Extragalactic Peaked-spectrum Radio Sources at Low Frequencies

J.R. Callingham, R.D. Ekers, B.M. Gaensler, J. L B Line, N. Hurley-Walker, E.M. Sadler, S. J. Tingay, P. J. Hancock, M. E. Bell, K.S. Dwarakanath, B. Q. For, T.M.O. Franzen, L. Hindson, M. Johnston-Hollitt, Anna Kapinska, E. Lenc, B. Mckinley, J. Morgan, A.R. Offringa, P. ProcopioL. Staveley-Smith, R.B. Wayth, C. Wu, Q. Zheng

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We present a sample of 1483 sources that display spectral peaks between 72 MHz and 1.4 GHz, selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The GLEAM survey is the widest fractional bandwidth all-sky survey to date, ideal for identifying peaked-spectrum sources at low radio frequencies. Our peaked-spectrum sources are the low-frequency analogs of gigahertz-peaked spectrum (GPS) and compact-steep spectrum (CSS) sources, which have been hypothesized to be the precursors to massive radio galaxies. Our sample more than doubles the number of known peaked-spectrum candidates, and 95% of our sample have a newly characterized spectral peak. We highlight that some GPS sources peaking above 5 GHz have had multiple epochs of nuclear activity, and we demonstrate the possibility of identifying high-redshift (z > 2) galaxies via steep optically thin spectral indices and low observed peak frequencies. The distribution of the optically thick spectral indices of our sample is consistent with past GPS/CSS samples but with a large dispersion, suggesting that the spectral peak is a product of an inhomogeneous environment that is individualistic. We find no dependence of observed peak frequency with redshift, consistent with the peaked-spectrum sample comprising both local CSS sources and high-redshift GPS sources. The 5 GHz luminosity distribution lacks the brightest GPS and CSS sources of previous samples, implying that a convolution of source evolution and redshift influences the type of peaked-spectrum sources identified below 1 GHz. Finally, we discuss sources with optically thick spectral indices that exceed the synchrotron self-absorption limit.

Original languageEnglish
Article number174
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 20 Feb 2017

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    Callingham, J. R., Ekers, R. D., Gaensler, B. M., Line, J. L. B., Hurley-Walker, N., Sadler, E. M., Tingay, S. J., Hancock, P. J., Bell, M. E., Dwarakanath, K. S., For, B. Q., Franzen, T. M. O., Hindson, L., Johnston-Hollitt, M., Kapinska, A., Lenc, E., Mckinley, B., Morgan, J., Offringa, A. R., ... Zheng, Q. (2017). Extragalactic Peaked-spectrum Radio Sources at Low Frequencies. The Astrophysical Journal, 836(2), [174]. https://doi.org/10.3847/1538-4357/836/2/174