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The GOODS-N Jansky VLA 10 GHz Pilot Survey: Sizes of Star-forming μJY Radio Sources

Murphy, Eric J. and Momjian, Emmanuel and Condon, James J. and Chary, Ranga-Ram and Dickinson, Mark and Inami, Hanae and Taylor, Andrew R. and Weiner, Benjamin J. (2017) The GOODS-N Jansky VLA 10 GHz Pilot Survey: Sizes of Star-forming μJY Radio Sources. Astrophysical Journal, 839 (1). Art. No. 35. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20170411-085858504

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Abstract

Our sensitive (σ_n ≈ 572 nJy beam^(-1)), high-resolution (FWHM θ_(1/2) = 0.”22 ≈ 2 kpc at z ≳ 1), 10 GHz image covering a single Karl G. Jansky Very Large Array (VLA) primary beam (FWHM Θ_(1/2) ≈ 4.’25) in the GOODS-N field contains 32 sources with S_p ≳ 2 µJy beam^(-1) and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is 〈Θ_M〉= 167 ± 32 mas ≈ 1.2 ± 0.28 kpc, with rms scatter ≈ 91 mas ≈ 0.79 kpc. In units of the effective radius r_e that encloses half their flux, these radio sizes are 〈r_e〉≈ 69 ± 13 mas ≈ 509 ± 114 pc, with rms scatter ≈ 38 mas ≈ 324 pc. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected Hα sizes. We made a low-resolution (θ_(1/2) = 1.”0) image with ≈ 10x better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices α^(10 Ghz)_(1.4 Ghz). It contains six new sources with S_p ≳ 3.9 µJy beam^(-1) and OIR counterparts. The median redshift of all 38 sources is 〈z〉= 1.24 ± 0.15. The 19 sources with 1.4 GHz counterparts have a median spectral index of 〈α^(10 Ghz)_(1.4 Ghz)〉= -0.74 ± 0.10, with rms scatter ≈ 0.35. Including upper limits on α for sources not detected at 1.4 GHz flattens the median to 〈α^(10 Ghz)_(1.4 Ghz)〉≳ -0.61, suggesting that the μJy radio sources at higher redshifts—and hence those selected at higher rest-frame frequencies—may have flatter spectra. If the non-thermal spectral index is α_(NT) ≈ -0.85, the median thermal fraction of sources selected at median rest-frame frequency ≈ 20 GHz is ≳ 48%.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aa62fdDOIArticle
http://iopscience.iop.org/article/10.3847/1538-4357/aa62fd/metaPublisherArticle
https://arxiv.org/abs/1702.06963arXivDiscussion Paper
ORCID:
AuthorORCID
Murphy, Eric J.0000-0001-7089-7325
Momjian, Emmanuel0000-0003-3168-5922
Condon, James J.0000-0003-4724-1939
Chary, Ranga-Ram0000-0001-7583-0621
Dickinson, Mark0000-0001-5414-5131
Inami, Hanae0000-0003-4268-0393
Additional Information:© 2017 The American Astronomical Society. Received 2016 August 29; revised 2017 February 21; accepted 2017 February 22; published 2017 April 11. 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. thanks G. Brammer and P. van Dokkum for useful discussions that helped improve this paper. E.J.M. also thanks K. Nyland for helping with figure preparation, D. Riechers for providing unpublished source positions to help prepare these observations, and A. Pope for providing additional data to help with the analysis. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. E.J.M. gratefully acknowledges the hospitality of the Aspen Center for Physics, which is supported by the National Science Foundation Grant No. PHY-1066293.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NSFPHY-1066293
Subject Keywords:galaxies: evolution – galaxies: fundamental parameters – galaxies: high-redshift – galaxies: star formation – radio continuum: general
Issue or Number:1
Record Number:CaltechAUTHORS:20170411-085858504
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170411-085858504
Official Citation:Eric J. Murphy et al 2017 ApJ 839 35
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76501
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:11 Apr 2017 16:52
Last Modified:03 Oct 2019 17:01

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