X‐Ray Emission from Megamaser Galaxy IC 2560

Observation of the H2O megamaser galaxy IC 2560 with the Chandra Observatoryreveals a complex spectrum composed of soft X-ray emission due tomulti-temperature thermal plasma, and a hard continuum with strong emissionlines. The continuum is most likely a Compton reflection (reprocessing) ofprimary emission that is completely absorbed at least up to 7 keV. The linescan be identified with fluorescence from Si, S and Fe in the lowest ionizationstages. The equivalent widths of the Si and S lines are broadly compatible withthose anticipated for reprocessing by optically thick cold plasma of Solarabundances, while the large equivalent width of the Fe line requires someoverabundance of iron. A contribution to the line from a transmitted componentcannot be ruled out, but the limits on the strength of the Compton shouldermake it less likely. From the bolometric luminosity of the nuclear region, weinfer that the source radiates at 1 - 10% of its Eddington luminosity, for anadopted central mass of 3 million Solar masses. The overall spectrum isconsistent with the hypotheses that the central engines powering the detectedmegamsers in accretion disks are obscured from direct view by the associatedaccretion disk material itself, and that there is a correlation between theoccurrence of megamaser emission and Compton-thick absorption columns. For the11 known galaxies with both column density measurements and maser emissionbelieved to arise from accretion disks, eight AGN are Compton thick.Comment: Accepted by the Astrophysical Journa