A deep look at the nuclear region of UGC 5101 through high angular resolution mid-IR data with GTC/CanariCam

TL;DR

This study uses high-resolution mid-infrared data from GTC/CanariCam and other telescopes to analyze the obscuring material and properties of the active galactic nucleus in the ultraluminous IR galaxy UGC 5101, revealing a heavily obscured AGN with a large torus covering factor.

Contribution

It provides a detailed characterization of the AGN and its torus in UGC 5101 using high angular resolution mid-IR observations and advanced modeling techniques, which was not previously done with such detail.

Findings

The torus has a large covering factor and high foreground extinction.

The AGN bolometric luminosity is approximately 1.9×10^45 erg/s.

The properties are consistent with the lack of strong optical AGN signatures.

Abstract

We present an analysis of the nuclear infrared (IR, 1.6 to 18 $\mu$m) emission of the ultraluminous IR galaxy UGC 5101 to derive the properties of its active galactic nucleus (AGN) and its obscuring material. We use new mid-IR high angular resolution ($0.3-0.5$ arcsec) imaging using the Si-2 filter ($\lambda_{C}=8.7\, \mu$m) and $7.5-13$ $\mu$m spectroscopy taken with CanariCam (CC) on the 10.4m Gran Telescopio CANARIAS. We also use archival HST/NICMOS and Subaru/COMICS imaging and Spitzer/IRS spectroscopy. We estimate the near- and mid-IR unresolved nuclear emission by modelling the imaging data with GALFIT. We decompose the Spitzer/IRS and CC spectra using a power-law component, which represents the emission due to dust heated by the AGN, and a starburst component, both affected by foreground extinction. We model the resulting unresolved near- and mid-IR, and the starburst subtracted CC spectrum with the CLUMPY torus models of Nenkova et al. The derived geometrical properties of the torus, including the large covering factor and the high foreground extinction needed to reproduce the deep $9.7\, \mu$m silicate feature, are consistent with the lack of strong AGN signatures in the optical. We derive an AGN bolometric luminosity $L_{bol}\sim1.9\times10^{45}\,$erg s$^{-1}$ that is in good agreement with other estimates in the literature.