The identification of z-dropouts in pan-starrs1: Three quasars at 6.5< z< 6.7

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

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94 Scopus citations


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 ≃ 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 > 6.5 quasars, corresponding to an age of the universe of <850 Myr, selected as z-band dropouts in the Pan- STARRS1 survey. This increases the number of known z > 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 M1450 = -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⊙ and are accreting close to the Eddington limit (LBol LEdd = 0.13 - 1.2). We investigate the ionized regions around the quasars and find near-zone radii of RNZ = 1.5 - 5.2 proper Mpc, confirming the trend of decreasing near-zone sizes with increasing redshift found for quasars at 5.7 < z < 6.4. By combining RNZ of the PS1 quasars with those of 5.7 < z < 7.1 quasars in the literature, we derive a luminosity-corrected redshift evolution of RNZ,corrected = (7.2 ± 0.2) - (6.1 ± 0.7) × (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.

Original languageEnglish (US)
Article numberL11
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Mar 1 2015


  • cosmology: observations
  • galaxies: active
  • galaxies: individual (PSO J036.5078+03.0498, PSO J167.6415-13.4960, PSO J338.2298+29.5089)
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    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., ... Sullivan, P. W. (2015). The identification of z-dropouts in pan-starrs1: Three quasars at 6.5< z< 6.7. Astrophysical Journal Letters, 801(1), [L11].