On the X-ray properties of OH megamaser sources: Chandra snapshot observations

We present Chandra snapshot observations for a sample of seven sources selected from the Arecibo OH megamaser (OHM) survey at z~ 0.13-0.22 and with far-infrared (FIR) luminosities in excess of 10¹¹L_solar. In contrast with the known H₂O megamasers, which are mostly associated with powerful active galactic nuclei (AGN), the situation is far less clear for OHMs, which have been poorly studied in the X-ray band thus far. All of the observed sources are X-ray weak, with only one OHM, IRAS FSC 03521+0028 (z= 0.15), being detected by Chandra (with five counts). The results from this pilot programme indicate that the X-ray emission, with luminosities of less than ~10⁴²ergs^-1, is consistent with that from star formation (as also suggested in some cases by the optical spectra) and low-luminosity active galactic nuclei (LLAGN) emission. If an AGN is present, its contribution to the broad-band emission of OHM galaxies is likely modest. Under reasonable assumptions about the intrinsic X-ray spectral shape, the observed count distribution from stacking analysis suggests absorption of ~10²²cm^-2.