The Rise of Faint, Red AGN at \(z>4\): A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields

Abstract

We present a sample of 341 "little red dots" (LRDs) spanning the redshift range \(z\sim2-11\) using data from the CEERS, PRIMER, JADES, UNCOVER and NGDEEP surveys. These sources are likely heavily-reddened AGN that trace a previously-hidden phase of dust-obscured black hole growth in the early Universe. Unlike past use of color indices to identify LRDs, we employ continuum slope fitting using shifting bandpasses to sample the same rest-frame emission blueward and redward of the Balmer break. This approach allows us to identify LRDs over a wider redshift range and is less susceptible to contamination from galaxies with strong breaks that otherwise lack a rising red continuum. The redshift distribution of our sample increases at \(z<8\) and then undergoes a rapid decline at \(z\sim4.5\), which may tie the emergence, and obscuration, of these sources to the inside-out growth that galaxies experience during this epoch. We find that LRDs are 2-3 dex more numerous than bright quasars at \(z\sim5-7\), but their number density is only 0.6-1 dex higher than X-ray and UV selected AGN at these redshifts. Within our sample, we have identified the first X-ray detected LRDs at \(z=3.1\) and \(z=4.66\). An X-ray spectral analysis confirms that these AGN are moderately obscured with \(\log\,(N_{\rm H}/{\rm cm}^{2}\)) of \(23.3^{+0.4}_{-1.3}\) and \(22.72^{+0.13}_{-0.16}\). Our analysis reveals that reddened AGN emission dominates their rest-optical light, while the rest-UV originates from their host galaxies. We also present NIRSpec follow-up spectroscopy of 17 LRDs that show broad emission lines consistent with AGN activity. The confirmed AGN fraction of our sample is \(71\%\) for sources with F444W\(<26.5\). In addition, we find three LRDs with narrow blue-shifted Balmer absorption features in their spectra, suggesting an outflow of high-density, low ionization gas from near the central engine of these faint, red AGN.