# 84-GHz methanol masers, their relationship to 36-GHz methanol masers and their molecular environments

## TL;DR

This study observes 94 known class I methanol maser sites at 36 and 84 GHz, revealing similar spectral profiles, new detections, and correlations with molecular environments, advancing understanding of maser environments.

## Contribution

First simultaneous observations of 36- and 84-GHz methanol masers across a large sample, identifying new maser sites and analyzing their molecular environment relationships.

## Key findings

- High detection rate of 84-GHz masers, many observed for the first time.
- Similar spectral profiles and flux ratios between 36- and 84-GHz transitions.
- Correlations between maser flux densities and various molecular line intensities.

## Abstract

We present observations of the 36- (4_-1 -> 3_0E) and 84-GHz (5_-1 -> 4_0 E) class I methanol maser transitions towards a sample of 94 known class I sites. These observations resulted in 93 and 92 detections in the 84- and 36-GHz transitions. While the majority of the 36-GHz sources have been previously reported, many of the sites are observed in the 84-GHz transition for the first time. The near-simultaneous observations of the two transitions revealed strikingly similar spectral profiles and a mean and median 36- to 84-GHz integrated flux density ratio of 2.6 and 1.4. Alongside the 36- and 84-GHz observations, we included rare class II methanol masers at 37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz, a number of recombination lines, and thermal molecular transitions. We detect one new site of 86.6- and 86.9-GHz methanol masers, as well as six maser candidates in one or more of 37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz methanol maser transitions. We detect a relatively higher rate of HC3N compared to that reported by MALT90 (once the respective detection limits were taken into account) who targeted dense dust clumps, suggesting that the class I methanol maser targets incorporate a relatively higher number of warm protostellar sources. We further find that there are similar relationships between the integrated flux density of both class I transitions with the integrated intensity of HC3N, HNC, HCO+, HNC, SiO and H13CO+. We suggest that this indicates that the integrated flux density of the 36- and 84-GHz transitions are closely linked to the available gas volume.