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Star Formation in Radio Survey: 3–33 GHz Imaging of Nearby Galaxy Nuclei and Extranuclear Star-forming Regions

Linden, S. T. and Murphy, E. J. and Dong, D. and Momjian, E. and Kennicutt, R. C., Jr. and Meier, D. S. and Schinnerer, E. and Turner, J. L. (2020) Star Formation in Radio Survey: 3–33 GHz Imaging of Nearby Galaxy Nuclei and Extranuclear Star-forming Regions. Astrophysical Journal Supplement Series, 248 (2). Art. No. 25. ISSN 1538-4365.

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We present 3, 15, and 33 GHz imaging toward galaxy nuclei and extranuclear star-forming regions using the Karl G. Jansky Very Large Array as part of the Star Formation in Radio Survey. With 3–33 GHz radio spectra, we measured the spectral indices and corresponding thermal (free–free) emission fractions for a sample of 335 discrete regions having significant detections in at least two radio bands. After removing 14 likely background galaxies, we find that the median thermal fraction at 33 GHz is 92% ± 0.8% with a median absolute deviation of 11%, when a two-component power-law model is adopted to fit the radio spectrum. Limiting the sample to 238 sources that are confidently identified as star-forming regions and not affected by potential AGN contamination (i.e., having galactocentric radii r_G ≥ 250 pc) results in a median thermal fraction of 93% ± 0.8% with a median absolute deviation of 10%. We further measure the thermal fraction at 33 GHz for 163 regions identified at 7'' resolution to be 94% ± 0.8% with a median absolute deviation of 8%. Together, these results confirm that free–free emission dominates the radio spectra of star-forming regions on scales up to ~500 pc in normal star-forming galaxies. We additionally find a factor of ~1.6 increase in the scatter of the measured spectral index and thermal fraction distributions as a function of decreasing galactocentric radius. This trend is likely reflective of the continuous star formation activity occurring in the galaxy centers, resulting in a larger contribution of diffuse nonthermal emission relative to star-forming regions in the disk.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Linden, S. T.0000-0002-1000-6081
Murphy, E. J.0000-0001-7089-7325
Dong, D.0000-0001-9584-2531
Momjian, E.0000-0003-3168-5922
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:© 2020 The American Astronomical Society. Received 2020 February 10; revised 2020 March 20; accepted 2020 April 15; published 2020 May 28. S.T.L. was supported by the NRAO Grote Reber Dissertation Fellowship. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
National Radio Astronomy ObservatoryUNSPECIFIED
Subject Keywords:Star formation ; H II regions; Radio continuum emission ; Star-forming regions ; Radio interferometry ; Radio astronomy ; Galaxies ; Galaxy evolution ; Spiral galaxies ; Extragalactic radio sources
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Star formation (1569); H II regions (694); Radio continuum emission (1340); Star forming regions (1565); Radio interferometry (1346); Radio astronomy (1338); Galaxies (573); Galaxy evolution (594)
Record Number:CaltechAUTHORS:20200528-133209135
Persistent URL:
Official Citation:S. T. Linden et al 2020 ApJS 248 25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103523
Deposited By: Tony Diaz
Deposited On:28 May 2020 20:39
Last Modified:28 May 2020 20:39

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