An Ultraluminous Supersoft Source in a Dwarf Galaxy of Abell 85: An Intermediate-Mass Black Hole Candidate

Abstract

We study a large sample of dwarf galaxies using archival Chandra X-ray observations, with the aim of detecting accreting intermediate-mass black holes (IMBHs). IMBHs are expected to inhabit dwarf galaxies and to produce specific signatures in terms of luminosity and X-ray spectra. We report the discovery of an X-ray source associated with an Abell 85 dwarf galaxy that fits the IMBH description. The stellar mass of the host galaxy is estimated to be 2 $\times$ 10${}^8$ $M_{\odot }$, which makes it one of the least massive galaxies to potentially host an accreting black hole. The source is detected in the soft band, under 1 keV, while undetected at higher energies. The X-ray luminosity is $\approx$ 10${}^{41}$ erg s${}^{-1}$, making it almost three orders of magnitude more luminous than the most luminous stellar-mass supersoft emitters. From the galaxy stellar mass vs. black hole mass relation, we estimate the mass to be within the intermediate regime. Another method that resulted in an intermediate mass relies on the fact that supersoft emission is expected to be associated with high accretion rates, approaching the Eddington limit. We suggest that the observed offset of the X-ray source from the galactic center ($\approx$ 1.8 kpc) is due to galaxy interactions, and we present evidence from the literature that supports the relation between black hole activity and galaxy interactions.

Accepted for publication in ApJ

References in corpus (8)

• Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey
• The powerful jet of an off-nuclear intermediate-mass black hole in the spiral galaxy NGC 2276
• WINGS: A WIde-field Nearby Galaxy-cluster Survey. II. Deep optical photometry of 77 nearby clusters
• An X-ray Selected Sample of Candidate Black Holes in Dwarf Galaxies
• X-ray Detected AGN in SDSS Dwarf Galaxies
• An Improved Age-Activity Relationship for Cool Stars older than a Gigayear
• Mass, Spin, and Ultralight Boson Constraints from the Intermediate Mass Black Hole in the Tidal Disruption Event 3XMM J215022.4-055108
• Black hole fueling in galaxy mergers: A high-resolution analysis

Cited by in corpus (4)

• Microlensing of gravitational waves by dark matter structures
• High-Energy Neutrinos from Gamma-Ray-Faint Accretion-Powered Hypernebulae
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies
• Merger rates of intermediate-mass black hole binaries in nuclear star clusters