Optical identification of serendipitous Einstein X-ray sources - Luminosity and redshift relations in the X-ray and optical emission from active galaxies and quasars

Abstract

view Abstract Citations (82) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical identification of serendipitous Einstein sources : luminosity and redshift relations in the X-ray and optical emission from active galaxies and quasars. Reichert, G. A. ; Mason, K. O. ; Thorstensen, J. R. ; Bowyer, S. Abstract We have optically identified 40 objects from a sample of 139 serendipitous Einstein X-ray sources. Thirteen of the sources are identified with galactic counterparts, and 27 are identified with extragalactic counterparts. The galactic counterparts include normal bright (V< 10) stars, emission line stars, RS CVn stars, and cataclysmic variables; these are similar in their X-ray properties to other galactic objects observed at X-ray wavelengths. All but one of the extragalactic counterparts are active galactic nuclei (AGNs). The optical spectra of the X-ray selected AGNs are indistinguishable from those of AGNs discovered by their radio or optical emission. We have combined our sample of X-ray selected AGNs with other samples of X-ray selected and previously cataloged AGNs in order to investigate correlations between their optical and X-ray properties. No significant correlations between emission line luminosities and X-ray luminosity are found, when the separate correlations with optical luminosity are taken into account. Previously reported correlations of the ratio of the luminosities in Hβ and in [O III], and of the widths of the Hβ emission lines, with continuum luminosities are shown to be artifacts due to systematic differences between narrow line and broad line objects. The ratio of X-ray luminosity to optical luminosity is observed to decrease with increasing optical luminosity. Regression analysis shows that Lx/L0 cannot be constant, but must decrease by at least a factor of 1.6 for every factor 10 increase in L0, and may decrease by more if Lx/L0 also increases with increasing redshift. The data do not allow Lx/L0 to decrease with increasing redshift. The observed variation in Lx/L0 with L0 is sufficient to explain the deficit of intermediate and high redshift (z > 0.5) AGNs in the X-ray selected sample, and it is therefore not necessary to propose constraints on the luminosity evolution of AGNs, or systematic differences in X-ray emission between X-ray selected and optically selected AGNs. The expected contribution to the extragalactic X-ray background from AGNs depends critically upon the assumed relationship between Lx and L0, ranging (for objects brighter than B=20) from 20% of the observed background for weak variation in Lx/L0 to 50% for a strong variation in Lx/L0. Publication: The Astrophysical Journal Pub Date: September 1982 DOI: 10.1086/160267 Bibcode: 1982ApJ...260..437R Keywords: Active Galaxies; Astronomical Spectroscopy; Galactic Nuclei; Optical Emission Spectroscopy; Quasars; Red Shift; X Ray Sources; Binary Stars; Emission Spectra; Extraterrestrial Radiation; Graphs (Charts); Light Emission; Line Spectra; Spectral Line Width; Stellar Luminosity; Astronomy full text sources ADS | data products NED (36) SIMBAD (1)