The Halo Masses and Galaxy Environments of Hyperluminous QSOs at z ≃ 2.7 in the Keck Baryonic Structure Survey

Creators: Trainor, Ryan F.; Steidel, Charles C.

Abstract

We present an analysis of the galaxy distribution surrounding 15 of the most luminous (≳10^(14) L_☉; M_1450 ≃ –30) QSOs in the sky with z ≃ 2.7. Our data are drawn from the Keck Baryonic Structure Survey, which has been optimized to examine the small-scale interplay between galaxies and the intergalactic medium during the peak of the galaxy formation era at z ~ 2-3. In this work, we use the positions and spectroscopic redshifts of 1558 galaxies that lie within ~3' (4.2 h^(–1) comoving Mpc; cMpc) of the hyperluminous QSO (HLQSO) sight line in 1 of 15 independent survey fields, together with new measurements of the HLQSO systemic redshifts. By combining the spatial and redshift distributions, we measure the galaxy-HLQSO cross-correlation function, the galaxy-galaxy autocorrelation function, and the characteristic scale of galaxy overdensities surrounding the sites of exceedingly rare, extremely rapid, black hole accretion. On average, the HLQSOs lie within significant galaxy overdensities, characterized by a velocity dispersion σ_v ≃ 200 km s^(–1) and a transverse angular scale of ~25" (~200 physical kpc). We argue that such scales are expected for small groups with log (M _(h_/M_☉) ≃ 13. The galaxy-HLQSO cross-correlation function has a best-fit correlation length r^(GQ)_0 = (7.3 ± 1.3) h^(–1) cMpc, while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r^(GG)_0 = (6.0 ± 0.5) h^(–1) cMpc. Based on a comparison with simulations evaluated at z ~ 2.6, these values imply that a typical galaxy lives in a host halo with log (M_(h)/M_☉) = 11.9 ± 0.1, while HLQSOs inhabit host halos of log (M_(h)/M_☉) = 12.3 ± 0.5. In spite of the extremely large black hole masses implied by their observed luminosities [log (M_(BH)/M_☉) ≳ 9.7], it appears that HLQSOs do not require environments very different from their much less luminous QSO counterparts. Evidently, the exceedingly low space density of HLQSOs (≲ 10^(–9) cMpc^(–3)) results from a one-in-a-million event on scales ≪1 Mpc, and not from being hosted by rare dark matter halos.

Additional Information

© 2012 American Astronomical Society. Received 2011 October 14; accepted 2012 April 8; published 2012 May 23. We thank our collaborators for their important contributions to the Keck Baryonic Structure Survey over the course of many years: M. Bogosavljevic, D. Erb, D. R. Law, M. Pettini, O. Rakic, N. Reddy, G. Rudie, and A. Shapley. We also thank C. Bilinski for his help reducing some of the TripleSpec QSO spectra. R.F.T. also thanks B. Siana, N. Konidaris, A. Benson, C. Hirata, R. Quadri, and J. R. Gauthier for many useful discussions. We are grateful for the many useful comments we received from an anonymous referee, particularly in regard to the estimation of uncertainties in the correlation function parameters. The MultiDark Database used in this paper and the web application providing online access to it were constructed as part of the activities of the German Astrophysical Virtual Observatory as result of a collaboration between the Leibniz-Institute for Astrophysics Potsdam (AIP) and the Spanish MultiDark Consolider Project CSD2009-00064. The MultiDark simulation was run on NASA's Pleiades supercomputer at the NASA Ames Research Center. The Millennium Simulation databases used in this paper and the web application providing online access to them were constructed as part of the activities of the German Astrophysical Virtual Observatory. We are indebted to the staff of the W.M. Keck Observatory who keep the instruments and telescopes running effectively. We also wish to extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. This work has been supported by the US National Science Foundation through grants AST-0606912 and AST-0908805. C.C.S. acknowledges additional support from the John D. and Catherine T. MacArthur Foundation and the Peter and Patricia Gruber Foundation. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

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