HSC-XD 52: An X-ray detected AGN in a low-mass galaxy at $z\sim0.56$

TL;DR

This paper reports the discovery and analysis of HSC-XD 52, a luminous X-ray detected active galactic nucleus in a low-mass galaxy at redshift 0.56, providing insights into black hole growth in dwarf galaxies.

Contribution

It presents the first spectroscopic confirmation of a low-mass AGN at intermediate redshift with detailed properties, expanding understanding of black hole evolution in dwarf galaxies.

Findings

Stellar mass of the host galaxy is approximately 3 x 10^9 solar masses.

Black hole mass estimated at around 10^6 solar masses.

X-ray luminosity is about 3.5 x 10^43 erg/s, among the most luminous in dwarf galaxies.

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 $z\sim0.56$. 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.