A sensitive search for predicted methanol maser transitions with the Australia Telescope Compact Array

TL;DR

This study used the ATCA to search for predicted methanol maser emissions in star formation regions but found no detections, setting upper limits that support current maser models and highlighting the need for more sensitive future observations.

Contribution

The paper provides the first sensitive upper limits on specific methanol maser transitions in high-mass star formation regions using high-resolution ATCA observations.

Findings

No methanol maser emission detected in targeted transitions.

Upper limit of ~1300K on brightness temperature for these transitions.

Results support existing models of class II methanol masers.

Abstract

We have used the Australia Telescope Compact Array (ATCA) to search for a number of centimetre wavelength methanol transitions which are predicted to show weak maser emission towards star formation regions. Sensitive, high spatial and spectral resolution observations towards four high-mass star formation regions which show emission in a large number of class II methanol maser transitions did not result in any detections. From these observations we are able to place an upper limit of <~1300K on the brightness temperature of any emission from the $3_1$A$^+$-$3_1$A$^-$, $17_{-2}$-$18_{-3}$E ($v_t=1$), $12_4$-$13_3$A$^-$, $12_4$-$13_3$A$^+$ and $4_1$A$^+$-$4_1$A$^-$ transitions of methanol in these sources on angular scales of 2 arcseconds. This upper limit is consistent with current models for class II methanol masers in high-mass star formation regions and better constraints than those provided here will likely require observations with next-generation radio telescopes.