We compare the set of local galaxies having dynamically measured black holes with a large, unbiased sample of galaxies extracted from the Sloan Digital Sky Survey. We confirm earlier work showing that the majority of black hole hosts have significantly higher velocity dispersions ? than local galaxies of similar stellar mass. We use Monte Carlo simulations to illustrate the effect on black hole scaling relations if this bias arises from the requirement that the black hole sphere of influence must be resolved to measure black hole masses with spatially resolved kinematics. We find that this selection effect artificially increases the normalization of the Mbh–? relation by a factor of at least ?3; the bias for the Mbh–Mstar relation is even larger. Our Monte Carlo simulations and analysis of the residuals from scaling relations both indicate that ? is more fundamental than Mstar or effective radius. In particular, the Mbh–Mstar relation is mostly a consequence of the Mbh–? and ?–Mstar relations, and is heavily biased by up to a factor of 50 at small masses. This helps resolve the discrepancy between dynamically based black hole–galaxy scaling relations versus those of active galaxies. Our simulations also disfavour broad distributions of black hole masses at fixed ?. Correcting for this bias suggests that the calibration factor used to estimate black hole masses in active galaxies should be reduced to values of fvir ? 1. Black hole mass densities should also be proportionally smaller, perhaps implying significantly higher radiative efficiencies/black hole spins. Reducing black hole masses also reduces the gravitational wave signal expected from black hole mergers.

Selection bias in dynamically measured supermassive black hole samples: its consequences and the quest for the most fundamental relation

According to modern theory, galactic evolution is driven by the dynamics of dark matter and stochastic star formation, but galaxies are observed to be simple systems. The existence of dark matter p...

Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation

U.S. National Science Foundation [AST-1440226, AST-0965625, AST-0408698]; Princeton University; University of Pennsylvania; Canada Foundation for Innovation (CFI); Comision Nacional de Investigacion Cientifica y Tecnologica de Chile (CONICYT); CFI under Compute Canada; Government of Ontario; Ontario Research Fund-Research Excellence; University of Toronto; NASA [NNX13AE56G, NNX14AB58G, NNX14AF73G, ATP NNX14AB57G]; National Research Foundation; South African Square Kilometre Array project; University of KwaZulu-Natal; Lyman Spitzer Jr. Fellowship; NSF [AST-1615657, AST-1312991, AST-1312380]; ERC [259505, 267117]; Labex ILP part of the Idex SUPER [ANR-10-LABX-63]; DOE [DE-SC0011114]; NASA Space Technology Research Fellowships; CONICYT [FONDECYT 1141113, Anillo ACT-1417, QUIMAL 160009, BASAL PFB-06 CATA]; CONICYT FONDECYT [3170846]; Jet Propulsion Laboratory, California Institute of Technology; National Aeronautics and Space Administration; Mishrahi Fund; Wilkinson Fund; Rutgers University; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; FIRST program from the Japanese Cabinet Office; Ministry of Education, Culture, Sports, Science and Technology (MEXT); Japan Society for the Promotion of Science (JSPS); Japan Science and Technology Agency (JST); Toray Science Foundation; NAOJ; Kavli IPMU; KEK; ASIAA; National Aeronautics and Space Administration [NNX08AR22G]; National Science Foundation [AST-1238877]; ESO Very Large Telescope, under the "Large Programme" [182.A-0886]; [PHY-1214379]; [PHY-0855887]; [ANR-11-IDEX-0004-02]

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The Atacama Cosmology Telescope: The Two-season ACTPol Sunyaev–Zel’dovich Effect Selected Cluster Catalog

We present a catalog of 182 galaxy clusters detected through the Sunyaev-Zel'dovich effect by the Atacama Cosmology Telescope in a contiguous 987.5 deg$^{2}$ field. The clusters were detected as SZ decrements by applying a matched filter to 148 GHz maps that combine the original ACT equatorial survey with data from the first two observing seasons using the ACTPol receiver. Optical/IR confirmation and redshift measurements come from a combination of large public surveys and our own follow-up observations. Where necessary, we measured photometric redshifts for clusters using a pipeline that achieves accuracy $\Delta z/(1 + z)=0.015$ when tested on SDSS data. Under the assumption that clusters can be described by the so-called Universal Pressure Profile and its associated mass-scaling law, the full signal-to-noise > 4 sample spans the mass range $1.6 4 \times 10^{14}$ M$_{\odot}$ is consistent with the number of such clusters found in the South Pole Telescope SZ survey.

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The Atacama Cosmology Telescope: The Two-Season ACTPol Sunyaev-Zel'dovich Effect Selected Cluster Catalog

We present an analysis of galaxies in groups and clusters at 0.8 1010.3 M⊙, we find fconvert ∼ 0.4 in the groups and ∼0.6 in the clusters, similar to comparable measurements at z = 0. This means the time between first accretion into a more massive halo and final star formation quenching is tp ∼ 2 Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay time-scale may depend on stellar mass, with tp approaching tHubble for Mstar ∼ 109.5 M⊙. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to ‘overconsumption’, the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at z = 1.

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Evidence for a change in the dominant satellite galaxy quenching mechanism at z = 1.

Recent independent results from numerical simulations and observations have shown that brightest cluster galaxies (BCGs) have increased their stellar mass by a factor of almost 2 between z ∼ 0.9 and z ∼ 0.2. The numerical simulations further suggest that more than half this mass is accreted through major mergers. Using a sample of 18 distant galaxy clusters with over 600 spectroscopically confirmed cluster members between them, we search for observational evidence that major mergers do play a significant role. We find a major merger rate of 0.38 ± 0.14 mergers per Gyr at z ∼ 1. While the uncertainties, which stem from the small size of our sample, are relatively large, our rate is consistent with the results that are derived from numerical simulations. If we assume that this rate continues to the present day and that half of the mass of the companion is accreted on to the BCG during these mergers, then we find that this rate can explain the growth in the stellar mass of the BCGs that is observed and predicted by simulations. Major mergers therefore appear to be playing an important role, perhaps even the dominant one, in the build up of stellar mass in these extraordinary galaxies.

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The Importance of Major Mergers in the Build Up of Stellar Mass in Brightest Cluster Galaxies at z = 1

We compare state-of-the-art semi-analytic models of galaxy formation as well as advanced subhalo abundance matching models with a large sample of early-type galaxies from Sloan Digital Sky Survey at z < 0.3. We focus our attention on the dependence of median sizes of central galaxies on host halo mass. The data do not show any difference in the structural properties of early-type galaxies with environment, at fixed stellar mass. All hierarchical models considered in this work instead tend to predict a moderate to strong environmental dependence, with the median size increasing by a factor of ?1.5–3 when moving from low- to high-mass host haloes. At face value the discrepancy with the data is highly significant, especially at the cluster scale, for haloes above log?Mhalo ? 14. The convolution with (correlated) observational errors reduces some of the tension. Despite the observational uncertainties, the data tend to disfavour hierarchical models characterized by a relevant contribution of disc instabilities to the formation of spheroids, strong gas dissipation in (major) mergers, short dynamical friction time-scales and very short quenching time-scales in infalling satellites. We also discuss a variety of additional related issues, such as the slope and scatter in the local size–stellar mass relation, the fraction of gas in local early-type galaxies and the general predictions on satellite galaxies.

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L. Delaye

Papers

The Importance of Major Mergers in the Build Up of Stellar Mass in Brightest Cluster Galaxies at z = 1

Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe