Local Analogs of Primordial Galaxies: In Search of Intermediate Mass Black Holes with JWST NIRSpec

Abstract

Local low metallicity galaxies with signatures of possible accretion activity are ideal laboratories in which to search for the lowest mass black holes and study their impact on the host galaxy. Here we present the first JWST NIRSpec IFS observations of SDSS J120122.30+021108.3, a nearby (z=0.00354) extremely metal poor dwarf galaxy with no optical signatures of accretion activity but identified by WISE to have extremely red mid-infrared colors consistent with AGNs. We identify over one hundred lines between ∼ 1.7-5.2 microns, an unresolved nuclear continuum source with an extremely steep spectral slope consistent with hot dust from an AGN (Fᵥ≈ν⁻¹˙⁵), and a plethora of H I, He I, and H₂ lines, with no lines from heavier elements, CO or ice absorption features, or PAHs. Our observations reveal that the red WISE source arises exclusively from a bright central unresolved source (< 3pc) suggestive of an AGN, yet there are no He II lines or coronal lines identified in the spectrum, and, importantly, there is no evidence that the radiation field is harder in the nuclear source compared with surrounding regions. These observations can be explained with a young (< 5 Myr) nuclear star cluster with stellar mass ∼3×10⁴ M⊙ and a deeply embedded AGN with bolometric luminosity ∼ 2×10⁴¹ ergs ⁻¹. The implied black hole mass is ∼ 1450 M⊙, based on the Eddington limit, roughly consistent with that expected based on extrapolations of black hole galaxy scaling relations derived for more massive black holes. Longer wavelength observations are crucial to confirm this scenario.