PREPRINT
A070A896-0728-40B6-9917-8F57B39825E0

NuSTAR observations of a heavily X-ray obscured AGN in the dwarf galaxy J144013+024744

Shrey. Ansh, Chien-Ting J. Chen, W. N. Brandt, Carol E. Hood, E. S. Kammoun, G. Lansbury, Stéphane Paltani, Amy E. Reines, C. Ricci, Douglas A. Swartz, Jonathan R. Trump, F. Vito, Ryan C. Hickox

Submitted on 20 September 2022

Abstract

We present a multi-wavelength analysis of the dwarf Seyfert-2 galaxy J$144013+024744$, a candidate obscured active galactic nucleus (AGN) thought to be powered by an intermediate-mass black hole (IMBH, ${M}_{\bullet }\approx {10}^{4-6}{M}_{\odot }$) of mass ${M}_{\bullet }\sim {10}^{5.2}{M}_{\odot }$. To study its X-ray properties, we targeted J$144013+024744$ with NuSTAR for $\approx 100$ ks. The X-ray spectrum was fitted with absorbed power law, Pexmon and a physical model (RXTorus). A Bayesian X-ray analysis was performed to estimate the posteriors. The phenomenological and the physical models suggest the AGN to be heavily obscured by a column density of ${N}_{\mathrm{H}}=\left(3.4-7.0\right)×{10}^{23}$ cm${}^{-2}$. In particular, the RXTorus model with a sub-solar metallicity suggests the obscuring column to be almost Compton-thick. We compared the $2-10$ keV intrinsic X-ray luminosity with the inferred X-ray luminosities based on empirical scaling relations for unobscured AGNs using ${L}_{\left[\mathrm{O}\mathrm{I}\mathrm{V}\right]\left(25.89\mu \mathrm{m}\right)}$, ${L}_{\left[\mathrm{O}\mathrm{I}\mathrm{I}\mathrm{I}\right]\left(5007\mathrm{a}\mathrm{n}\mathrm{g}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{m}\right)}$, and ${L}_{6\mu \mathrm{m}}$ and found that the high-excitation $\left[\mathrm{O}\mathrm{I}\mathrm{V}\right]$ line provides a better estimate of the intrinsic $2-10$ keV X-ray luminosity (${L}_{2-10}^{\mathrm{i}\mathrm{n}\mathrm{t}}\sim {10}^{41.41}{\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{s}}^{-1}$). Our results suggest that J$144013+024744$ is the first type-2 dwarf galaxy that shows X-ray spectroscopic evidence for obscuration. The column density that we estimated is among the highest measured to date for IMBH-powered AGNs, implying that a typical AGN torus geometry might extend to the low-mass end. This work has implications for constraining the black hole occupation fraction in dwarf galaxies using X-ray observations.

Preprint

Comment: Accepted for Publication in ApJ

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - High Energy Astrophysical Phenomena