Search for Class I methanol masers in low-mass star formation regions

TL;DR

This study conducted a survey for class I methanol masers in low-mass star formation regions, detecting weak masers in select sources and establishing their properties and prevalence compared to high-mass regions.

Contribution

It provides the first systematic search for class I methanol masers in low-mass star formation regions and characterizes their luminosities and occurrence.

Findings

Detected weak masers in four sources at 44 and 36 GHz.

No significant variability observed over multiple years.

Masers are associated with higher methanol column densities.

Abstract

A survey of young bipolar outflows in regions of low-to-intermediate-mass star formation has been carried out in two class I methanol maser transitions: 7_0-6_1A+ at 44 GHz and 4_{-1}-3_0E at 36 GHz. We detected narrow features towards NGC 1333I2A, NGC 1333I4A, HH25MMS, and L1157 at 44 GHz, and towards NGC 2023 at 36 GHz. Flux densities of the lines detected at 44 GHz are no higher than 11 Jy and the relevant source luminosities are about 10^{22} erg s{-1}, which is much lower than those of strong masers in high-mass star formation regions. No emission was found towards 39 outflows. All masers detected at 44 GHz are located in clouds with methanol column densities of the order of or larger than a few x 10^{14} cm$^{-2}. The upper limits for the non-detections are typically of the order of 3--5 Jy. Observations in 2004, 2006, and 2008 did not reveal any significant variability of the 44 GHz masers in NGC 1333I4A, HH25MMS, and L1157.