The Identification of Z-dropouts in Pan-STARRS1: Three Quasars at 6.5< z< 6.7

Venemans, B.P.; Bañados, E.; Decarli, R.; Farina, E.P.; Walter, F.; Chambers, K.C.; Fan, X.; Rix, H.-W.; Schlafly, E.; McMahon, R.G.; Simcoe, R.; Stern, D.; Burgett, W.S.; Draper, P.W.; Flewelling, H.; Hodapp, K.W.; Kaiser, N.; Magnier, E.A.; Metcalfe, N.; Morgan, J.S.; Price, P.A.; Tonry, J.L.; Waters, C.; AlSayyad, Y.; Banerji, M.; Chen, S.S.; González-Solares, E.A.; Greiner, J.; Mazzucchelli, C.; McGreer, I.; Miller, D.R.; Reed, S.; Sullivan, P.W.

Abstract

Luminous distant quasars are unique probes of the high-redshift intergalactic medium (IGM) and of the growth of massive galaxies and black holes in the early universe. Absorption due to neutral hydrogen in the IGM makes quasars beyond a redshift of $z\simeq 6.5$ very faint in the optical z band, thus locating quasars at higher redshifts requires large surveys that are sensitive above 1 micron. We report the discovery of three new $z\gt 6.5$ quasars, corresponding to an age of the universe of $\lt 850$ Myr, selected as z-band dropouts in the Pan-STARRS1 survey. This increases the number of known $z\gt 6.5$ quasars from four to seven. The quasars have redshifts of z = 6.50, 6.52, and 6.66, and include the brightest z-dropout quasar reported to date, PSO J036.5078 + 03.0498 with ${{M}_{1450}}=-27.4$. We obtained near-infrared spectroscopy for the quasars, and from the Mg ii line, we estimate that the central black holes have masses between 5 × 108 and 4 × 109 ${{M}_{\odot }}$ and are accreting close to the Eddington limit (${{L}_{{\rm Bol}}}/{{L}_{{\rm Edd}}}=0.13-1.2$). We investigate the ionized regions around the quasars and find near-zone radii of ${{R}_{{\rm NZ}}}=1.5-5.2$ proper Mpc, confirming the trend of decreasing near-zone sizes with increasing redshift found for quasars at $5.7\lt z\lt 6.4$. By combining RNZ of the PS1 quasars with those of $5.7\lt z\lt 7.1$ quasars in the literature, we derive a luminosity-corrected redshift evolution of ${{R}_{{\rm NZ},{\rm corrected}}}=(7.2\pm 0.2)-(6.1\pm 0.7)\times (z-6)$ Mpc. However, the large spread in RNZ in the new quasars implies a wide range in quasar ages and/or a large variation in the neutral hydrogen fraction along different lines of sight.

Citation

Venemans, B., Bañados, E., Decarli, R., Farina, E., Walter, F., Chambers, K., …Sullivan, P. (2015). The Identification of Z-dropouts in Pan-STARRS1: Three Quasars at 6.5< z< 6.7. Astrophysical Journal Letters, 801(1), Article L11. https://doi.org/10.1088/2041-8205/801/1/l11

• Journal Article Type: Article
• Acceptance Date: Feb 5, 2015
• Online Publication Date: Feb 27, 2015
• Publication Date: Mar 1, 2015
• Deposit Date: Jun 16, 2015
• Publicly Available Date: Jul 1, 2015
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 801
• Issue: 1
• Article Number: L11
• DOI: https://doi.org/10.1088/2041-8205/801/1/l11
• Keywords: Cosmology: observations, Galaxies: active, Galaxies: individual (PSO J036.5078+03.0498, PSO J167.6415-13.4960, PSO J338.2298+29.5089), Quasars: general.