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

A. D. Kapińska, L. Staveley-Smith, R. Crocker, G. R. Meurer, S. Bhandari, N. Hurley-Walker, A. R. Offringa, D. J. Hanish, N. Seymour, R. D. Ekers, M. E. Bell, J. R. Callingham, K. S. Dwarakanath, B. Q. For, B. M. Gaensler, P. J. Hancock, L. Hindson, M. Johnston-Hollitt, E. Lenc, B. McKinleyJ. Morgan, P. Procopio, R. B. Wayth, C. Wu, Q. Zheng, N. Barry, A. P. Beardsley, Judd Bowman, F. Briggs, P. Carroll, J. S. Dillon, A. Ewall-Wice, L. Feng, L. J. Greenhill, B. J. Hazelton, J. N. Hewitt, D. J. Jacobs, H. S. Kim, P. Kittiwisit, J. Line, A. Loeb, D. A. Mitchell, M. F. Morales, A. R. Neben, S. Paul, B. Pindor, J. C. Pober, J. Riding, S. K. Sethi, N. Udaya Shankar, R. Subrahmanyan, I. S. Sullivan, M. Tegmark, N. Thyagarajan, S. J. Tingay, C. M. Trott, R. L. Webster, S. B. Wyithe, R. J. Cappallo, A. A. Deshpande, D. L. Kaplan, C. J. Lonsdale, S. R. McWhirter, E. Morgan, D. Oberoi, S. M. Ord, T. Prabu, K. S. Srivani, A. Williams, C. L. Williams

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


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).

Original languageEnglish (US)
Article number68
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 20 2017


  • galaxies: halos
  • galaxies: individual (NGC 253)
  • galaxies: starburst
  • radiation mechanisms: nonthermal
  • radiation mechanisms: thermal
  • radio continuum: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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