‘Little red dots’ cannot reside in the same dark matter haloes as comparably luminous unobscured quasars

Monthly Notices of the Royal Astronomical Society, vol. 539, pp. 2910–2925

Abstract

ABSTRACT The JWST has uncovered a new population of candidate broad-line active galactic nucleus (AGN) emerging in the early Universe, named ‘little red dots’ (LRDs) because of their compactness and red colours at optical wavelengths. LRDs appear to be surprisingly abundant (${\approx} 10^{-5} \, {\rm cMpc}^{-3}$) given that their inferred bolometric luminosities largely overlap with those of the ultraviolet (UV)-luminous quasars identified at high z in wide-field spectroscopic surveys. In this work, we investigate how the population of LRDs and/or other UV-obscured AGN relates to the one of unobscured, UV-selected quasars. By comparing their number densities, we infer an extremely large and rapidly evolving obscured:unobscured ratio, ranging from ${\approx} 20{:}1$ at $z\approx 4$ to ${\approx} 2300{:}1$ at $z\approx 7$, and possibly extending out to very high (${\approx} 10^{47}\, {\rm erg}\, {\rm s}^{-1}$) bolometric luminosities. This large obscured:unobscured ratio is incompatible with the UV-luminous duty cycle measured for unobscured quasars at $z\approx 4\!-\!6$, suggesting that LRDs are too abundant to be hosted by the same haloes as unobscured quasars. This implies that either (a) the bolometric luminosities of LRDs are strongly overestimated or (b) LRDs follow different scaling relations than those of UV-selected quasars, representing a new population of accreting supermassive black holes emerging in the early Universe. A direct comparison between the clustering of LRDs and that of faint UV-selected quasars will ultimately confirm these findings and shed light on key properties of LRDs such as their host mass distribution and duty cycle. We provide a mock analysis for the clustering of LRDs and show that it is feasible with current and upcoming JWST surveys.

Authors 7

1. Elia Pizzati corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden ,

   Leiden Observatory , Leiden University, P.O. Box 9513, 2300 RA Leiden,

2. Joseph F. Hennawi Aachen Leiden Observatory

   Leiden University · University of California, Santa Barbara · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden ,

   University of California Department of Physics, , Santa Barbara, CA 93106 ,

   Department of Physics, University of California , Santa Barbara, CA 93106,

   Leiden Observatory , Leiden University, P.O. Box 9513, 2300 RA Leiden,

3. Joop Schaye Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden ,

   Leiden Observatory , Leiden University, P.O. Box 9513, 2300 RA Leiden,

4. Anna–Christina Eilers

   Massachusetts Institute of Technology

   Affiliation as printed

   MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139 ,

   MIT Kavli Institute for Astrophysics and Space Research , Massachusetts Institute of Technology, Cambridge, MA 02139,

5. Jiamu Huang

   University of California, Santa Barbara

   Affiliation as printed

   University of California Department of Physics, , Santa Barbara, CA 93106 ,

   Department of Physics, University of California , Santa Barbara, CA 93106,

6. Jan–Torge Schindler

   Universität Hamburg

   Affiliation as printed

   Hamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, D-21029 Hamburg ,

   Hamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, D-21029 Hamburg,

7. Feige Wang

   University of Michigan · University of Arizona

   Affiliation as printed

   Steward Observatory, University of Arizona , 933 N Cherry Avenue, Tucson, AZ 85721 ,

   University of Michigan Department of Astronomy, , 1085 S University Ave, Ann Arbor, MI 48109 ,

   Department of Astronomy, University of Michigan , 1085 S. University Ave., Ann Arbor, MI 48109,

   Steward Observatory, University of Arizona , 933 N Cherry Avenue, Tucson, AZ 85721,