1. The Rise of Faint, Red AGN at $z>4$: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields
- Author
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Kocevski, Dale D., Finkelstein, Steven L., Barro, Guillermo, Taylor, Anthony J., Calabrò, Antonello, Laloux, Brivael, Buchner, Johannes, Trump, Jonathan R., Leung, Gene C. K., Yang, Guang, Dickinson, Mark, Pérez-González, Pablo G., Pacucci, Fabio, Inayoshi, Kohei, Somerville, Rachel S., McGrath, Elizabeth J., Akins, Hollis B., Bagley, Micaela B., Bisigello, Laura, Bowler, Rebecca A. A., Carnall, Adam, Casey, Caitlin M., Cheng, Yingjie, Cleri, Nikko J., Costantin, Luca, Cullen, Fergus, Davis, Kelcey, Donnan, Callum T., Dunlop, James S., Ellis, Richard S., Ferguson, Henry C., Fujimoto, Seiji, Fontana, Adriano, Giavalisco, Mauro, Grazian, Andrea, Grogin, Norman A., Hathi, Nimish P., Hirschmann, Michaela, Huertas-Company, Marc, Holwerda, Benne W., Illingworth, Garth, Juneau, Stéphanie, Kartaltepe, Jeyhan S., Koekemoer, Anton M., Li, Wenxiu, Lucas, Ray A., Magee, Dan, Mason, Charlotte, McLeod, Derek J., McLure, Ross J., Napolitano, Lorenzo, Papovich, Casey, Pirzkal, Nor, Rodighiero, Giulia, Santini, Paola, Wilkins, Stephen M., and Yung, L. Y. Aaron
- Subjects
Astrophysics - Astrophysics of Galaxies - 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., Comment: 23 pages, 17 figures, submitted to ApJ
- Published
- 2024