IR to X-ray spectral energy distributions of high redshift quasars

AIP conference proceedings1994Vol. 313, pp. 105–109

Jill Bechtold, R. M. Cutri, Marcia Rieke, M. Elvis, F. Fiore, B. J. Wilkes, Jonathan McDowell, Aneta Siemignowska

Abstract

We have observed 13 quasars having z≳2.8 with the ROSAT PSPC, and detected 12 of them, including the z=4.11 quasar 0000–263. For the radio quiet quasars with z≳2.5, the mean 〈αox〉∼1.8. Thus, the high redshift quasars are relatively more X‐ray quiet than quasars with z<2.5. However given their high optical luminosities, they are consistent with the extrapolation of the dependence of 〈αox〉 on 1opt seen at low redshift. For the radio‐loud quasars, 〈αox〉∼1.4, independent of redshift. This is smaller than the expected value for the optically luminous, high redshift objects, if they are comparable to steep‐spectrum, compact radio sources at low redshift. For 6 of the quasars, there are sufficient counts detected to provide meaningful constraints to the X‐ray spectrum. For the others, a PSPC hardness ratio is used to constrain the X‐ray spectral properties. The observations imply that at z≊3, the X‐ray spectra of radio‐loud and radio‐quiet quasars are different. Implications for the interpretation of the evolution of the luminosity function of quasars are discussed. Models where quasars are numerous and short‐lived are favored.

Abstract

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