Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

Abstract

We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M _*) in the CANDELS/GOODS-South field in the redshift range of 0.5≤slant z< 2.0. Our sample consists of ≈ {{18,000}} galaxies, allowing us to probe galaxies with 0.1{M}_⊙ {{yr}}^-1≲ {SFR}≲ 100 {M}_⊙ {{yr}}^-1 and/or {10}⁸{M}_⊙ ≲ {M}_* ≲ {10}¹¹ {M}_⊙ . We use sample-mean BHAR to approximate long-term average BHAR. Our sample-mean BHARs are derived from the Chandra Deep Field-South 7 Ms observations, while the SFRs and M _* have been estimated by the CANDELS team through spectral energy distribution fitting. 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, BHAR appears to be correlated more strongly with M _* than SFR. This result indicates that M _* is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ({M}_* ≳ {10}¹⁰{M}_⊙ ) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between {M}_{BH} and M _* for local giant ellipticals and suggest that their {M}_{BH}/{M}_* is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher {M}_{BH}/{M}_* compared to dwarfs.