Desde Diciembre 11, 2017 15:30 hasta Diciembre 11, 2017 16:00
En Seminar Room
The Chandra exposure on the Chandra Deep Field-South (CDF-S) has recently been increased to 7 Ms, allowing unmatched X-ray and multiwavelength characterization of cosmic black-hole growth in active galactic nuclei (AGNs). We have used these data to investigate the dependence of black-hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M*) at z = 0.5-2. Our sample consists of 18,000 galaxies with SFR and M* measurements, and we use sample-mean BHAR for these galaxies to approximate their long-term average BHAR. Our sample-mean BHARs are derived from the CDF-S observations via both direct spectral analysis and stacking. The average BHAR is correlated positively with both SFR and M*, and the BHAR-SFR and BHAR-M* relations can both be described acceptably by linear models with a slope of unity. However, according to partial-correlation analyses, BHAR is correlated more strongly with M* than SFR. This result indicates that M* is the primary (observable) host-galaxy property related to black-hole growth, and the well-known BHAR-SFR relation is largely a secondary effect due to the "star-forming main sequence". We have also recently extended this work over z = 0.5-4 by combining data from the CDF-S, CDF-N, and COSMOS (as well as the X-ray luminosity function). These extended analyses clearly show that massive galaxies have significantly higher BHAR/SFR ratios than less-massive galaxies, indicating the former have higher black-hole fueling efficiency and/or higher SMBH occupation fraction than the latter; e.g., the deeper potential wells in higher mass galaxies may promote black-hole accretion and counteract AGN/supernova feedback. Our results predict the average M_BH/M* ratio should increase with M*, ranging between 1/5000 at low M* and 1/500 at high M*. Finally, prospects for extending this work will be discussed.