VLA observations of nine extended green objects in the Milky Way : ubiquitous weak, compact continuum emission, and multi-epoch emission from methanol, water, and ammonia masers
MetadataShow full item record
Altmetrics Handle Statistics
Altmetrics DOI Statistics
We have observed a sample of nine Extended Green Objects (EGOs) at 1.3 and 5 cm with the Very Large Array (VLA) with subarcsecond resolution and ∼7–14 μJy beam−1-sensitivities in order to characterize centimeter continuum emission as it first appears in these massive protoclusters. We find an EGO-associated continuum emission—within 1'' of the extended 4.5 μm emission—in every field, which is typically faint (order 101–102 μJy) and compact (unresolved at 0''.3–0''.5). 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 H ii regions, 78% of sample) and warm dust (1 source). We also find an EGO-associated 6.7 GHz CH3OH and 22 GHz H2O maser emission in 100% of the sample and a NH3 (3,3) masers in ∼45%; we do not detect any NH3 (6,6) masers at ∼5.6 mJy beam−1 sensitivity. We find statistically-significant correlations between Lradio and Lbol at two physical scales and three frequencies, consistent with thermal emission from ionized jets, but no correlation between LH20 and Lradio 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 ∼ 2 massive sources based on the presence of CH3OH 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 young stellar objects are massive.
Towner , APM , Brogan , CL , Hunter , TR & Cyganowski , CJ 2021 , ' VLA observations of nine extended green objects in the Milky Way : ubiquitous weak, compact continuum emission, and multi-epoch emission from methanol, water, and ammonia masers ' , Astrophysical Journal , vol. 923 , no. 2 , 263 . https://doi.org/10.3847/1538-4357/ac2c86
Copyright © 2021 American Astronomical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.3847/1538-4357/ac2c86.
DescriptionSupport for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. Support for this work was provided by the NSF through award SOSP18A-007 from the NRAO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under agreement by the Associated Universities, Inc.
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.