Beyond the Bright Tail: Faint Reionization-Era Quasars with Archival Roman Grism Data

Beyond the Bright Tail: Faint Reionization-Era Quasars with Archival Roman Grism Data

Program ID	19108
Science Category	Active Galaxies & Supermassive Black Holes
Program Type	Analysis
Category	Small
Principal Investigator	Mainak Singha
PI Institution	Catholic University of America
Co-Investigators	Sangeeta Malhotra (NASA Goddard Space Flight Center) James Rhoads (NASA Goddard Space Flight Center) Isak Wold (Catholic University of America) Wei Leong Tee (Pennsylvania State University)
Abstract	We propose to build and validate an end-to-end framework for identifying faint z >= 7.5 quasars in Roman HLWAS Medium and converting those detections into calibrated abundance constraints using archival Roman data as they become available. Recent work has shown that the early accreting black-hole population extends beyond the classical luminous-quasar regime, but the faint end remains poorly constrained because existing surveys trade area against depth. Roman HLWAS Medium is the key regime for this problem: it combines survey-scale area with grism spectroscopy and supporting F106/F129/F158 imaging, enabling both candidate selection and direct calibration of the selection function. Our program will use archival Roman imaging and slitless spectroscopy to measure the completeness surface C(J,z), characterize contamination from low-redshift interlopers, and determine the depth at which faint quasars can be recovered with robust spectral confirmation. We will build a contamination-aware selection function, quantify recovery of the faint-end abundance over a range of luminosity-function models, and map the regime in which HLWAS Medium can constrain the quasar luminosity function at z >= 7.5. A central goal is to establish whether the HLWAS Medium combination of wide area, multi-band imaging, and 1.0-1.93 um grism coverage can recover the faint population required to measure the abundance slope near M1450 ~ -22. The deliverables are practical, archival, and community-facing. We will release candidate catalogs, extracted 1D spectra, completeness and contamination products, abundance-inference tools, and documented analysis workflows through standard community channels, enabling direct reuse on Roman survey products. This program will provide the quantitative bridge between archival Roman data and the first calibrated survey-scale constraints on the faint high-redshift quasar population.