N_H - N_HI correlation in Gigahertz-peaked-spectrum galaxies

Abstract

With the Westerbork Synthesis Radio Telescope, we performed HI observations of a sample of known X-ray emitting Gigahertz-peaked-spectrum galaxies with compact-symmetric-object morphology (GPS/CSOs) that lacked an HI absorption detection. We combined radio and X-ray data of the full sample of X-ray emitting GPS/CSOs and found a significant, positive correlation between the column densities of the total and neutral hydrogen ($N_{\mathrm{H}}$ and $N_{\mathrm{HI}}$, respectively). Using a Bayesian approach, we simultaneously quantified the parameters of the $N_{\mathrm{H}}-N_{\mathrm{HI}}$ relation and the intrinsic spread of the data set. For a specific subset of our sample, we found $N_{\mathrm{H}}\propto N_{\mathrm{HI}}^b$, with $b=0.93_{-0.33}^{+0.49}$, and $\ddot{I}{ƒ}_{int}(N_{\mathrm{H}})=1.27_{-0.40}^{+1.30}$. The $N_{\mathrm{H}}-N_{\mathrm{HI}}$ correlation suggests a connection between the physical properties of the radio and X-ray absorbing gas.

6 pages, 3 figures, in press for Astronomische Nachrichten. Contribution to the Proceedings of the "Fifth Workshop on Compact Steep Spectrum and GHz-Peaked Spectrum Radio Sources", held in Rimini (Italy) in May 2015