THE HALO MASSES AND GALAXY ENVIRONMENTS OF HYPERLUMINOUS QSOs AT z ≃ 2.7 IN THE KECK BARYONIC STRUCTURE SURVEY

We present an analysis of the galaxy distribution surrounding 15 of the most luminous (greater than or similar to 10(14) L-circle dot; M-1450 similar or equal to -30) QSOs in the sky with z similar or equal to 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 similar to 2-3. In this work, we use the positions and spectroscopic redshifts of 1558 galaxies that lie within similar to 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 sigma(upsilon) similar or equal to 200 km s(-1) and a transverse angular scale of similar to 25 '' (similar to 200 physical kpc). We argue that such scales are expected for small groups with log(M-h/M-circle dot) similar or equal to 13. The galaxy-HLQSO cross-correlation function has a best-fit correlation length r(0)(GQ) = (7.3 +/- 1.3) h(-1) cMpc, while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r(0)(GG) = (6.0 +/- 0.5) h(-1) cMpc. Based on a comparison with simulations evaluated at z similar to 2.6, these values imply that a typical galaxy lives in a host halo with log(M-h/M-circle dot) = 11.9 +/- 0.1, while HLQSOs inhabit host halos of log(M-h/M-circle dot) = 12.3 +/- 0.5. In spite of the extremely large black hole masses implied by their observed luminosities [log(M-BH/M-circle dot) greater than or similar to 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 (less than or similar to 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.