Enhancing the Detection Rate of Megamasers Based on Optical and Mid-Infrared Photometry
Cheng-Yu Kuo4*, Anca Constantin1, James Braatz2, Hui-Hsuan Chung3
1physics, James Madison University, Harrisonburg, USA
2radio astronomy, National Radio Astronomy Observatory, Charlottesville, USA
3Physics, National Tsing Hua University, Hsingchu, USA
4Physics, National Sun Yat-Sen University, Kaosiung, Taiwan
* Presenter:Cheng-Yu Kuo, email:cykuo@mail.nsysu.edu.tw
H2O megamasers from circumnuclear disks (disk masers) in active galaxies provide an unique way to probe active galactic nuclei and allow accurate measurement of the mass of supermassive black holes and determination of the Hubble constant. Nonetheless, the detection rates of H2O megamasers and disk masers are typically 2.6\% and 1%, respectively. The low detection rate significantly limit the extent of applying megamasers to solve important astrophysical questions. To enhance the detection rate of H2O megamasers, we study the mid-infrared properties of maser host galaxies using photometry from the Wide-field Infrared Survey Explorer (WISE) and find that galaxies with megamaser emissions are enhanced in all mid-infrared wavelengths, with the enhancement strongest at 22 micron. In addition, the detection rate of megamasers depends substantially on all indicators of AGN strength in the mid-infrared, such as W1-W2, W1-W4, and the total mid-infrared luminosity of an AGN. The correlations between megamaser detection rate and the level of AGN activity allow us to boost the detection rate by a factor of 2-8. The resultant detection rate can range from 6% to 17%, depending on the chosen sample selection criteria. In addition to studying the mid-infrared properties, we also explore the correlations between megamasers and their optical properties. We find that adding the information of optical color and absolute g-band magnitude can help effectively boost the detection rate of disk masers with relatively high detection completeness.

Keywords: active galactic nuclei, water maser, megamaser, black hole, hubble constant