X-ray Emission from Megamaser Galaxy IC 2560

Abstract

Observation of the H2O megamaser galaxy IC 2560 with the Chandra Observatory reveals a complex spectrum composed of soft X-ray emission due to multi-temperature thermal plasma, and a hard continuum with strong emission lines. The continuum is most likely a Compton reflection (reprocessing) of primary emission that is completely absorbed at least up to 7 keV. The lines can be identified with fluorescence from Si, S and Fe in the lowest ionization stages. The equivalent widths of the Si and S lines are broadly compatible with those anticipated for reprocessing by optically thick cold plasma of Solar abundances, while the large equivalent width of the Fe line requires some overabundance of iron. A contribution to the line from a transmitted component cannot be ruled out, but the limits on the strength of the Compton shoulder make it less likely. From the bolometric luminosity of the nuclear region, we infer that the source radiates at 1 - 10% of its Eddington luminosity, for an adopted central mass of 3 million Solar masses. The overall spectrum is consistent with the hypotheses that the central engines powering the detected megamsers in accretion disks are obscured from direct view by the associated accretion disk material itself, and that there is a correlation between the occurrence of megamaser emission and Compton-thick absorption columns. For the 11 known galaxies with both column density measurements and maser emission believed to arise from accretion disks, eight AGN are Compton thick.

Accepted by the Astrophysical Journal

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• Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities
• Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945
• Low-luminosity Extragalactic Water Masers toward M82, M51, and NGC4051
• Optical Properties of Host Galaxies of Extragalactic Nuclear Water Masers
• On the nuclear obscuration of H2O maser galaxies
• The Difference in Narrow Fe KαLine Emission Between Seyfert 1 and Seyfert 2 Galaxies
• Water-Vapor Maser Disk at the Nucleus of the Seyfert 2 Galaxy IC 2560 and its Distance
• A Deep 0.3-10 keV Spectrum of the H${}_2$O Maser Galaxy IC 2560
• Suzaku Results on the Obscured Low-Luminosity Active Galactic Nucleus in NGC 4258
• Reflection-dominated nuclear X-ray emission in the early-type galaxy ESO 565--G019
• The study of Seyfert 2 galaxies with and without infrared broad lines
• Masers in AGN environments
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• Searches for H${}_2$O Masers toward Narrow-Line Seyfert 1 galaxies
• 21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies