2021/11/30 by Akos Bogdan, Ákos Bogdán, Orsolya E. Kovacs +11 · 6 citations
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Luminosity #Physics #Population #Quasar #Redshift #Reionization #Star formation #Supermassive black hole #astro-ph.GA #astro-ph.HE
paper · pdf · open access · doi:10.3847/1538-4357/ac4ae5
published in The Astrophysical Journal 927(1), 34 (IOP Publishing) · 14 pages, 5 figures, accepted for publication in The Astrophysical Journal
arxiv created 2022/01/12 · openalex publication_date 2022/03/01 · openalex created_date 2022/03/05 · arxiv updated 2022/03/14 · openalex updated_date 2026/08/06
Although observations of high-redshift quasars demonstrate that many supermassive black holes (BHs) reached large masses within one billion years after the Big Bang, the origin of the first BHs is still a mystery. A promising way to constrain the origin of the first BHs is to explore the average properties of z\gtrsim6 BHs. However, typical BHs remain hidden from X-ray surveys, which is due to their relatively faint nature and the limited sensitivity of X-ray telescopes. Gravitational lensing provides an attractive way to study this unique galaxy population as it magnifies the faint light from these high-redshift galaxies. Here, we study the X-ray emission originating from 155 gravitationally-lensed z\gtrsim6 galaxies that were detected in the RELICS survey. We utilize Chandra X-ray observations to search for AGN in the individual galaxies and in the stacked galaxy samples. We did not identify an individual X-ray source that was undoubtedly associated with a high-redshift galaxy. We stack the signal from all galaxies and do not find a statistically significant detection. We split our sample based on stellar mass, star-formation rate, and lensing magnification and stack these sub-samples. We obtain a 2.2σ detection for massive galaxies with an X-ray luminosity of (3.7±1.6)×1042 \rmerg s-1, which corresponds to a (3.0±1.3)×105 \rmM\odot BH accreting at its Eddington rate. Other stacks remain undetected and we place upper limits on the AGN emission. These limits imply that the bulk of BHs at z\gtrsim6 either accrete at a few percent of their Eddington rate and/or are 1-2 orders of magnitude less massive than expected based on the stellar mass of their host galaxy.