학술논문
The Rise of Faint, Red AGN at $z>4$: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields
Document Type
Working Paper
Author
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.; Yung, L. Y. Aaron
Source
Subject
Language
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
Comment: 23 pages, 17 figures, submitted to ApJ