Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
  We present a sample of 1,483 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
analogues 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 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.
