High-frequency Radio Spectral Energy Distributions and Polarization Fractions of Sources in an Atacama Cosmology Telescope Survey Field

Details High-frequency Radio Spectral Energy Distributions and Polarization Fractions of Sources in an Atacama Cosmology Telescope Survey Field High-frequency Radio Spectral Energy Distributions and Polarization Fractions of Sources in an Atacama Cosmology Telescope Survey Field

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011apj...732...45s&link_type=abstract

The Astrophysical Journal, Volume 732, Issue 1, article id. 45 (2011).

Astronomy and Astrophysics

Astronomy

3

Galaxies: Active, Galaxies: Jets, Radio Continuum: Galaxies

Scientific paper

We present flux densities and polarization percentages of 159 radio galaxies based on nearly simultaneous Very Large Array observations at four frequencies, 4.86, 8.46, 22.46, and 43.34 GHz. This sample is selected from the high-frequency Australia Telescope 20 GHz (AT20G) survey and consists of all sources with flux density S 20 GHz > 40 mJy in an equatorial field of the Atacama Cosmology Telescope (ACT) survey. For a subset of 25 of these sources, we used the Green Bank Telescope (GBT) to obtain 90 GHz data. The goals of this program are: (1) a characterization of the spectra, polarization, and variability of high-frequency-selected radio sources, (2) extrapolating from the few GHz regime to the ~150 GHz regime of the ACT survey, allowing for more accurate removal of the radio source signal in our particular field, and (3) providing a data set that will allow more accurate modeling of the high-frequency radio source contamination in current and future Sunyaev-Zeldovich and cosmic microwave background experiments. We find that, as expected, this sample consists of flatter spectrum and more compact or point-like sources than low-frequency-selected samples. In the K band, variability is typically lsim20%, although there are exceptions. The higher frequency data are well suited to the detection of extreme gigahertz peak spectrum sources. The inclusion of the 43 GHz data causes the relative fraction of inverted spectrum sources to go down and of peaked spectrum sources to go up when compared with the AT20G survey results. The trend largely continues with the inclusion of the 90 GHz data, although ~10% of the sources with GBT data show a spectral upturn from 43 GHz to 90 GHz. The measured polarization fractions are typically <5%, although in some cases they are measured to be up to ~20%. For sources with detected polarized flux in all four bands, about 40% of the sample, the polarization fractions typically increase with frequency. This trend is stronger for steeper spectrum sources as well as for the lower flux density sources.

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