Ubiquitous Water Masers in Nearby Star-Forming Galaxies

TL;DR

This study reports a 100% detection rate of water masers in four nearby star-forming galaxies, indicating that such masers are likely very common in starburst galaxies and related to regions of intense star formation.

Contribution

It demonstrates that water masers are prevalent in nearby star-forming galaxies and suggests previous detection limitations were due to insufficient sensitivity.

Findings

All detected masers are associated with known star-forming regions.

Detected maser luminosities are comparable to Galactic massive star-forming regions.

High detection rate implies water masers are common in starburst galaxies.

Abstract

We report the detection of water maser emission from four nearby galaxies hosting ultradense HII (UDHII) regions, He 2-10, the Antennae galaxies (NGC 4038/4039), NGC 4214, and NGC 5253, with the Green Bank Telescope. Our detection rate is 100%, and all of these H2O "kilomasers" (L(H2O) < 10 L_sun) are located toward regions of known star formation as traced by UDHII regions and bright 24 micron emission. Some of the newly discovered H2O masers have luminosities 1-2 orders of magnitude less than previous extragalactic studies and the same order of magnitude as those typical of Galactic massive star-forming regions. The unusual success of this minisurvey suggests that H2O maser emission may be very common in starburst galaxies, and the paucity of detections to date is due to a lack of sufficient sensitivity. While the galaxy sample was selected by the presence of UDHII regions, and the UDHII regions lie within the telescope beam, in the absence of H2O spectral line maps the connection between H2O masers and UDHII regions has not yet been demonstrated.