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The Star Formation in Radio Survey: Jansky Very Large Array 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-forming Regions

Murphy, E. J. and Dong, Dillon and Momjian, E. and Linden, S. and Kennicutt, R. C., Jr. and Meier, D. S. and Schinnerer, E. and Turner, J. L. (2018) The Star Formation in Radio Survey: Jansky Very Large Array 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-forming Regions. Astrophysical Journal Supplement Series, 234 (2). Art. No. 24. ISSN 1538-4365. doi:10.3847/1538-4365/aa99d7.

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We present 33 GHz imaging for 112 pointings toward galaxy nuclei and extranuclear star-forming regions at ≈2" resolution using the Karl G. Jansky Very Large Array (VLA) as part of the Star Formation in Radio Survey. A comparison with 33 GHz Robert C. Byrd Green Bank Telescope single-dish observations indicates that the interferometric VLA observations recover 78% ± 4% of the total flux density over 25" regions (≈kpc scales) among all fields. On these scales, the emission being resolved out is most likely diffuse non-thermal synchrotron emission. Consequently, on the ≈30–300 pc scales sampled by our VLA observations, the bulk of the 33 GHz emission is recovered and primarily powered by free–free emission from discrete H ii regions, making it an excellent tracer of massive star formation. Of the 225 discrete regions used for aperture photometry, 162 are extranuclear (i.e., having galactocentric radii r_G ≥ 250 pc) and detected at >3σ significance at 33 GHz and in Hα. Assuming a typical 33 GHz thermal fraction of 90%, the ratio of optically-thin 33 GHz to uncorrected Hα star formation rates indicates a median extinction value on ≈30–300 pc scales of A Hα ≈ 1.26 ± 0.09 mag, with an associated median absolute deviation of 0.87 mag. We find that 10% of these sources are "highly embedded" (i.e., A Hα gsim 3.3 mag), suggesting that on average, H ii regions remain embedded for lesssim1 Myr. Finally, we find the median 33 GHz continuum-to-Hα line flux ratio to be statistically larger within r G < 250 pc relative to the outer disk regions by a factor of 1.82 ± 0.39, while the ratio of 33 GHz to 24 μm flux densities is lower by a factor of 0.45 ± 0.08, which may suggest increased extinction in the central regions.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Murphy, E. J.0000-0001-7089-7325
Dong, Dillon0000-0001-9584-2531
Momjian, E.0000-0003-3168-5922
Linden, S.0000-0002-1000-6081
Kennicutt, R. C., Jr.0000-0001-5448-1821
Meier, D. S.0000-0001-9436-9471
Schinnerer, E.0000-0002-3933-7677
Turner, J. L.0000-0003-4625-2951
Additional Information:© 2018 American Astronomical Society. Received 2017 August 3. Accepted 2017 November 8. Published 2018 February 1. We would like to thank the anonymous referee for very useful comments that helped to improve the content and presentation of this paper. E.J.M. acknowledges the hospitality of the Aspen Center for Physics, which is supported by National Science Foundation grant No. PHY-1066293. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research made use of APLpy, an open-source plotting package for Python hosted at
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: nuclei; H ii regions; radio continuum: general; stars: formation
Issue or Number:2
Record Number:CaltechAUTHORS:20180202-092413954
Persistent URL:
Official Citation:E. J. Murphy et al 2018 ApJS 234 24
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84650
Deposited By: Ruth Sustaita
Deposited On:02 Feb 2018 17:42
Last Modified:15 Nov 2021 20:21

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