Sardinia Radio Telescope observations of Local Group dwarf galaxies -- I. The cases of NGC6822, IC1613, and WLM

TL;DR

This study used the Sardinia Radio Telescope to search for water and methanol masers in three Local Group dwarf galaxies, mapping their radio continuum and spectral lines to understand their star formation and dynamics.

Contribution

First deep radio continuum and spectral line maps of NGC6822, IC1613, and WLM, providing insights into star formation rates and maser emission in these galaxies.

Findings

No methanol or water masers detected, consistent with low SFRs and metallicities.

Star formation rates derived from radio continuum are lower than other wavelengths.

Radio continuum maps reveal star forming regions and global SFRs.

Abstract

Almost all dwarf galaxies in the Local Group that are not satellites of the Milky Way or M31, belong to either one of two highly-symmetric planes. It is still a matter of debate, whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to discriminate between these scenarios. Such motions could be determined with multi-epoch Very Long Baseline Interferometry (VLBI) of sources that show emission from water and methanol at frequencies of 22 and 6.7 GHz, respectively. We report searches for such masers. We have mapped three Local Group galaxies, NGC6822, IC1613 and WLM in the bands covering the water vapor and methanol lines. These systems are members of the two above mentioned planes of galaxies. We have produced deep radio continuum (RC) maps and spectral line cubes. The former have been used to identify star forming regions and to derive global galactic star formation rates (SFRs). These SFRs turn out to be lower than those determined at other wavelengths in two of our sources. This indicates that dwarf galaxies may follow predictions on the RC-SFR relation only in individual regions of enhanced radio continuum emission, but not when considering the entire optical body of the sources. No methanol or water maser emission has been confidently detected, down to line luminosity limits of ~0.004 and 0.01 solar luminosities, respectively. This finding is consistent with the small sizes, low SFRs and metallicities of these galaxies.