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Arxiv: Little Red Dots: an abundant population of faint AGN at z\sim5 revealed by the EIGER and FRESCO JWST surveys Published: 6/8/2023 9:00:00 PM Updated: 1/23/2024 11:59:22 AM

Paper abstract: Characterising the prevalence and properties of faint active galactic nuclei(AGN) in the early Universe is key for understanding the formation ofsupermassive black holes (SMBHs) and determining their role in cosmicreionization. We perform a spectroscopic search for broad H\alpha emitters atz~4-6 using deep JWST/NIRCam imaging and wide field slitlessspectroscopy from the EIGER and FRESCO surveys. We identify 20 H\alpha linesat z = 4.2 - 5.5 that have broad components with line widths from ~1200 -3700 km s^{-1}, contributing ~ 30 - 90 % of the total line flux. Weinterpret these broad components as being powered by accretion onto SMBHs withimplied masses ~10^{7-8} M_{\odot}. In the UV luminosity range M_{\rmUV, AGN+host} = -21 to -18, we measure number densities of ~10^{-5}cMpc^{-3}. This is an order of magnitude higher than expected fromextrapolating quasar UV luminosity functions. Yet, such AGN are found in only<1% of star-forming galaxies at z~5. The number density discrepancy ismuch lower when compared to the broad H\alpha luminosity function. The SMBHmass function agrees with large cosmological simulations. In two objects wedetect complex H\alpha profiles that we tentatively interpret as caused byabsorption signatures from dense gas fueling SMBH growth and outflows. We maybe witnessing early AGN feedback that will clear dust-free pathways throughwhich more massive blue quasars are seen. We uncover a strong correlationbetween reddening and the fraction of total galaxy luminosity arising fromfaint AGN. This implies that early SMBH growth is highly obscured and thatfaint AGN are only minor contributors to cosmic reionization.