Water Masers Associated with Star Formation in the Antennae Galaxies

TL;DR

This study uses high-resolution radio observations to locate water masers in the Antennae Galaxies, revealing their association with star-forming regions and young super star clusters, demonstrating masers as precise markers of star formation.

Contribution

It provides the first detailed high-resolution imaging of water masers in an interacting galaxy, linking masers to young super star clusters and molecular clouds.

Findings

Water masers are associated with massive molecular clouds.

Masers coincide with compact radio sources indicating young star clusters.

Maser regions are obscured in optical/near-IR but visible in radio and Paα emission.

Abstract

We present Very Large Array observations with 80 milliarcsecond resolution (~9 pc) of the recently discovered Galactic-analog water masers in the Antennae interacting galaxies (NGC 4038/NGC 4039; Arp244). Three regions of water maser emission are detected: two in the ``interaction region'' (IAR) and the third ~5.6'' (> 600 pc) west of the NGC 4039 nucleus. The isotropic water maser luminosities range from 1.3 to 7.7 L_sun. All three maser regions are mostly obscured in the optical/near-infrared continuum, and are coincident with massive CO-identified molecular clouds. The water maser velocities are in excellent agreement with those of the molecular gas. We also present archival VLA 3.6 cm data with ~0.28" (~30 pc) and ~0.8" (~90 pc) resolution toward the maser locations. All three maser regions are coincident with compact 3.6 cm radio continuum emission, and two are dominated by thermal ionized gas, suggesting the presence of natal super star clusters containing the equivalent of a few thousand O stars. We also present detailed comparisons between the radio data and existing HST ACS (optical) and NICMOS (near-IR) data and find that both maser regions in the IAR are also associated with Pa\alpha emission and neither source is detected shortward of 2 microns. These results highlight the potential of using Galactic-analog water masers to pinpoint sites of young super star cluster formation with exquisite angular resolution.