HSC-XD 52: An X-ray detected AGN in a low-mass galaxy at $z\sim 0.56$

Abstract

The properties of low-mass galaxies hosting central black holes provide clues about the formation and evolution of the progenitors of supermassive black holes. In this letter, we present HSC-XD 52, a spectroscopically confirmed low-mass active galactic nucleus (AGN) at an intermediate redshift of $z\sim 0.56$. We detect this object as a very luminous X-ray source coincident with a galaxy observed by the Hyper Suprime-Cam (HSC) as part of a broader search for low-mass AGN. We constrain its stellar mass through spectral energy distribution modeling to be LMC-like at $M_{\star }\approx 3\times 10^9{M}_{\odot }$, placing it in the dwarf regime. We estimate a central black hole mass of $M_{\mathrm{BH}}\sim 10^6{M}_{\odot }$. With an average X-ray luminosity of $L_X\approx 3.5\times 10^{43}\mathrm{erg}{\mathrm{s}}^{-1}$, HSC-XD 52 is among the most luminous X-ray selected AGN in dwarf galaxies. The spectroscopic and photometric properties of HSC-XD 52 indicate that it is an intermediate redshift counterpart to local low-mass AGN.

accepted to ApJL; 8 pages, 4 figures, 1 table