Searching Water Megamasers By Using Mid-infrared Spectroscopy (I): Possible Mid-infrared Indicators

Abstract

Water megamasers at 22 GHz with a gas disk configuration in galaxies provide the most precise measurements of supermassive black hole masses, as well as independent constraints on the Hubble constant in the nearby universe. The existence of other maser types, such as jet or outflow masers, represents another tracer for AGN science. However, the detection rate of water megamasers in galaxies is extremely low. Over 40 years, only $\sim$ 160 galaxies are found to harbour maser emission, and $\sim$ 30\% of them show features in their maser emission that indicate a disk-like geometry. Therefore, increasing the detection rate of masers is a crucial task to allow expanding on maser studies. We present a comparison of mid-infrared spectroscopic data between a maser galaxy sample and a Seyfert 2 control sample. We find that maser galaxies show significant peculiarities in their mid-infrared spectra: (1) Maser galaxies tend to present stronger silicate absorption at $\tau$ 9.7 $\mu$m than the control sample, (2) PAH 11.3 $\mu$m emission in maser galaxies is much weaker than in the control sample, (3) spectral indices at 20-30 $\mu$m are steeper in maser galaxies than in the control sample and tend to be mid-infrared enhanced population. We conclude that there may be good indicators in mid-infrared and far-infrared which could differentiate maser and non-maser Seyfert 2 galaxies. Upcoming infrared facilities, such as the James Webb Space Telescope, may be able to exploit these and other useful criteria and tracers for water megamaser observations.

11 pages, 6 figures, 1 appendix; accepted for publication in MNRAS

References in corpus (12)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints
• Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust
• The distribution of silicate strength in Spitzer spectra of AGNs and ULIRGs
• Spitzer/IRS 5-35 um Low-Resolution Spectroscopy of the 12 um Seyfert Sample
• Nuclear 11.3$\mu$m PAH emission in local active galactic nuclei
• Mid-Infrared Properties of Luminous Infrared Galaxies II: Probing the Dust and Gas Physics of the GOALS Sample
• Prevalence of High X-ray Obscuring Columns among AGN that Host H${}_2$O Masers
• PAH features within few hundred parsecs of active galactic nuclei
• Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities
• Water megamaser emission in hard X-ray selected AGN