A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. I. Galaxy Mergers and Quasar Activity

By P. Hopkins, L. Hernquist, Thomas J. Cox, D. Keres̆. 2007

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We develop a model for the cosmological role of mergers in the evolution of starbursts, quasars, and spheroidal galaxies. By combining theoretically well-constrained halo and subhalo mass functions as a function of redshift and environment with empirical halo occupation models, we can estimate where galaxies of given properties live at a particular epoch. This allows us to calculate, in an a priori cosmological manner, where major galaxy-galaxy mergers occur and what kinds of galaxies merge, at all redshifts. We compare this with the observed mass functions, clustering, fractions as a function of halo and galaxy mass, and small-scale environments of mergers, and we show that this approach yields robust estimates in good agreement with observations and can be extended to predict detailed properties of mergers. Making the simple Ansatz that major, gas-rich mergers cause quasar activity (but not strictly assuming they are the only triggering mechanism), we demonstrate that this model naturally reproduces the observed rise and fall of the quasar luminosity density at z = 0–6, as well as quasar luminosity functions, fractions, host galaxy colors, and clustering as a function of redshift and luminosity. The recent observed excess of quasar clustering on small scales at z ∼ 0.2–2.5 is a natural prediction of our model, as mergers will preferentially occur in regions with excess small-scale galaxy overdensities. In fact, we demonstrate that quasar environments at all observed redshifts correspond closely to the empirically determined small group scale, where major mergers of ~L* gas-rich galaxies will be most efficient. We contrast this with a secular model in which quasar activity is driven by bars or other disk instabilities, and we show that, while these modes of fueling probably dominate the high Eddington ratio population at Seyfert luminosities (significant at z = 0), the constraints from quasar clustering, observed pseudobulge populations, and disk mass functions suggest that they are a small contributor to the z ≳ 1 quasar luminosity density, which is dominated by massive BHs in predominantly classical spheroids formed in mergers. Similarly, low-luminosity Seyferts do not show a clustering excess on small scales, in agreement with the natural prediction of secular models, but bright quasars at all redshifts do so. We also compare recent observations of the colors of quasar host galaxies and show that these correspond to the colors of recent merger remnants, in the transition region between the blue cloud and the red sequence, and are distinct from the colors of systems with observed bars or strong disk instabilities. Even the most extreme secular models, in which all bulge (and therefore BH) formation proceeds via disk instability, are forced to assume that this instability acts before the (dynamically inevitable) mergers, and therefore predict a history for the quasar luminosity density that is shifted to earlier times, in disagreement with observations. Our model provides a powerful means to predict the abundance and nature of mergers and to contrast cosmologically motivated predictions of merger products such as starbursts and active galactic nuclei.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c97130e618d452f83351418727db4ee843fa1b2d

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THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES (2012, methodology): “This observed behavior is currently favored by models of mergerdriven AGN fueling (e.g., Hopkins et al. 2008), where the obscured accretion phase should happen in sources with an irregular morphology due to major mergers, suggesting that these models are valid in the high luminosity regime only.”
MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. II. PROPERTIES OF WISE-SELECTED ACTIVE GALACTIC NUCLEI IN THE NDWFS BOÖTES FIELD (2012, background): “It may be possible that in certain AGN feedback scenarios the column density of the residual dust in the ISM left after the AGN has gone through the blow-out phase (see, e.g., Hopkins et al. 2008) could be related to AGN luminosity during its quasar phase.”
Doing Science with eLISA: Astrophysics and Cosmology in the Millihertz Regime (2012, background): “The relation may have been established along the course of galactic mergers and in episodes of self-regulated accretion (Croton et al., 2006, Di Matteo et al., 2005, Hopkins et al., 2006, 2008, 2009, Johansson et al., 2009, Lamastra et al., 2010, Mihos and Hernquist, 1996, Somerville et al., 2008).”
The bolometric quasar luminosity function at z = 0–7 (2020, background): “…galaxies (e.g., Sanders & Mirabel 1996; Springel et al. 2005; Bower et al. 2006; Croton et al. 2006; Sijacki et al. 2007; Somerville et al. 2008; Hopkins et al. 2008; Feruglio et al. 2010; Fabian 2012; Cicone et al. 2014) and solve the classical "cooling flow" problem (e.g., Cowie & Binney…”
A general model for the CO–H2 conversion factor in galaxies with applications to the star formation law (2011, background): “…properties of metallicities in mergers (Cox et al. 2006a; Torrey et al. 2011), the broad-band colours of post-starburst galaxies (Snyder et al. 2011), and the structural properties of merging and elliptical galaxies (Hopkins et al. 2008c,d; Hopkins, Cox & Hernquist 2008a; Hopkins et al. 2009).”
THE ERA OF STAR FORMATION IN GALAXY CLUSTERS (2013, background): “In the local Universe, group environments, with their relatively high source densities and modest velocity dispersions, are expected to have the highest merging frequency (Hopkins et al. 2008).”
The mean star formation rate of X-ray selected active galaxies and its evolution from z~2.5: results from PEP-Herschel (2012, background): “These high luminosity, high accretionrate phases of SMBH growth are visible in their end stages as QSOs and evolutionary models of SMBH growth by mergers can explain simultaneously the form and evolution of empirical SMBH mass functions, QSO luminosity functions, merger and red galaxy density functi”
The Evolution of Galaxy Structure Over Cosmic Time (2014, background): “At the same time gas is driven to the centers of galaxies, producing active galactic nuclei (AGN) (e.g., Hopkins et al. 2008).”
Cosmic X-ray surveys of distant active galaxies (2015, background): “…AGNs are triggered by gas-rich major mergers, violent events where two similar-mass galaxies interact and merge, torquing the gas and driving it toward the central SMBH, where it can be accreted (e.g., Sanders et al 1988; Barnes and Hernquist 1992; Mihos and Hernquist 1996; Hopkins et al 2008).”
A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. II. Formation of Red Ellipticals (2007, background): “In Hopkins et al. (2008) we provide an outline of the phases of evolution that might be associated with amajor merger in the lifetime of a massive galaxy, but we briefly summarize them here.”
The WIRCam Deep Survey I. Counts, colours, and mass-functions derived from near-infrared imaging in the CFHTLS deep fields (2011, background): “These observations corroborate the picture of galaxy evolution whereby a massdependent shut-down of star formation is experienced by galaxies (e.g. Hopkins et al. 2008b,a; Hickox et al. 2009).”
Near infrared spectroscopy and star-formation histories of 3 ≤ z ≤ 4 quiescent galaxies (2018, background): “Nowadays, the most favored actor for quenching is the feedback that slow and fast-growing supermassive black holes can apply on their host galaxies (e.g., Silk & Rees 1998; Bower et al. 2006; Croton et al. 2006; Hopkins et al. 2008; Cattaneo et al. 2009).”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. II. “CUSP” ELLIPTICALS (2008, methodology): “…figure is available in the online journal.) the early-type or red galaxy mass functions (Bundy et al. 2006; Borch et al. 2006; Fontana et al. 2006; Hopkins et al. 2006c, 2008b), from direct stellar population synthesis studies (Trager et al. 2000; Thomas et al. 2005; Gallazzi et al. 2005), and by…”
PRIMUS: CONSTRAINTS ON STAR FORMATION QUENCHING AND GALAXY MERGING, AND THE EVOLUTION OF THE STELLAR MASS FUNCTION FROM z = 0–1 (2013, methodology): “By incorporating these quenching mechanisms into a coherent cosmological framework, modern theoretical models have become reasonably successful at reproducing a wide range of galaxy properties, including galaxy bimodality (e.g., Hopkins et al. 2008a,b; Somerville et al. 2008; Bower et al. 2012).”
Galaxies in a simulated ΛCDM universe – II. Observable properties and constraints on feedback (2009, methodology): “Using the halo occupation distribution and the evolution of a type-separated galaxy mass function, (Hopkins et al. 2008a,b) show that such a model, which assumes that star formation stops after the major mergers of gas-rich galaxies, can explain the buildup of the red sequence over time as well as…”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, methodology): “…L∗ ellipticals (in terms of their profile shapes, effective radii and fundamental plane correlations, rotation and higher-order kinematics, isophotal shapes, triaxiality, and other prope ties; see e.g. Naab et al. 2006; Cox et al. 2006a; Jesseit et al. 2007, 2009; Hopkins et al. 2008c,a, 2009c)23.”
He ii REIONIZATION AND ITS EFFECT ON THE INTERGALACTIC MEDIUM (2008, background): “…mass (Hopkins et al. 2007a,b), and the halo occupation model of Tinker et al. (2005); Conroy et al. (2006); Vale & Ostriker (2006) (for details, see Hopkins et al. (2008a)) to map from halo mass to stellar mass.15 Figure 1 show the luminosity function that this model generates (red, dashed…”