Title:	Extragalactic peaked-spectrum radio sources at low frequencies
Authors:	Callingham, J.R. Ekers, R.D. Gaensler, B.M. Dwarakanath, K.S. +20 Co-authors
Issue Date:	20-Feb-2017
Publisher:	IOP Sciences for The American Astronomical Society
Citation:	The Astrophysical Journal, 2017, Vol.836, p174
Abstract:	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.
Description:	Open Access
URI:	http://hdl.handle.net/2289/6697
ISSN:	0004-637X 1538-4357-(Online)
Alternative Location:	http://adsabs.harvard.edu/abs/2017ApJ...836..174C https://arxiv.org/abs/1701.02771 http://dx.doi.org/10.3847/1538-4357/836/2/174
Copyright:	2017, The American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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