim 10^{8}\, {\rm M}_{\odot }$ have lower spins as BH mergers become more frequent, and their accretion discs fragment due to self-gravity, inducing chaotic accretion. We also explore the hypothesis that the transition between the quasar and kinetic feedback modes is mediated by the accretion mode of the BH disc itself, i.e. the kinetic feedback mode is activated when the disc enters the self-gravity regime instead of by an ad hoc switch tied to the BH mass. We find excellent agreement between the galaxy and BH populations for this approach and the fiducial TNG model with no spin evolution. Furthermore, our new approach alleviates a tension in the galaxy morphology–colour relation of the original TNG model.

The CGM–GRB Study. I. Uncovering the Circumgalactic Medium around GRB Hosts at Redshifts 2–6

Abstract Recent studies have revealed a dynamic interplay between the galaxy ecosystem and circumgalactic medium (CGM). We investigate the CGM at high redshifts (z ≳ 2) by using bright afterglows of gamma-ray bursts (GRBs) as background sources. We compiled a sample of medium-resolution (Δv < 50 km s−1) and high signal-to-noise ratio (typical S/N ∼ 10) spectra from 27 GRB afterglows covering z ∼ 2–6, with six of them at z ≳ 4. We analyzed the high- and low-ionization absorption features within ±400 km s−1 to extract the CGM and interstellar medium (ISM) kinematics. In the stacked spectra, high-ionization absorption profiles (e.g., C iv, Si iv) present significant absorption excess in their blue wings (v < −100 km s−1) relative to the red wings (v > 100 km s−1). The stronger blue wings in high-ionization species are indicative of the presence of ubiquitous warm outflows in the GRB hosts at high redshifts. We used simple toy models to kinematically distinguish the CGM and ISM absorption and estimate the CGM mass and outflow velocity. We find tentative evidence of the evolution of the CGM metal mass by ∼0.5 dex between two redshift bins, each spanning 1 Gyr, z1: 2–2.7 and z2: 2.7–5. By comparing with past studies, we find that over the course of evolution of present-day galaxies with M * > 1010 M ⊙, the ratio of C iv mass in the CGM to the stellar mass remains fairly uniform, with log(M C iv /M *) ∼ −4.5 within ±0.5 dex from z ∼ 4 to z ∼ 0, suggesting CGM–galaxy coevolution.

A Triple AGN in a Mid-infrared Selected Late-stage Galaxy Merger

Abstract The coevolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of ΛCDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations <10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Paα detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the “Final Parsec Problem.” AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally bound triple phase.

Probing black hole - host galaxy scaling relations with obscured type II AGN

AbstractThe scaling relations between supermassive black holes and their host galaxy properties are of fundamental importance in the context black hole-host galaxy co-evolution throughout cosmic time. Beyond the local universe, such relations are based on black hole mass estimates in type I AGN. Unfortunately, for this type of objects the host galaxy properties are more difficult to obtain since the AGN dominates the observed flux in most wavelength ranges. In this poster I will present a new correlation we discovered between the narrow L([OIII])/L(Hβ) line ratio and the FWHM(broad Hα). This scaling relation ties the kinematics of the gas clouds in the broad line region to the ionization state of gas in the narrow line region, connecting the properties of gas clouds kiloparsecs away from the black hole to material gravitationally bound to it on sub-parsec scales. This relation can be used to estimate black hole masses from narrow emission lines only, and thus brings the missing piece required to estimate black hole masses in obscured type II AGN. Using this technique, we estimate the black hole mass of about 10,000 type II AGN, and present, for the first time, M(BH)-sigma and M(BH)-M(stars) scaling relations for this population. These relations are remarkably consistent with those observed for type I AGN, suggesting that this new method may perform as reliably as the classical estimate used in non-obscured type I AGN. These findings open a new window for studies of black hole-host galaxy co-evolution throughout cosmic time.

Does black hole growth depend fundamentally on host-galaxy compactness?

ABSTRACT Possible connections between central black hole (BH) growth and host-galaxy compactness have been found observationally, which may provide insight into BH–galaxy coevolution: compact galaxies might have large amounts of gas in their centres due to their high mass-to-size ratios, and simulations predict that high central gas density can boost BH accretion. However, it is not yet clear if BH growth is fundamentally related to the compactness of the host galaxy, due to observational degeneracies between compactness, stellar mass (M⋆) and star formation rate (SFR). To break these degeneracies, we carry out systematic partial-correlation studies to investigate the dependence of sample-averaged BH accretion rate ($\rm \overline{BHAR}$) on the compactness of host galaxies, represented by the surface-mass density, Σe, or the projected central surface-mass density within 1 kpc, Σ1. We utilize 8842 galaxies with H < 24.5 in the five CANDELS fields at z = 0.5–3. We find that $\rm \overline{BHAR}$ does not significantly depend on compactness when controlling for SFR or M⋆ among bulge-dominated galaxies and galaxies that are not dominated by bulges, respectively. However, when testing is confined to star-forming galaxies at z = 0.5–1.5, we find that the $\rm \overline{BHAR}$–Σ1 relation is not simply a secondary manifestation of a primary $\rm \overline{BHAR}$–M⋆ relation, which may indicate a link between BH growth and the gas density within the central 1 kpc of galaxies.

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). VIII. A less biased view of the early co-evolution of black holes and host galaxies

Abstract We present ALMA [C ii] line and far-infrared (FIR) continuum observations of three $z \gt 6$ low-luminosity quasars ($M_{\rm 1450} \gt -25$ mag) discovered by our Subaru Hyper Suprime-Cam (HSC) survey. The [C ii] line was detected in all three targets with luminosities of $(2.4\mbox{--}9.5) \times 10^8\, L_{\odot }$, about one order of magnitude smaller than optically luminous ($M_{\rm 1450} \lesssim -25$ mag) quasars. The FIR continuum luminosities range from $\lt 9 \times 10^{10}\, L_{\odot }$ (3 $\sigma$ limit) to ${\sim } 2 \times 10^{12}\, L_{\odot }$, indicating a wide range in star formation rates in these galaxies. Most of the HSC quasars studied thus far show [C ii]/ FIR luminosity ratios similar to local star-forming galaxies. Using the [C ii]-based dynamical mass ($M_{\rm dyn}$) as a surrogate for bulge stellar mass ($M_{\rm\, bulge}$), we find that a significant fraction of low-luminosity quasars are located on or even below the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation, particularly at the massive end of the galaxy mass distribution. In contrast, previous studies of optically luminous quasars have found that black holes are overmassive relative to the local relation. Given the low luminosities of our targets, we are exploring the nature of the early co-evolution of supermassive black holes and their hosts in a less biased way. Almost all of the quasars presented in this work are growing their black hole mass at a much higher pace at $z \sim 6$ than the parallel growth model, in which supermassive black holes and their hosts grow simultaneously to match the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation at all redshifts. As the low-luminosity quasars appear to realize the local co-evolutionary relation even at $z \sim 6$, they should have experienced vigorous starbursts prior to the currently observed quasar phase to catch up with the relation.

Tracing black hole and galaxy co-evolution in the Romulus simulations

ABSTRACT We study the link between supermassive black hole growth and the stellar mass assembly of their host galaxies in the state-of-the-art Romulus suite of simulations. The cosmological simulations Romulus25 and RomulusC employ innovative recipes for the seeding, accretion, and dynamics of black holes in the field and cluster environments, respectively. We find that the black hole accretion rate traces the star formation rate among star-forming galaxies. This result holds for stellar masses between 108 and 1012 solar masses, with a very weak dependence on host halo mass or redshift. The inferred relation between accretion rate and star formation rate does not appear to depend on environment, as no difference is seen in the cluster/proto-cluster volume compared to the field. A model including the star formation rate, the black hole-to-stellar mass ratio, and the cold gas fraction can explain about 70 per cent of all variations in the black hole accretion rate among star-forming galaxies. Finally, bearing in mind the limited volume and resolution of these cosmological simulations, we find no evidence for a connection between black hole growth and galaxy mergers, on any time-scale and at any redshift. Black holes and their galaxies assemble in tandem in these simulations, regardless of the larger scale intergalactic environment, suggesting that black hole growth simply follows star formation on galactic scales.

Black hole – Galaxy correlations in simba

ABSTRACT We examine the co-evolution of galaxies and supermassive black holes in the simba cosmological hydrodynamic simulation. simba grows black holes via gravitational torque-limited accretion from cold gas and Bondi accretion from hot gas, while feedback from black holes is modelled in radiative and jet modes depending on the Eddington ratio (fEdd). simba shows generally good agreement with local studies of black hole properties, such as the black hole mass–stellar velocity dispersion (MBH–σ) relation, the black hole accretion rate versus star formation rate (BHAR–SFR), and the black hole mass function. MBH–σ evolves such that galaxies at a given MBH have higher σ at higher redshift, consistent with no evolution in MBH–M⋆. For $M_{\rm BH}\lesssim 10^8\, {\rm M}_{\odot }$, fEdd is anticorrelated with MBH since the BHAR is approximately independent of MBH, while at higher masses fEdd–MBH flattens and has a larger scatter. BHAR versus SFR is invariant with redshift, but fEdd drops steadily with time at a given MBH, such that all but the most massive black holes are accreting in a radiatively efficient mode at $z\gtrsim 2$. The black hole mass function amplitude decreases with redshift and is locally dominated by quiescent galaxies for MBH > 108 M⊙, but for $z\gtrsim 1$ star-forming galaxies dominate at all MBH. The z = 0 fEdd distribution is roughly lognormal with a peak at $f_{\rm Edd}\lesssim 0.01$ as observed, shifting to higher fEdd at higher redshifts. Finally, we study the dependence of black hole properties with H i content and find that the correlation between gas content and SFR is modulated by black hole properties, such that higher SFR galaxies at a given gas content have smaller black holes with higher fEdd.

A Giant Intragroup Nebula Hosting a Damped Absorber at z = 0.313

Abstract This Letter reports the discovery of spatially extended line-emitting nebula, reaching to ≈100 physical kpc (pkpc) from a damped absorber (DLA) at z DLA = 0.313 along the sightline toward quasi-stellar object (QSO) PKS 1127−145 (z QSO = 1.188). This DLA was known to be associated with a galaxy group of dynamical mass M group ∼ 3 × 1012 M ⊙, but its physical origin remained ambiguous. New wide-field integral field observations revealed a giant nebula detected in [O ii], Hβ, [O iii], Hα, and [N ii] emission, with the line-emitting gas following closely the motions of group galaxies. One of the denser streams passes directly in front of the QSO with kinematics that are consistent with the absorption profiles recorded in the QSO echelle spectra. The emission morphology, kinematics, and line ratios of the nebula suggest that shocks and turbulent mixing layers, produced as a result of stripped gaseous streams moving at supersonic speed across the ambient hot medium, contribute significantly to the ionization of the gas. While the DLA may not be associated with any specific detected member of the group, both the kinematic and dust properties are consistent with the DLA originating in streams of gas stripped from sub-L * group members at ≲25 pkpc from the QSO sightline. This study demonstrates that gas stripping in low-mass galaxy groups is effective in releasing metal-enriched gas from star-forming regions, producing absorption systems in QSO spectra, and that combining absorption and emission-line observations provides an exciting new opportunity for studying gas and galaxy co-evolution.

Supermassive black hole demographics: evading M − σ

We consider black hole - galaxy coevolution using simple analytic arguments. We focus on the fact that several supermassive black holes are known with masses significantly larger than suggested by the $M - {\sigma}$ relation, sometimes also with rather small stellar masses. We show that these are likely to have descended from extremely compact `blue nugget' galaxies born at high redshift, whose very high velocity dispersions allowed the black holes to reach unusually large masses. Subsequent interactions reduce the velocity dispersion, so the black holes lie above the usual $M - {\sigma}$ relation and expel a large fraction of the bulge gas (as in WISE J104222.11+164115.3) that would otherwise make stars, before ending at low redshift as very massive holes in galaxies with relatively low stellar masses, such as NGC 4889 and NGC 1600. We further suggest the possible existence of two new types of galaxy: low-mass dwarfs whose central black holes lie below the $M - {\sigma}$ relation at low redshift, and galaxies consisting of very massive ($\gtrsim 10^{11}$M$_{\odot}$) black holes with extremely small stellar masses. This second group would be very difficult to detect electromagnetically, but potentially offer targets of considerable interest for LISA.

Black hole mass estimation for active galactic nuclei from a new angle

Abstract The scaling relations between supermassive black holes and their host galaxy properties are of fundamental importance in the context black hole-host galaxy co-evolution throughout cosmic time. In this work, we use a novel algorithm that identifies smooth trends in complex data sets and apply it to a sample of 2000 type 1 active galactic nuclei (AGNs) spectra. We detect a sequence in emission line shapes and strengths which reveals a correlation between the narrow L([O iii])/L(H β) line ratio and the width of the broad H α. This scaling relation ties the kinematics of the gas clouds in the broad line region to the ionization state of the narrow line region, connecting the properties of gas clouds kiloparsecs away from the black hole to material gravitationally bound to it on sub-parsec scales. This relation can be used to estimate black hole masses from narrow emission lines only. It therefore enables black hole mass estimation for obscured type 2 AGNs and allows us to explore the connection between black holes and host galaxy properties for thousands of objects, well beyond the local Universe. Using this technique, we present the MBH–σ and MBH–M* scaling relations for a sample of about 10 000 type 2 AGNs from Sloan Digital Sky Survey. These relations are remarkably consistent with those observed for type 1 AGNs, suggesting that this new method may perform as reliably as the classical estimate used in non-obscured type 1 AGNs. These findings open a new window for studies of black hole-host galaxy co-evolution throughout cosmic time.

A rapidly evolving quasar population at the epoch of reionzation

AbstractI will present results from our on-going large area survey of high-redshift quasars, which has discovered more than 20 new quasars at z > 6.5, at the epoch of reionization, forming the first large statistical sample of EoR quasars. I will discuss the rapid evolution of quasar density at that epoch, which suggests that we are witnessing the emergence of the first supermassive black hole population. I will also present multiwavelength followup observation results, especially from ALMA and Chandra, which reveals a diverse environment of quasar activities and yields new insights into the supermassive black hole/massive galaxy co-evolution.

Coevolution (or not) of supermassive black holes and host galaxies: Black hole scaling relations are not biased by selection effects

AbstractThe oral version of this paper summarized Kormendy & Ho 2013, ARA&A, 51, 511. However, earlier speakers at this Symposium worried that selection effects bias the derivation of black hole scaling relations. I therefore added – and this proceedings paper emphasizes – a discussion of why we can be confident that selection effects do not bias the observed correlations between BH mass M• and the luminosity, stellar mass, and velocity dispersion of host ellipticals and classical bulges. These are the only galaxy components that show tight BH-host correlations. The scatter plots of M• with host properties for pseudobulges and disks are upper envelopes of scatter that does extend to lower BH masses. BH correlations are most consistent with a picture in which BHs coevolve only with classical bulges and ellipticals. Four physical regimes of coevolution (or not) are suggested by Kormendy & Ho 2013 and are summarized here.

The E-MOSAICS project: tracing galaxy formation and assembly with the age–metallicity distribution of globular clusters

We present 25 cosmological zoom-in simulations of Milky-Way-mass galaxies in the ‘MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE’ (E-MOSAICS) project. E-MOSAICS couples a detailed physical model for the formation, evolution, and disruption of star clusters to the EAGLE galaxy formation simulations. This enables following the co-formation and co-evolution of galaxies and their star cluster populations, thus realizing the long-standing promise of using globular clusters (GCs) as tracers of galaxy formation and assembly. The simulations show that the age–metallicity distributions of GC populations exhibit strong galaxy-to-galaxy variations, resulting from differences in their evolutionary histories. We develop a formalism for systematically constraining the assembly histories of galaxies using GC age–metallicity distributions. These distributions are characterized through 13 metrics that we correlate with 30 quantities describing galaxy formation and assembly (e.g. halo properties, formation/assembly redshifts, stellar mass assembly time-scales, galaxy merger statistics), resulting in 20 statistically (highly) significant correlations. The GC age–metallicity distribution is a sensitive probe of the mass growth, metal enrichment, and minor merger history of the host galaxy. No such relation is found between GCs and major mergers, which play a sub-dominant role in GC formation for Milky-Way-mass galaxies. Finally, we show how the GC age–metallicity distribution enables the reconstruction of the host galaxy’s merger tree, allowing us to identify all progenitors with masses |$M_*\gtrsim 10^8\,{\rm M}_\odot$| for redshifts 1 ≤ z ≤ 2.5. These results demonstrate that cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies successfully unlock the potential of GCs as quantitative tracers of galaxy formation and assembly.

Testing the Evolutionary Link between Type 1 and Type 2 Quasars with Measurements of the Interstellar Medium

Abstract In a popular scenario for the coevolution of massive black holes and galaxies, major mergers of gas-rich galaxies fuel vigorous star formation and obscured (type 2) quasar activity until energy feedback from the active galactic nucleus (AGN) clears away the gas and dust to reveal an unobscured (type 1) quasar. Under this scenario, the precursor type 2 quasars should be more gas-rich than their type 1 counterparts, and both types of quasars are expected to be gas-deficient relative to normal, star-forming galaxies of similar stellar mass. We test this evolutionary hypothesis by investigating the infrared (∼1–500 μm) spectral energy distribution of 86 optically selected z < 0.5 type 2 quasars, matched in redshift and [O iii] luminosity to a comparison sample of type 1 quasars. Contrary to expectations, the gas content of the host galaxies of type 2 quasars is nearly indistinguishable from that of type 1 quasar hosts, and neither type exhibits the predicted deficit in gas relative to normal galaxies. The gas mass fraction of quasar hosts appears unaffected by the bolometric luminosity of the active nucleus, although their interstellar radiation field is preferentially higher than that of normal galaxies, potentially implicating AGN heating of the large-scale galactic dust.