Enhancing the H2O Megamaser Detection Rate Using Optical and Mid-infrared Photometry

TL;DR

This study investigates how optical and mid-infrared photometric properties of galaxies can be used to significantly increase the detection rate of water megamasers, which are crucial for measuring black hole masses and cosmological parameters.

Contribution

It introduces a multivariate parameter analysis linking galaxy photometry to megamaser presence, proposing new criteria to boost detection rates by up to 15%.

Findings

Megamaser-hosting galaxies show strong mid-infrared emission, especially at 22 microns.

Red W1-W2 and W1-W4 colors correlate with megamaser presence.

Detection rates could increase to 6-15% using new photometric selection criteria.

Abstract

Water megamasers from circumnuclear disks in galaxy centers provide the most accurate measurements of supermassive black hole masses and uniquely probe the sub-parsec accretion processes. At the same time, these systems offer independent crucial constraints of the Hubble Constant in the nearby universe, and thus, the arguably best single constraint on the nature of dark energy. The chances of finding these golden standards are however abysmally low, at an overall =< 3% for any level of water maser emission detected at 22 GHz, and =< 1% for those exhibiting the disk-like configuration. We provide here a thorough summary of the current state of the detection of water megamaser disks, along with a novel investigation of the likelihood of increasing their detection rates based on a multivariate parameter analysis of optical and mid-infrared photometric properties of the largest database of galaxies surveyed for the 22 GHz emission. We find that galaxies with water megamaser emission tend to associate with strong emission in all WISE mid-infrared wavelengths, with the strongest enhancement in the W4 band, at 22 micron, as well as with previously proposed and newly found indicators of AGN strength in the mid-infrared, such as red W1-W2 and W1-W4 colors, and the integrated mid-infrared luminosity of the host galaxy. These trends offer a potential boost of the megamaser detection rates to 6 - 15%, or a factor of 2-8 relative to the current rates, depending on the chosen sample selection criteria, while fostering real chances for discovering >= 20 new megamaser disks.