Accretion from Winds of Red Giant Branch Stars May Reveal the Supermassive Black Hole in Leo I

Abstract

Abstract A supermassive black hole (SMBH) of ∼3 × 106 M ⊙ was recently detected via dynamical measurements at the center of the dwarf galaxy Leo I. Standing ∼2 orders of magnitude above standard scaling relations, this SMBH is hosted by a galaxy devoid of gas and with no significant star formation in the last ∼1 Gyr. This detection can profoundly impact the formation models for black holes and their hosts. We propose that winds from a population of ∼100 evolved stars within the Bondi radius of the SMBH produce a sizable accretion rate, with Eddington ratios between 9 × 10−8 and 9 × 10−7, depending on the value of the stellar mass loss. These rates are typical of SMBHs accreting in advection-dominated accretion flow mode. The predicted spectrum peaks in the microwaves at ∼0.1–1 THz (300–3000 μm) and exhibits significant variations at higher energies depending on the accretion rate. We predict a radio flux of ∼0.1 mJy at 6 GHz, mildly dependent on the accretion properties. Deep imaging with Chandra, the Very Large Array, and the Atacama Large Millimeter/submillimeter Array can confirm the presence of this SMBH and constrain its accretion flow.