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The extragalactic radio-source population at 95 GHz | | Elaine M. Sadler
; Roberto Ricci
; Ronald D. Ekers
; Robert J. Sault
; Carole A. Jackson
; Gianfranco De Zotti
; | | Date: |
22 Sep 2007 | | Abstract: | We have used the Australia Telescope Compact Array (ATCA) at 95GHz to carry
out continuum observations of 130 extragalactic radio sources selected from the
Australia Telescope 20GHz survey. We use a triple-correlation method to measure
simultaneous 20 and 95 GHz flux densities for these objects, and over 90% of
our target sources are detected at 95 GHz. We show that the ATCA can robustly
measure 95GHz flux densities to ~10% accuracy for sources stronger than ~50mJy.
The 95GHz source population at the flux levels probed by this study is
dominated by QSOs with a median redshift z~1. We find a correlation between
optical magnitude and 95GHz flux density which suggests that many of the
brightest 95 GHz sources are relativistically beamed, with both the optical and
millimetre continuum significantly brightened by Doppler boosting.
For a flux-limited sample of extragalactic sources, we show that the median
20-95GHz spectral index does not vary significantly with flux density for S20
>150 mJy. This allows us to estimate the extragalactic radio source counts at
95GHz by combining our observed 20-95GHz spectral-index distribution with the
accurate 20GHz source counts measured in the AT20G survey.
Our derived 95GHz source counts at flux densities above 80 mJy are
significantly lower than those found by several previous studies. The main
reason is that most radio sources with flat or rising spectra in the frequency
range 5-20GHz show a spectral turnover between 20 and 95 GHz. As a result,
there are fewer 95GHz sources (by almost a factor of two at 0.1 Jy) than would
be predicted on the basis of extrapolation from the source populations seen in
lower-frequency surveys. We also derive the predicted confusion noise in CMB
surveys at 95GHz and find a value 20-30% lower than previous estimates. | | Source: | arXiv, 0709.3563 | | Services: | Forum | Review | PDF | Favorites | |
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