First Constraints on the Global Redshifted 21 cm Background During the Epoch of Reionziation

Details First Constraints on the Global Redshifted 21 cm Background During the Epoch of Reionziation First Constraints on the Global Redshifted 21 cm Background During the Epoch of Reionziation

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21111906b&link_type=abstract

American Astronomical Society, AAS Meeting #211, #119.06; Bulletin of the American Astronomical Society, Vol. 39, p.949

Astronomy and Astrophysics

Astronomy

Scientific paper

We constrain the spectral smoothness of the all-sky mean brightness temperature between 100 and 200 MHz to an instrumental limit of 75 mK (rms) on scales below approximately 10 MHz. From the observations, we place an initial upper limit of 450 mK on the relative brightness temperature of the redshifted 21 cm contribution to the spectrum due to neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization, assuming a rapid transition from a fully neutral to a fully ionized IGM at a redshift of z = 8. This limit is roughly an order of magnitude greater than the 25 to 35 mK expected contribution. Galactic synchrotron emission is the dominate component of the brightness temperature at low radio frequencies and yields an overall power-law-like profile with frequency. Determining the redshifted 21 cm contribution to the radio spectrum requires separating the signal from this foreground spectrum at better than 1 part in 10,000. We employ a simple technique of fitting a low-order polynomial to the spectrum measured by a single dipole antenna system to remove the smooth foreground component. Residuals from the polynomial fit are compared to a model to establish a limit on the magnitude of the redshifted 21 cm brightness temperature and the duration of the reionization epoch. With refinement, this technique should be able to distinguish between slow and fast reionization scenarios. To constrain the duration of reionization to dz > 2, the systematic residuals in the measured spectrum must be reduced from 75 to 3 mK in future observations. This work was supported by the Massachusetts Institute of Technology, School of Science, and by the NSF through grant AST-0457585.

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