The Properties of Little Red Dot Galaxies in the ASTRID Simulation

We present simulated counterparts of the ``Little Red Dot’’ (LRD) galaxies observed with JWST, using the large cosmological hydrodynamic simulation, ASTRID. We create mock observations of the galaxies (\(5 \leq z \leq 8\)) in ASTRID, and find seventeen which fit the color and size criteria of LRDs. These LRDs are galaxies with high stellar masses (\(\rm log(M_*/M_{\odot}) \geq 9.7\)), and massive black holes (\(\rm log(M_{BH}/M_{\odot}) \geq 6.8\)). The host galaxies are dense, with stellar half mass radii (\(\rm 325\,pc \leq r_{{\rm half},*} \leq 620\,pc\)), and dust attenuation in the F444W band above 1.25. Their star formation has been recently quenched. They host relatively bright AGN that are dust-obscured and contribute significantly to the rest-frame optical red slope and have relatively low luminosity in the rest-frame ultraviolet, where the host galaxy’s stars are more dominant. These LRDs are in an evolutionary phase of miniquenching that is the result of AGN feedback from their massive black holes. The LRDs in ASTRID are bright with F444W magnitudes of \(23.5-25.5\). The less massive and fainter galaxies in ASTRID lack the dust concentration necessary to produce the red slope of an LRD, though this could be an effect of limited resolution. Most of the highest Eddington black holes are not LRDs due to insufficient dust attenuation from their host galaxies, which are also experiencing relatively high star formation rates. This results in their spectra being too flat, despite their highly accreting black holes.