1305.3917 (M. Brightman et al.)

A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys    [PDF]

M. Brightman, J. D. Silverman, V. Mainieri, Y. Ueda, M. Schramm, K. Matsuoka, T. Nagao, C. Steinhardt, J. Kartaltepe, D. B. Sanders, E. Treister, O. Shemmer, W. N. Brandt, M. Brusa, A. Comastri, L. C. Ho, G. Lanzuisi, E. Lusso, K. Nandra, M. Salvato, G. Zamorani, M. Akiyama, D. M. Alexander, A. Bongiorno, P. Capak, F. Civano, A. Del Moro, A. Doi, M. Elvis, G. Hasinger, E. S. Laird, D. Masters, M. Mignoli, K. Ohta, K. Schawinski, Y. Taniguchi

We present an investigation into how well the properties of the accretion flow onto a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, Gamma, of a power-law energy distribution, over an energy range of 2 to 10 keV, for X-ray selected, broad-lined radio-quiet AGN up to z~2 in COSMOS and E-CDF-S. We test the previously reported dependence between Gamma and black hole mass, FWHM and Eddington ratio using a sample of AGN covering a broad range in these parameters based on both the Mg ii and H-alpha emission lines with the later afforded by recent near infrared spectroscopic observations using Subaru/FMOS. We calculate the Eddington ratios, lambda_Edd, for sources where a bolometric luminosity (L_Bol) has been presented in the literature, based on SED fitting, or, for sources where these data do not exist, we calculate L_Bol using a bolometric correction to the LX, derived from a relationship between the bolometric correction, and LX/L3000. From a sample of 69 X-ray bright sources (>250 counts), where Gamma can be measured with greatest precision, with an estimate of L_Bol, we find a statistically significant correlation between Gamma and lambda_Edd, which is highly significant with a chance probability of 6.59x10^-8. A statistically significant correlation between Gamma and the FWHM of the optical lines is confirmed, but at lower significance than with lambda_Edd indicating that lambda_Edd is the key parameter driving conditions in the corona. Linear regression analysis reveals that Gamma=(0.32+/-0.05)log10 lambda_Edd+(2.27+/-0.06) and Gamma=(-0.69+/-0.11)log10(FWHM/km/s)+(4.44+/-0.42). Our results on Gamma-lambda_Edd are in very good agreement with previous results. (ABRIDGED)

View original: http://arxiv.org/abs/1305.3917