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Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

Kapińska, A. D. and Hanish, D. J. (2017) Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies. Astrophysical Journal, 838 (1). Art. No. 68. ISSN 1538-4357.

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We present new radio continuum observations of NGC 253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC 253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free–free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGC 253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC 253 in our radio images. At 154–231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ~8 kpc in the z-direction (from the major axis).

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Additional Information:© 2017 The American Astronomical Society. Received 2016 July 29; revised 2017 January 29; accepted 2017 February 6; published 2017 March 27. A.D.K. thanks P. A. Curran for valuable discussions on data modeling and constant encouragement in achieving the goals. The authors thank the anonymous referee for careful reading of the manuscript and suggestions that improved this paper. The authors thank W. Pietsch and D. Lucero for providing, respectively, X-ray and H i fits images of NGC 253, and O.I. Wong and X. Sun for helpful comments. The authors thank V. Heesen for 1.465 GHz image of NGC 253 and for helpful discussions. S.B. acknowledges funding for the ICRAR Summer Scholarship. This research was conducted under financial support of the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. This scientific work makes use of the Murchison Radio-astronomy Observatory, operated by CSIRO. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. Support for the operation of the MWA is provided by the Australian Government (NCRIS), under a contract to Curtin University administered by Astronomy Australia Limited. We acknowledge the Pawsey Supercomputing Centre, which is supported by the Western Australian and Australian Governments. 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. This publication uses the following radio data reduction software: the Multichannel Image Reconstruction, Image Analysis and Display software (Miriad; Sault et al. 1995), the Common Astronomy Software Applications package (CASA; McMullin et al. 2007), and the Astronomical Image Processing System AIPS. AIPS is produced and maintained by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Australian Research CouncilCE110001020
Subject Keywords:galaxies: halos – galaxies: individual (NGC 253) – galaxies: starburst – radiation mechanisms: nonthermal – radiation mechanisms: thermal – radio continuum: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20170327-124202431
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Official Citation:A. D. Kapińska et al 2017 ApJ 838 68
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75418
Deposited By: Tony Diaz
Deposited On:27 Mar 2017 20:04
Last Modified:03 Oct 2019 16:50

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