Little Red Dot $-$ Host Galaxy $=$ Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot
Wendy Q. Sun, Rohan P. Naidu, Jorryt Matthee, Anna de Graaff, John Chisholm, Jenny E. Greene, Pascal A. Oesch, Alberto Torralba, Raphael E. Hviding, Gabriel Brammer, Robert A. Simcoe, Sownak Bose, Rychard Bouwens, Pratika Dayal, Anna-Christina Eilers, Qinyue Fei, Lukas J. Furtak

TL;DR
This study presents evidence that black hole stars, dense gas-enshrouded early black hole growth stages, are common in Little Red Dots, characterized by specific spectral features and often linked to starburst activity in low-mass galaxies.
Contribution
It introduces a novel spectral decomposition method to identify black hole stars in high-redshift galaxies, providing population-level evidence of their prevalence and properties.
Findings
Black hole stars dominate the emission at wavelengths longer than Hα.
Black hole stars are prevalent in low-mass, starbursting galaxies.
Black hole stars have a transient duty cycle of about 1%.
Abstract
The central engines of Little Red Dots (LRDs) may be ``black hole stars" (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [OIII]5008\r{A} line arises exclusively from the host. Using a sample of 98 LRDs (~) with high quality NIRSpec/PRISM spectra, we demonstrate that the host-subtracted median stack displays a Balmer break stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED (~ K, ~ erg s, ~ au). We measure a steep Balmer decrement…
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Taxonomy
TopicsAstrophysical Phenomena and Observations · Galaxies: Formation, Evolution, Phenomena · Astronomy and Astrophysical Research
