Foregrounds for redshifted 21cm studies of reionization: Giant Meter Wave Radio Telescope 153MHz observations
Abstract
Foreground subtraction is the biggest challenge for future redshifted 21cm observations to probe reionization. We use a short Giant Meter Wave Radio Telescope (GMRT) observation at 153MHz to characterize the statistical properties of the background radiation across ~1° to subarcmin angular scales, and across a frequency band of 5MHz with 62.5kHz resolution. The statistic we use is the visibility correlation function, or equivalently the angular power spectrum C_{l}. We present the results obtained from using relatively unsophisticated, conventional data calibration procedures. We find that even fairly simpleminded calibration allows one to estimate the visibility correlation function at a given frequency V_{2}(U, 0). From our observations, we find that V_{2}(U, 0) is consistent with foreground model predictions at all angular scales except the largest ones probed by our observations where the model predictions are somewhat in excess. On the other hand, the visibility correlation between different frequencies κ(U, ∆ν) seems to be much more sensitive to calibration errors. We find a rapid decline in κ(U, ∆ν), in contrast with the prediction of less than 1 per cent variation across 2.5MHz. In this case, however, it seems likely that a substantial part of the discrepancy may be due to limitations of data reduction procedures.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2008
 DOI:
 10.1111/j.13652966.2008.12984.x
 arXiv:
 arXiv:0801.2424
 Bibcode:
 2008MNRAS.385.2166A
 Keywords:

 methods: statistical;
 cosmology: observations;
 diffuse radiation;
 Astrophysics
 EPrint:
 10 pages, 7 figures, 1 table, Accepted for Publication in MNRAS