Co-evolution and Nuclear Structure in the Dwarf Galaxy POX 52 Studied by Multi-wavelength Data From Radio to X-ray

Abstract

The nearby dwarf galaxy POX 52 at \(z = 0.021\) hosts an active galactic nucleus (AGN) with a black-hole (BH) mass of \(M_{\rm BH} \sim 10^{5-6} M_\odot\) and an Eddington ratio of \(\sim\) 0.1-1. This object provides the rare opportunity to study both AGN and host-galaxy properties in a low-mass highly accreting system. To do so, we collected its multi-wavelength data from X-ray to radio. First, we construct a spectral energy distribution, and by fitting it with AGN and host-galaxy components, we constrain AGN-disk and dust-torus components. Then, while considering the AGN-disk emission, we decompose optical HST images. As a result, it is found that a classical bulge component is probably present, and its mass (\(M_{\rm bulge}\)) is consistent with an expected value from a local relation. Lastly, we analyze new quasi-simultaneous X-ray (0.2-30 keV) data obtained by NuSTAR and XMM-Newton. The X-ray spectrum can be reproduced by multi-color blackbody, warm and hot coronae, and disk and torus reflection components. Based on this, the spin is estimated to be \(a_{\rm spin} = 0.998_{-0.814}\), which could suggest that most of the current BH mass was achieved by prolonged mass accretion. Given the presence of the bulge, POX 52 would have undergone a galaxy merger, while the \(M_{\rm BH}\)-\(M_{\rm bulge}\) relation and the inferred prolonged accretion could suggest that AGN feedback occurred. Regarding the AGN structure, the spectral slope of the hot corona, its relative strength to the bolometric emission, and the torus structure are found to be consistent with Eddington-ratio dependencies found for nearby AGNs.