Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts

Abstract The birth of seeds of massive black holes (BHs) and nascent galaxies at cosmic dawn takes place in dense gaseous environments, which play a crucial role in shaping their coevolution and radiation spectra. We investigate gas accretion during the assembly of massive halos with M h ≳ 10 10 −10 11 M ⊙ at redshifts z ≃ 4–10, driving both rapid BH feeding and concurrent nuclear starbursts. As the BH grows to ∼10 6 −10 7 M ⊙ via super-Eddington accretion, the accretion power inflates a dense envelope whose effective temperature approaches the Hayashi limit at T eff ≃ 5000 K, producing red optical emission, while a coeval young stellar population of ∼10 7 M ⊙ provides blue UV emission. This early coevolving…

• NA
  National Aeronautics and Space Administration

  Awards: 5-03127, NAS 5-03127
• ST
  Space Telescope Science Institute

  Awards: 5-03127, NAS 5-03127
• NN
  National Natural Science Foundation of China

  Awards: 2022YFF0503401, 12473037, 12233001
• PU
  Peking University
• YI
  Yukawa Institute for Theoretical Physics, Kyoto University
• JS
  Japan Society for the Promotion of Science

  Awards: JP23H04899, JP22H00130, JP24K00668