Pen, Ue-Li and Chang, Tzu-Ching and Hirata, Christopher M. and Peterson, Jeffrey B. and Roy, Jayanta and Gupta, Yashwant and Odegova, Julia and Sigurdson, Kris (2009) The GMRT EoR experiment: limits on polarized sky brightness at 150 MHz. Monthly Notices of the Royal Astronomical Society, 399 (1). pp. 181-194. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20091111-122821538
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The Giant Metrewave Radio Telescope (GMRT) reionization effort aims to map out the large-scale structure of the Universe during the epoch of reionization (EoR). Removal of polarized Galactic emission is a difficult part of any 21 cm EoR programme, and we present new upper limits to diffuse polarized foregrounds at 150 MHz. We find no high-significance evidence of polarized emission in our observed field at mid-galactic latitude (J2000 08^(h)26^(m)+26). We find an upper limit on the two-dimensional angular power spectrum of diffuse polarized foregrounds of (l^(2)C_l/2π)^(1/2) < 3 K in frequency bins of width δν = 1 MHz at 300 < l < 1000 . The three-dimensional power spectrum of polarized emission, which is most directly relevant to EoR observations, is [k^(3)P_(P)(k)/2π^(2)]^(1/2) < 2 K at k⊥ > 0.03 h Mpc^(−1), k < 0.1 h Mpc^(−1). This can be compared to the expected EoR signal in total intensity of [k^(3)P(k)/2π^2]^(1/2) ~ 10 mK . We find that polarized structure is substantially weaker than suggested by extrapolation from higher frequency observations, so the new low upper limits reported here reduce the anticipated impact of these foregrounds on EoR experiments. We discuss the Faraday beam and depth depolarization models and compare predictions of these models to our data. We report on a new technique for polarization calibration using pulsars, as well as a new technique to remove broad-band radio frequency interference. Our data indicate that, on the edges of the main beam at the GMRT, polarization squint creates ~3 per cent leakage of unpolarized power into polarized maps at zero rotation measure. Ionospheric rotation was largely stable during these solar minimum nighttime observations.
|Additional Information:||© 2009 ASIAA. Journal compilation © 2009 RAS. Accepted 2009 April 25. Received 2009 February 18; in original form 2008 July 8. We acknowledge helpful discussions with Ethan Vishniac, Michel Brentjens,MarcAntoine Miville-Deschenes and Judd Bowman.We acknowledge financial support by CIfAR, NSERC and NSF. The GMRT is operated by the National Centre for Radio Astrophysics (NCRA). We thank the NCRA for their extended support in this project.|
|Subject Keywords:||polarization; cosmology: observations; radio continuum: ISM|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||13 Nov 2009 16:47|
|Last Modified:||26 Dec 2012 11:33|
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