Water Masers in the Andromeda Galaxy: The First Step Toward Proper Motion

TL;DR

This study detected water masers in M31 to enable precise proper motion and distance measurements, crucial for understanding Local Group dynamics and dark matter profiles, with potential for rapid and long-term observations.

Contribution

First detection of water masers in M31 suitable for proper motion studies, providing a new method to measure galaxy dynamics and distance with high precision.

Findings

Detected five water masers in M31 using the Green Bank Telescope.

Masers are distributed around the molecular ring, ideal for proper motion measurements.

No correlation found between IR luminosity and maser luminosity, indicating unpredictable maser brightness.

Abstract

We have detected and confirmed five water maser complexes in the Andromeda Galaxy (M31) using the Green Bank Telescope. These masers will provide the high brightness temperature point sources needed for proper motion studies of M31, enabling measurement of its full three-dimensional velocity vector and its geometric distance via proper rotation. The motion of M31 is the keystone of Local Group dynamics and a gateway to the dark matter profiles of galaxies in general. Our survey for water masers selected 206 luminous compact 24 micron-emitting regions in M31 and was sensitive enough to detect any maser useful for ~10 microarcsecond per year astrometry. The newly discovered masers span the isotropic luminosity range 0.3-1.9 x 10^-3 L(Sun) in single spectral components and are analogous to luminous Galactic masers. The masers are distributed around the molecular ring, including locations close to the major and minor axes, which is nearly ideal for proper motion studies. We find no correlation between 24 micron luminosity and water maser luminosity, suggesting that while water masers arise in star-forming regions, the nonlinear amplification pathways and beamed nature of the water masers means that they are not predictable based on IR luminosity alone. This suggests that there are additional bright masers to be found in M31. We predict that the geometric distance and systemic proper motion of M31 can be measured in 2-3 years with current facilities. A "moving cluster" observation of diverging masers as M31 approaches the Galaxy may be possible in the long term.