Chien-Ting Chen (ST12) is co-author on an article recently published in The Astrophysical Journal, "Consistent Analysis of the AGN LF in X-Ray and MIR in the XMM-LSS Field".
The luminosity function (LF) of active galactic nuclei (AGN) probes the history of supermassive black hole (SMBH) assembly and growth across cosmic time. A complete view of the AGN population requires both X-ray and mid-infrared (MIR) observations since a substantial fraction of SMBH accretion is dust obscured. The paper presents a consistent analysis of the AGN luminosity functions (LFs) derived for both X-ray and MIR selected AGN in the XMM-Large Scale Structure field, which is among one of the most extensively targeted sky region, including the Great Observatories, and it is one of the planned deep-drilling survey fields of the upcoming Rubin Observatory.
There are 4268 AGN used to construct the MIR luminosity function (IRLF) and 3427 AGN used to construct the X-ray luminosity function (XLF), providing the largest census of the AGN population out to z = 4 in both bands with significant reduction in uncertainties. We are able for the first time to see the knee of the IRLF at z > 2 and observe a flattening of the faint-end slope as redshift increases. The bolometric luminosity density, a proxy for the cosmic black hole accretion history, computed from our LFs, shows a peak at z ~ 2.25, consistent with recent estimates of the peak in the star formation rate density (SFRD). However, at earlier epochs, the AGN luminosity density is flatter than the SFRD. If confirmed, this result suggests that the buildup of black hole mass outpaces the growth of stellar mass in high-mass systems at z ≳ 2.5. This is consistent with observations of redshift z ~ 6 quasars that lie above the local BH mass-galactic bulge velocity dispersion relationship. The luminosity density derived from the IRLF is higher than that from the XLF at all redshifts. This is consistent with the dominant role of obscured AGN activity in the cosmic growth of supermassive black holes.
The published paper is available at https://iopscience.iop.org/article/10.3847/1538-4357/ac37b8
Postage stamps of VIDEO K-band sources (top of each row) and the corresponding XMM-SERVS X-ray sources (bottom of each row) that contribute to the uptick in the XLF at low redshifts and high luminosities.
