The X-Ray-to-Optical Properties of Optically Selected Active Galaxies over Wide Luminosity and Redshift Ranges

We present partial-correlation analyses that examine the strengths of therelationships between L_UV, L_X, Alpha_OX, and redshift for optically-selectedAGNs. We extend the work of Strateva et al. (2005), that analyzedoptically-selected AGNs from the Sloan Digital Sky Survey (SDSS), by including52 moderate-luminosity, optically-selected AGNs from the COMBO-17 survey withcorresponding deep (~250 ks to 1 Ms) X-ray observations from the ExtendedChandra Deep Field-South. The COMBO-17 survey extends ~3 magnitudes deeper thanthe SDSS and probes the moderate-luminosity AGNs that numerically dominate theAGN population in the Universe. We also include recently published observationsof 19 high-redshift, optically-selected AGNs, and 46 luminous, low-redshiftAGNs from the Bright Quasar Survey. The full sample used in our analysisconsists of 333 AGNs, extending out to z~6, with 293 (88%) having X-raydetections. The sample spans five decades in UV luminosity and four decades inX-ray luminosity. We confirm that Alpha_OX is strongly anti-correlated withL_UV (13.6 sigma), the highest significance found for this relation to date,and find evidence suggesting that the slope of this relation may be dependenton L_UV. We find that no significant correlation exists between Alpha_OX andredshift (1.3 sigma), and constrain the maximum evolution of AGN UV-to-X-rayflux ratios to be less than 30% (1 sigma) out to z=5. Using our sample's highX-ray detection fraction, we also find a significant anti-correlation (3.0sigma) between Alpha_OX and L_X . We make comparisons to earlier studies onthis topic and discuss implications for X-ray vs. optical luminosity functions.Comment: 16 pages, 10 figures, emulateapj. Accepted for publication in A