VLA Observations of 9 Extended Green Objects in the Milky Way: Ubiquitous Weak, Compact Continuum Emission, and Multi-Epoch Emission from CH$_3$OH, H$_2$O, and NH$_3$ Masers
| Autor: | Towner, A. P. M., Brogan, C. L., Hunter, T. R., Cyganowski, C. J. |
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| Rok vydání: | 2021 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/1538-4357/ac2c86 |
| Popis: | We have observed a sample of 9 Extended Green Objects (EGOs) at 1.3 and 5 cm with the VLA with sub-arcsecond resolution and ~7-14 uJy/beam sensitivities in order to characterize centimeter continuum emission as it first appears in these massive protoclusters. We find EGO-associated continuum emission - within 1 arcsec of the extended 4.5 um emission - in every field, which is typically faint (order 10^1-10^2 uJy) and compact (unresolved at 0.3-0.5 arcsec). The derived spectral indices of our 36 total detections are consistent with a wide array of physical processes, including both non-thermal (19% of detections) and thermal free-free processes (e.g. ionized jets and compact HII regions, 78% of sample), and warm dust (1 source). We also find EGO-associated 6.7 GHz CH$_3$OH and 22 GHz H$_2$O maser emission in 100% of the sample, and NH$_3$ (3,3) masers in ~45%; we do not detect any NH$_3$ (6,6) masers at ~5.6 mJy/beam sensitivity. We find statistically-significant correlations between radio-distance and bolometric luminosities at two physical scales and three frequencies, consistent with thermal emission from ionized jets, but no correlation between water-maser and radio-distance luminosities for our sample. From these data, we conclude that EGOs likely host multiple different centimeter continuum-producing processes simultaneously. Additionally, at our ~1000 au resolution, we find that all EGOs except G18.89$-$0.47 contain 1 to 2 massive sources based on the presence of methanol maser groups, which is consistent with our previous work suggesting that these are typical massive protoclusters in which only one to a few of the YSOs are massive. Comment: 37 pages, 13 figures (incl. 2 figure sets), 8 tables (incl. 4 MRTs) |
| Databáze: | arXiv |
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