2007/02/02 by Sumin Tang, S. M. Tang, Shuang‐Nan Zhang +2 · 2 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2007.11589.x
published as Mon.Not.Roy.Astron.Soc.377:1113-1121,2007 · 10 pages, 11 figures, accepted for publication in MNRAS
arxiv created 2007/02/02 · openalex publication_date 2007/05/06 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
We critically examine the dependence of spectral index on luminosity in optically selected AGN samples. An analysis of optically selected high-z quasars showed an anticorrelation of αOX, the spectral index between the rest-frame 2500 Å and 2 keV, with optical luminosity. We examine this relationship by means of Monte Carlo simulations and conclude that a constant αOX independent of optical luminosity is still consistent with this high-z sample. We further find that contributions of large dispersions and narrow range of optical luminosity are most important for the apparent, yet artificial, αOX–lo correlation reported. We also examine another, but more complete, low-z optical selected AGN sub-sample from Steffen et al., and our analysis shows that a constant αOX independent of optical luminosity is also consistent with the data. By comparing X-ray and optical luminosity functions, we find that a luminosity-independent αOX is in fact more preferred than the luminosity-dependent αOX model. We also discuss the selection effects caused by flux limits, which might systematically bias the lX–lo relation and cause discrepancy in optically selected and X-ray selected AGN samples. To correctly establish a dependence of αOX of AGNs on their luminosity, a larger and more complete sample is needed and consequences of luminosity dispersions and selection effects in flux-limited samples must be taken into account properly.