Little Red Dots on FIRE: The Ability of Bursty Galaxies to Host an Abundant Population of High-redshift AGN

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Abstract
The James Webb Space Telescope has unveiled an abundant population of potential active galactic nuclei (AGN) at high redshift ( z ≳ 4) known as little red dots (LRDs), which are likely hosted in relatively low-mass galaxies. However, previous theoretical models have highlighted the difficulty in continuously feeding massive black holes in the central regions of bursty, high-redshift galaxies because of repeated gas evacuation by stellar feedback. We analyze galaxies in high-redshift FIRE-2 simulations to understand whether they are capable of hosting the observed abundant population of high-redshift AGN. We use a gravitational torque-driven accretion (GTDA) model and a simple freefall accretion model to derive black hole accretion rates and construct predicted AGN bolometric luminosity functions for z = 5–7. The GTDA model and the freefall model with black holes accreting ≲1% of their central gas supply (M BH ≳ 2 × 10 5 M ⊙ black holes residing in M ⋆ ≳ 2 × 10 7 M ⊙ galaxies. We show that, under simple assumptions, mock observations of such sources can reproduce key observed LRD characteristics.
Funding Information
  • National Science Foundation (AST-2108230)
  • National Science Foundation (AST-2307327)
  • National Aeronautics and Space Administration (80NSSC22K1124)
  • National Aeronautics and Space Administration (21-ATP21-0036)
  • National Aeronautics and Space Administration (23-ATP23-0008)
  • Space Telescope Science Institute (JWST-AR-03252.001-A)
  • National Science Foundation (AST-2442788)
  • National Aeronautics and Space Administration (ATP23-0156)
  • Space Telescope Science Institute (JWST-GO-01712.009-A)
  • Space Telescope Science Institute (JWST-AR-04357.001-A)
  • Space Telescope Science Institute (JWST-AR-05366.005-A)

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