The X-Ray Properties of z > 4 Quasars

We report on a search for X-ray emission from quasars with redshifts greater than 4 using the ROSAT public database. Our search has doubled the number of z > 4 quasars detected in X-rays from six to 12. Most of those known prior to this work were radio-loud and X-ray–selected sources; our study increases the number of X-ray–detected, optically selected z > 4 quasars from one to seven. We present their basic X-ray properties and compare these with those of lower redshift quasars. We do not find any evidence for strong broadband spectral differences between optically selected z > 4 quasars and those at lower redshifts.

[1]  R. McMahon,et al.  Submillimetre observations of luminous z>4 radio-quiet quasars and the contribution of AGN to the submm source population , 1999, astro-ph/9907239.

[2]  Cambridge,et al.  Variability of the extreme z = 4.72 blazar, GB 1428+4217 , 1999, astro-ph/9907033.

[3]  W. N. Brandt,et al.  On the Nature of Soft X-Ray Weak Quasi-stellar Objects , 1999, astro-ph/9908016.

[4]  D. Schneider.  Surveys for high-redshift quasars , 1999 .

[5]  E. O. Smith,et al.  After the dark ages : when galaxies were young (the universe at 2 < z < 5) : ninth astrophysics conference, College Park, Maryland October 1998 , 1999 .

[6]  R. Nichol,et al.  High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data , 1999, astro-ph/0103228.

[7]  D. Schneider,et al.  Discovery of an X-Ray-selected Quasar with a Redshift of 4.45 , 1998 .

[8]  I. Hook,et al.  The ASCA spectrum of the z=4.72 blazar GB 1428+4217. , 1998, astro-ph/9801288.

[9]  I. Hook,et al.  Discovery of radio‐loud quasars with z=4.72 and z=4.010 , 1998, astro-ph/9801026.

[10]  P. Giommi,et al.  X-Ray Spectral Survey of WGACAT Quasars. II. Optical and Radio Properties of Quasars with Low-Energy X-Ray Cutoffs , 1997, astro-ph/9708050.

[11]  P. Giommi,et al.  X-Ray Spectral Survey of WGACAT Quasars. I. Spectral Evolution and Low-Energy Cutoffs , 1997, astro-ph/9708049.

[12]  B. Boyle,et al.  QSO X-ray spectral evolution , 1998 .

[13]  T. Kii,et al.  AN X-RAY SURVEY OF QUASARS USING ASCA , 1997 .

[14]  B. Boyle,et al.  Faint galaxies and the X-ray background , 1997, astro-ph/9711150.

[15]  I. Hook,et al.  The extreme X-ray luminosity of the z = 4.72 radio-loud quasar GB 1428+4217 , 1997 .

[16]  M. Hawkins,et al.  THE SPACE DENSITY OF QUASARS AT Z > 4 , 1996 .

[17]  M. Irwin,et al.  APM z>4 QSO Survey: Spectra and Intervening Absorption Systems , 1996, astro-ph/9604021.

[18]  R. Becker,et al.  The Einstein Two-Sigma Catalog: Silver Needles in the X-Ray Haystack , 1996 .

[19]  E. Physik.  RONTGENSTRAHLUNG FROM THE UNIVERSE , 1996 .

[20]  K. Kellermann,et al.  PKS 1251 - 407: a radio-loud quasar at z = 4.46 , 1996 .

[21]  S. Mathur,et al.  GB 1508+5714, The First z>4 Radio-Selected Quasar in X-Rays , 1995 .

[22]  P. Hewett,et al.  The Soft X-Ray Properties of a Large Optical QSO Sample: ROSAT Observations of the Large Bright Quasar Survey , 1995 .

[23]  Richard L. White,et al.  The FIRST Survey: Faint Images of the Radio Sky at twenty centimeters , 1995 .

[24]  J. Gunn,et al.  Differential evolution of radio quiet and radio loud quasars , 1995 .

[25]  E. Greisen,et al.  The NRAO VLA Sky Survey , 1996 .

[26]  M. Rieke,et al.  X-ray spectral evolution of high redshift quasars , 1994 .

[27]  M. Rieke,et al.  Infrared to x-ray spectral energy distributions of high redshift quasars , 1994 .

[28]  A. Fabian.  Hot plasmas and the generation of gamma rays , 1994 .

[29]  M. S. Oey,et al.  THE EINSTEIN DATABASE OF IPC X-RAY OBSERVATIONS OF OPTICALLY SELECTED AND RADIO-SELECTED QUASARS .1. , 1994 .

[30]  R. Ellis,et al.  RX J1759.4+6638: an x-ray selected quasar at a redshift of 4.320 , 1994 .

[31]  R. McMahon,et al.  1.25-mm continuum observations of very high-redshift QSOs:is there dust at Z = 4.69? , 1994 .

[32]  E. Feigelson,et al.  PUBLIC SOFTWARE FOR THE ASTRONOMER: AN OVERVIEW , 1992 .

[33]  J. Gunn,et al.  Radio properties of optically selected high-redshift quasars. I - VLA observations of 22 quasars at 6 cm , 1992 .

[34]  D. Schneider,et al.  Moderate resolution spectrophotometry of high redshift quasars , 1991 .

[35]  M. Mayor,et al.  Active Galactic Nuclei: Saas-Fee Advanced Course 20. Lecture Notes 1990. Swiss Society for Astrophysics and Astronomy , 1991 .

[36]  E. Turner.  Quasars and galaxy formation. I - The z greater than 4 objects , 1991 .

[37]  J. Dickey,et al.  H I in the Galaxy , 1990 .

[38]  H. Netzer.  AGN Emission Lines , 1990 .

[39]  J. Gunn,et al.  A study of ten quasars with redshifts greater than four , 1989 .

[40]  Maarten Schmidt,et al.  VLA observations of objects in the Palomar Bright Quasar Survey , 1989 .

[41]  M. Irwin,et al.  First observation of a quasar with a redshift of 4 , 1987, Nature.

[42]  Elmar Pfeffermann,et al.  The Focal Plane Instrumentation Of The ROSAT Telescope , 1986, Other Conferences.

[43]  P. I. Nelson,et al.  Statistical methods for astronomical data with upper limits. II - Correlation and regression , 1986 .

[44]  P. I. Nelson,et al.  Statistical methods for astronomical data with upper limits. I - Univariate distributions , 1985 .