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Excess in the High-frequency Radio Background: Insights from Planck

Murphy, Eric J. and Chary, Ranga-Ram (2018) Excess in the High-frequency Radio Background: Insights from Planck. Astrophysical Journal, 861 (1). Art. No. 27. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20180627-154715302

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Abstract

We conduct a stacking analysis using the combination of 1.4 GHz detections in the NRAO VLA Sky Survey (NVSS) and Planck all-sky maps to estimate the differential source counts down to the few 100 μJy level at 30, 44, 70, and 100 GHz. Using these source count estimates, we are able to measure the integrated extragalactic background light from discrete sources at these frequencies for comparison with the fit to the total radio sky measurements from ARCADE 2. By integrating down to a 1.4 GHz flux density of ≈2 μJy, we measure integrated, extragalactic brightness temperatures from discrete sources of 105.63 ± 10.56 mK, 21.76 ± 3.09 μK, 8.80 ± 0.95 μK, 2.59 ± 0.27 μK, and 1.15 ± 0.10 μk at 1.4, 30, 44, 70, and 100 GHz, respectively. Our measurement at 1.4 GHz is slightly larger than previous measurements, most likely due to using NVSS data compared with older interferometric data in the literature, but it still remains a factor of ≈4.5 below that required to account for the excess extragalactic sky brightness measured at 1.4 GHz by ARCADE 2. The fit to ARCADE 2 total extragalactic sky brightness measurements is also a factor of ≈8.6, 6.6, 6.2, and 4.9 times brighter than what we estimate from discrete sources at 30, 44, 70, and 100 GHz, respectively. The extragalactic sky spectrum (i.e., T_b ∝ ν^β ) from discrete sources appears to flatten with increasing frequency, having a spectral index of β = −2.82 ± 0.06 between 1.4 and 30 GHz, flattening to β = −2.39 ± 0.12 between 30 and 100 GHz. We estimate that the spectral flattening most likely arises from a combination of gigahertz-peaked sources and the hardening of the spectra of radio-detected sources at higher frequencies, particularly at faint flux densities. However, the precise origin of a hard component of energetic electrons responsible for the emission remains unclear.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aac2b6DOIArticle
http://arxiv.org/abs/1805.02672arXivDiscussion Paper
ORCID:
AuthorORCID
Murphy, Eric J.0000-0001-7089-7325
Chary, Ranga-Ram0000-0001-7583-0621
Additional Information:© 2018. The American Astronomical Society. Received 2018 January 4; revised 2018 April 20; accepted 2018 May 2; published 2018 June 27. We thank the anonymous referee for very useful comments that helped to improve the content and presentation of this paper. E.J.M. thanks J.J. Condon for many useful discussions that helped improve the presentation of the paper. E.J.M. also thanks B. Rusholme for providing modified software that significantly sped up the analysis of this investigation, E. Storm for providing her DM annihilation spectra for this study, and B. Mason and C. Sarazin for helpful discussions on cluster radio emission. The results of this paper are based on observations obtained with Planck, an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada. 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), as well as the NASA/ IPAC Infrared Science Archive, both of which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
ESA Member StatesUNSPECIFIED
NASA/JPL/CaltechUNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
NSFUNSPECIFIED
Subject Keywords:cosmic background radiation; cosmology: observations; galaxies: statistics; radio continuum: galaxies; surveys
Record Number:CaltechAUTHORS:20180627-154715302
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180627-154715302
Official Citation:Eric J. Murphy and Ranga-Ram Chary 2018 ApJ 861 27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87421
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:27 Jun 2018 23:14
Last Modified:27 Jun 2018 23:14

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