A Water Maser and Ammonia Survey of GLIMPSE Extended Green Objects (EGOs)

TL;DR

This study surveys 94 massive young stellar objects using water maser and ammonia lines, revealing correlations between maser activity, ammonia emission, and methanol maser associations, supporting their youth and energetic processes.

Contribution

It provides the first comprehensive water maser and ammonia survey of all northern EGOs, analyzing their properties and associations with methanol masers to understand their evolutionary stages.

Findings

High detection rates of ammonia and water masers in EGOs.

EGOs with methanol masers show higher ammonia linewidths and temperatures.

No significant correlation between water maser luminosity and clump density.

Abstract

We present the results of a Nobeyama 45-m water maser and ammonia survey of all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 micron emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and detect emission towards 97%, 63%, and 46% of our sample, respectively (median rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The derived water maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on MIR properties or maser associations. Water masers and warm dense gas, as indicated by emission in the higher-excitation ammonia transitions, are most frequently detected towards EGOs also associated with both Class I and II methanol masers. 95% (81%) of such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of EGOs without either methanol maser type. As populations, EGOs associated with Class I and/or II methanol masers have significantly higher ammonia linewidths, column densities, and kinetic temperatures than EGOs undetected in methanol maser surveys. However, we find no evidence for statistically significant differences in water maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic water maser luminosity and clump number density. Water maser luminosity is weakly correlated with clump (gas) temperature and clump mass.