The Discovery of Water Maser Emission from Eight Nearby Galaxies

TL;DR

This study used the Green Bank Telescope to discover water maser emissions in eight nearby galaxies, revealing new AGN activity and potential for precise distance measurements.

Contribution

First detection of water masers in eight nearby galaxies, including a disk maser in UGC 3789, indicating hidden AGNs and enabling future geometric distance measurements.

Findings

Detected eight new water masers in nearby galaxies.

Identified a disk maser in UGC 3789 indicative of an AGN.

Measured accelerations of systemic features ranging from 2 to 8 km/s/yr.

Abstract

Using the Green Bank Telescope, we conducted a ``snapshot'' survey for water maser emission toward the nuclei of 611 galaxies and detected eight new sources. The sample consisted of nearby (v < 5000 km/s) and luminous (M_B < -19.5) galaxies, some with known nuclear activity but most not previously known to host AGNs. Our detections include both megamasers associated with AGNs and relatively low luminosity masers probably associated with star formation. The detection in UGC 3789 is particularly intriguing because the spectrum shows both systemic and high-velocity lines indicative of emission from an AGN accretion disk seen edge-on. Based on six months of monitoring, we detected accelerations among the systemic features ranging from 2 to 8 km/s/yr, the larger values belonging to the most redshifted systemic components. High-velocity maser lines in UGC 3789 show no detectable drift over the same period. Although UGC 3789 was not known to be an AGN prior to this survey, the presence of a disk maser is strong evidence for nuclear activity, and an optical spectrum obtained later has confirmed it. With follow up observations, it may be possible to measure a geometric distance to UGC 3789.