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. (arXiv:2110.04270v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Towner_A/0/1/0/all/0/1">A. P. M. Towner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brogan_C/0/1/0/all/0/1">C. L. Brogan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hunter_T/0/1/0/all/0/1">T. R. Hunter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cyganowski_C/0/1/0/all/0/1">C. J. Cyganowski</a>
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$-$0.47 contain 1 to 2 massive
sources based on the presence of methanol maser groups, which is consistent
with our previous work suggesting that these are typical massive protoclusters
in which only one to a few of the YSOs are massive.
We have observed a sample of 9 Extended Green Objects (EGOs) at 1.3 and 5 cm
with the VLA with sub-arcsecond resolution and ~7-14 uJy/beam sensitivities in
order to characterize centimeter continuum emission as it first appears in
these massive protoclusters. We find EGO-associated continuum emission – within
1 arcsec of the extended 4.5 um emission – in every field, which is typically
faint (order 10^1-10^2 uJy) and compact (unresolved at 0.3-0.5 arcsec). The
derived spectral indices of our 36 total detections are consistent with a wide
array of physical processes, including both non-thermal (19% of detections) and
thermal free-free processes (e.g. ionized jets and compact HII regions, 78% of
sample), and warm dust (1 source). We also find EGO-associated 6.7 GHz CH$_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.
http://arxiv.org/icons/sfx.gif
