AGN X-Ray Irradiation of CO Gas in NGC 2110 Revealed by Chandra and ALMA

Journal article, 2020

We report spatial distributions of the Fe-K alpha line at 6.4 keV and the CO(J = 2-1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at 05. A Chandra 6.2-6.5 keV to 3.0-6.0 keV image suggests that the Fe-K alpha emission extends preferentially in a northwest to southeast direction out to 3 '', or similar to 500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe-K alpha emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be similar to 1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2-1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H-2. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.