The incidence and properties of present-day dwarf galaxies hosting massive black holes ( BHs ) can provide important constraints on the origin of high-redshift BH seeds .
Here we present high-resolution X-ray and radio observations of the low-metallicity , star-forming , dwarf-galaxy system Mrk 709 with the Chandra X-ray Observatory and the Karl G. Jansky Very Large Array ( VLA ) .
These data reveal spatially coincident hard X-ray and radio point sources with luminosities suggesting the presence of an accreting massive BH ( M _ { BH } \sim 10 ^ { 5 - 7 } M _ { \odot } ) .
Based on imaging from the Sloan Digital Sky Survey ( SDSS ) , we find that Mrk 709 consists of a pair of compact dwarf galaxies that appear to be interacting with one another .
The position of the candidate massive BH is consistent with the optical center of the southern galaxy ( Mrk 709 S ) , while no evidence for an active BH is seen in the northern galaxy ( Mrk 709 N ) .
We derive stellar masses of M _ { \star } \sim 2.5 \times 10 ^ { 9 } ~ { } M _ { \odot } and M _ { \star } \sim 1.1 \times 10 ^ { 9 } ~ { } M _ { \odot } for Mrk 709 S and Mrk 709 N , respectively , and present an analysis of the SDSS spectrum of the BH-host Mrk 709 S. At a metallicity of just \sim 10 % solar , Mrk 709 is among the most metal-poor galaxies with evidence for an active galactic nucleus .
Moreover , this discovery adds to the growing body of evidence that massive BHs can form in dwarf galaxies and that deep , high-resolution X-ray and radio observations are ideally suited to reveal accreting massive BHs hidden at optical wavelengths .