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Deep Very Large Array Radio Continuum Surveys of GLIMPSE Extended Green Objects (EGOs) | | C.J. Cyganowski
; C.L. Brogan
; T.R. Hunter
; E. Churchwell
; | | Date: |
8 Sep 2011 | | Abstract: | We present the results of deep, high angular resolution Very Large Array
(VLA) surveys for radio continuum emission towards a sample of 14 GLIMPSE
Extended Green Objects (EGOs). Identified as massive young stellar object
(MYSO) outflow candidates based on their extended 4.5 micron emission in
Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz
Class II and/or 44 GHz Class I methanol masers. No continuum is detected at 3.6
or 1.3 cm towards the majority (57%) of our targets (median rms ~0.03 and 0.25
mJy/beam). Only two EGOs are associated with optically thin emission consistent
with ultracompact/compact HII regions. Both of these sources exhibit
cm-wavelength multiplicity, with evidence that one of the less-evolved members
may be driving the 4.5 micron outflow. Most of the other cm-wavelength EGO
counterparts are weak (< 1 mJy), unresolved, undetected at 1.3 cm, and
characterized by intermediate spectral indices consistent with hypercompact
(HC) HII regions or ionized winds or jets. One EGO cm counterpart, likely an
optically thick HC HII region, is detected only at 1.3 cm and is associated
with hot core line emission and water and 6.7 GHz methanol masers. The results
of our exceptionally sensitive survey indicate that EGOs signify an early stage
of massive star formation, before photoionizing feedback from the central MYSO
significantly influences the (proto)cluster environment. Actively driving
outflows (and so, presumably, actively accreting), the surveyed EGOs are
associated with significant clump-scale gas reservoirs, providing sufficient
material for sustained, rapid accretion. | | Source: | arXiv, 1109.1829 | | Services: | Forum | Review | PDF | Favorites | |
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