Precise Positions of Methanol Masers

TL;DR

This paper presents a catalog of over 350 methanol maser sites with sub-arcsecond positional accuracy, enabling detailed comparisons with other star formation tracers and revealing new insights into maser distributions.

Contribution

The study provides the most precise methanol maser positions to date, improving accuracy by a factor of ten and clarifying associations with OH masers and infrared sources.

Findings

Over 80% of OH masers have coincident methanol masers.

Many sources are newly discovered or have refined positions.

Velocity ranges at individual sites are often smaller than previously thought.

Abstract

The Australia Telescope Compact Array (ATCA) has been used to determine positions for many southern methanol maser sites, with accuracy better than 1 arcsec. The results are presented here as a catalogue of more than 350 distinct sites, some of them new discoveries, and many others with positional precision 10 times better than existing published values. Clusters of 2 or 3 sites are occasionally found to account for single previously listed sources. This in turn reveals that the velocity range for each individual site is sometimes smaller than that of the originally tabulated (blended) source. Only a handful of examples then remain with a velocity range of more than 16 km/s at a single compact (less than 2 arcsec) site. The precise methanol positions now allow apparent coincidences with OH masers to be confidently accepted or rejected; this has led to the important conclusion that, where a 1665-MHz OH maser lies in a massive star formation region, at more than 80 percent of the OH sites there is a precisely coincident methanol maser. The methanol precision achieved here will also allow clear comparisons with likely associated IR sources when the next generation of far-IR surveys produce precise positions.