A Survey of [CLC][ITAL]z[/ITAL][/CLC] ] 5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at [CLC][ITAL]z[/ITAL][/CLC] ] 6

Abstract

We present the discovery of three new quasars at z > 6 in $ 1300 deg 2 of Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z = 6.43), J104845.05+463718.3 (z = 6.23), and J163033.90+401209.6 (z = 6.05). The first two objects have weak Ly emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to $0.05 and could be affected by the presence of broad absorption line systems. The last object has a Ly strength more typical of lower redshift quasars. Based on a sample of six quasars at z > 5.7 that cover 2870 deg 2 presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z $ 6 and M 1450 < À26.8 to be (8 AE 3) Â 10 À10 Mpc À3 (for H 0 = 50 km s À1 Mpc À1 , = 1). Hubble Space Telescope imaging of two z > 5.7 quasars and high-resolution, ground-based images (seeing $0>4) of three additional z > 5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshift quasar sample suggests the bright-end slope of the quasar luminosity function at z $ 6 is shallower than É / L À3.5 (2 ), consistent with the absence of strongly lensed objects.

Overview of EXIST mission science and implementation

“…1a). GRB080913 (z = 6.7) 4 and GRB090423 (z = 8.2) 5,6 both exceed the highest redshift quasar (z = 6.43) discovered 7 with the Sloan Digital Sky Survey. GRBs are thus the most distant as well as bright beacons with which to study the early Universe.…”

Evolution of supermassive black holes

“…It could be shown that the most massive SMBH with billions of solar masses were already in place at z ≃ 3. Indeed, this is observed for some SDSS quasars (Fan et al 2003). Merloni (2004) has also demonstrated that radiatively inefficient accretion (e.g.…”

A Practical Guide to the Massive Black Hole Cosmic History

“…Note that these systems have a space density of 1 Gpc −3 comoving volume [2], corresponding to 5σ fluctuations of the original density field [96]. This means that they are not representative of the typical MBH cosmic evolution; they are extremely rare and grew in the richest overdensities of the early Universe.…”

“…Observations of quasars out to redshift º7 [1][2][3] imply that some of these objects were already in place when the Universe was less than a billion year old, although the bulk of quasar population in the Universe comes later, at z ≈ 2 [4]. In the last twenty years, evidence for the existence of MBHs has also been found in nearby quiescent galaxies.…”