High-Redshift AGN Reverberation Mapping and Variability with Roman

High-Redshift AGN Reverberation Mapping and Variability with Roman

Program ID	19090
Science Category	Active Galaxies & Supermassive Black Holes
Program Type	Analysis
Category	Small
Principal Investigator	Zachary Stone
PI Institution	University of Illinois, Urbana-Champaign
Co-Investigators	Yue Shen (University of Illinois, Urbana-Champaign)
Abstract	The origin and growth of supermassive black holes (SMBHs) within active galactic nuclei (AGNs) remain outstanding problems, particularly at high redshifts where the oldest SMBHs form and develop. Progress requires SMBH mass measurements at redshifts z ≳ 1, where estimates are sparse and difficult to obtain from ground-based surveys. Reverberation mapping (RM) uses a measured time lag between emission close to the SMBH and the response of gas in the broad-line region, with a measured gas velocity, to provide a virial SMBH mass. Single-epoch recipes use relations between these lags and luminosity to provide mass estimates for millions of quasars. However, these relations are tied to mostly local AGNs, and extrapolating them to high-z may induce bias. Thus RM mass estimates are needed at z ≳ 1, where reliable emission lines (e.g., Hβ) are shifted into the near-infrared. Similarly, continuum RM between photometric bands constrains the structure of the accretion disk. Physical models of AGN photometric variability also constrain the physics within the disk. Continuum RM is currently limited to ~20 local sources, so high-z estimates are required to trace SMBH growth. Studies of variability structure are sparse in the near-infrared, and require larger samples to trace high-z disk physics. We propose to use Roman's High-Latitude Time-Domain Survey (HLTDS) to perform the first large-scale near-infrared RM survey on thousands of AGNs in Euclid Deep Field South (EDFS). Within the first two years of Roman, we will obtain dozens of mass measurements, anchoring high-z single-epoch recipes. With joint Roman-Rubin EDFS photometry, we will perform continuum RM for high-mass z ≳ 1 AGNs. Finally, we will use combined HLTDS and High-Latitude Wide-Area Survey photometry for thousands of AGNs in EDFS and COSMOS to constrain the structure of near-infrared variability. These analyses will produce a legacy dataset of AGN variability data invaluable for future high-z quasar studies.