Investigating the Star Formation Rates of AGN Hosts Relative to the Star-Forming Main Sequence

A fundamental question in galaxy and black-hole evolution remains how galaxies and their supermassive black holes have evolved together over cosmic time. Specifically, it is still unclear how the position of X-ray active galactic nucleus (AGN) host galaxies with respect to the star-forming main sequence (MS) may change with the X-ray luminosity (L_X) of the AGN or the stellar mass (M_⋆) of the host galaxy. We use data from XMM-SERVS to probe this issue. XMM-SERVS is covered by the largest medium-depth X-ray survey (with superb supporting multiwavelength data) and thus contains the largest sample to date for study. To ensure consistency, we locally derive the MS from a large reference galaxy sample. In our analysis, we demonstrate that the turnover of the galaxy MS does not allow reliable conclusions to be drawn for high-mass AGNs, and we establish a robust safe regime where the results do not depend upon the choice of MS definition. Under this framework, our results indicate that less-massive AGN host-galaxies (log M_⋆∼9.5-10.5 M_⊙) generally possess enhanced SFRs compared to their normal-galaxy counterparts while the more-massive AGN host galaxies (log M_⋆∼10.5-11.5 M_⊙) lie on or below the star-forming MS. Further, we propose an empirical model for how the placement of an AGN with respect to the MS (SFR_norm) evolves as a function of both M_⋆ and L_X.