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

Abstract

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.

arXiv comment37 pages, 13 figures (incl. 2 figure sets), 8 tables (incl. 4 MRTs)

References in corpus (56)

• Embedded Clusters in Molecular Clouds
• The SIMBAD astronomical database
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns
• A Catalog of Extended Green Objects (EGOs) in the GLIMPSE Survey: A new sample of massive young stellar object outflow candidates
• Star formation through gravitational collapse and competitive accretion
• Massive star formation in 100,000 years from turbulent and pressurized molecular clouds
• ATLASGAL --- properties of a complete sample of Galactic clumps
• Predictions for high-frequency radio surveys of extragalactic sources
• A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
• Disk-mediated accretion burst in a high-mass young stellar object
• The Formation of Massive Stars by Accretion Through Trapped Hypercompact HII Regions
• A Magnetized Jet from a Massive Protostar
• The RMS Survey: Ammonia and water maser analysis of massive star forming regions
• An extraordinary outburst in the massive protostellar system NGC6334I-MM1: quadrupling of the millimeter continuum
• The formation of massive stars: accretion, disks and the development of hypercompact HII regions
• The 6-GHz methanol multibeam maser catalogue II: Galactic longitudes 6 to 20
• Radio Jets from Young Stellar Objects
• Hierarchical Cluster Assembly in Globally Collapsing Clouds
• Kinematic Distances: A Monte Carlo Method
• ATLASGAL --- Complete compact source catalogue: 280\degr\ $<\ell <$ 60\degr
• First Science Observations with SOFIA/FORCAST: The FORCAST Mid-infrared Camera
• Methanol and water masers in IRAS 20126+4104: The distance, the disk, and the jet
• A search for ionized jets towards massive young stellar objects
• G11.92-0.61 MM 1: A fragmented Keplerian disk surrounding a proto-O star
• The earliest phases of high-mass star formation, as seen in NGC 6334 by \emph{Herschel}
• The diversity of methanol maser morphologies from VLBI observations
• Physical characteristics of bright Class I methanol masers
• VLBI study of maser kinematics in high-mass SFRs. I. G16.59-0.05
• Infall and outflow within 400 AU from a high-mass protostar. 3-D velocity fields from methanol and water masers in AFLG 5142
• Outflow-Confined H II Regions. I. First Signposts of Massive Star Formation
• VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41
• How can young massive clusters reach their present-day sizes?
• Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: I. VLA Observations
• Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39
• Water maser variability over 20 years in a large sample of star-forming regions: the complete database
• Bipolar HII regions - Morphology and star formation in their vicinity - I - G319.88$+$00.79 and G010.32$-$00.15
• Sub-arcsecond (sub)millimeter imaging of the massive protocluster G358.93-0.03: Discovery of 14 new methanol maser lines associated with a hot core
• Simultaneous low- and high-mass star formation in a massive protocluster: ALMA observations of G11.92-0.61
• A Water Maser and Ammonia Survey of GLIMPSE Extended Green Objects (EGOs)
• Deep Very Large Array Radio Continuum Surveys of GLIMPSE Extended Green Objects (EGOs)
• The Massive Protostellar Cluster NGC6334I at 220 AU Resolution: Discovery of Further Multiplicity, Diversity and a Hot Multi-Core
• Water masers accompanying OH and methanol masers in star formation regions
• Monitoring observations of 6.7 GHz methanol masers
• Investigating the Nature of the Dust Emission around Massive Protostar NGC 7538 IRS 1: Circumstellar Disk and Outflow?
• The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2
• Protostellar Outflows at the EarliesT Stages (POETS). I. Radio thermal jets at high resolution nearby H${}_2$O maser sources
• European VLBI Network imaging of 6.7 GHz methanol masers
• Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: II. The Nature of the Radio Sources
• A Protostellar Jet Emanating from a Hypercompact HII Region
• A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176
• VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
• Testing the Hypothesis that Methanol Maser Rings Trace Circumstellar Disks: High Resolution Near-IR and Mid-IR Imaging
• Protostellar Outflows at the EarliesT Stages (POETS). IV. Statistical properties of the 22 GHz H2O masers
• SOFIA {\it FORCAST} Photometry of 12 Extended Green Objects in the Milky Way
• Radiation hydrodynamic simulations of massive star formation via gravitationally trapped HII regions - Spherically symmetric ionised accretion flows

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