2013ApJ...764...61C

We present the results of a Nobeyama 45 m H₂ O maser and NH₃survey of all 94 northern GLIMPSE extended green objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 µm emission. We observed the NH₃(1,1), (2,2), and (3,3) inversion lines, and detected emission toward 97%, 63%, and 46% of our sample, respectively (median rms ∼ 50 mK). The H₂ O maser detection rate is 68% (median rms ∼ 0.11 Jy). The derived H₂ O 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 mid-infrared (MIR) properties or maser associations. H₂ O masers and warm dense gas, as indicated by emission in the higher-excitation NH₃transitions, are most frequently detected toward EGOs also associated with both Class I and II CH₃ OH masers. Ninety-five percent (81%) of such EGOs are detected in H₂ O (NH₃(3,3)), compared to only 33% (7%) of EGOs without either CH₃ OH maser type. As populations, EGOs associated with Class I and/or II CH₃ OH masers have significantly higher NH₃ line widths, column densities, and kinetic temperatures than EGOs undetected in CH₃ OH maser surveys. However, we find no evidence for statistically significant differences in H₂ O 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 H₂ O maser luminosity and clump number density. H₂O maser luminosity is weakly correlated with clump (gas) temperature and clump mass.