James Webb Space Telescope Feed Post

Date: 6/10/2024

Harvard ADS: A Census of Photometrically Selected Little Red Dots at 4 < z < 9 in JWST Blank Fields

Paper abstract: Observations with the James Webb Space Telescope (JWST) have uncovered numerous faint active galactic nuclei (AGN) at z ~ 5 and beyond. These objects are key to our understanding of the formation of supermassive black holes (SMBHs), their coevolution with host galaxies, as well as the role of AGN in cosmic reionization. Using photometric colors and size measurements, we perform a search for compact red objects in an array of blank deep JWST/NIRCam fields totaling ~640 arcmin2. Our careful selection yields 260 reddened AGN candidates at 4 < z phot < 9, dominated by a point-source-like central component (eff> < 130 pc) and displaying a dichotomy in their rest-frame colors (blue UV and red optical slopes). Quasar model fitting reveals our objects to be moderately dust-extincted (A V ~ 1.6), which is reflected in their inferred bolometric luminosities of L bol = 1044–47 erg s-1 and fainter UV magnitudes M UV ? -17 to -22. Thanks to the large areas explored, we extend the existing dusty AGN luminosity functions to both fainter and brighter magnitudes, estimating their number densities to be ×100 higher than for UV-selected quasars of similar magnitudes. At the same time, they constitute only a small fraction of all UV-selected galaxies at similar redshifts, but this percentage rises to ~10% for M UV ~ - 22 at z ~ 7. Finally, assuming a conservative case of accretion at the Eddington rate, we place a lower limit on the SMBH mass function at z ~ 5, finding it to be consistent with both theory and previous JWST observations.