Simulated Predictions For H I At Z=3.35 With The Ooty Wide Field Array (Owfa) - Ii. Foreground Avoidance

Considering the upcoming OWFA, we use simulations of the foregrounds and the z = 3.35 H I 21-cm intensity mapping signal to identify the (k(perpendicular to), k(parallel to)) modes where the expected 21-cm power spectrum P(k(perpendicular to), k(parallel to)) is substantially larger than the predicted foreground contribution. Only these uncontaminated k modes are used for measuringP(k(perpendicular to), k(parallel to)) in the "Foreground Avoidance" technique. Though the foregrounds are largely localized within a wedge. we find that the small leakage beyond the wedge surpasses the 21-cm signal across a significant part of the (k(perpendicular to), k(parallel to)) plane. The extent of foreground leakage is extremely sensitive to the frequency window function used to estimate P(k(perpendicular to), k(parallel to)). It is possible to reduce the leakage by making the window function narrower; however, this comes at the expense of losing a larger fraction of the 21-cm signal. It is necessary to balance these competing effects to identify an optimal window function. Considering a broad class of cosine window functions, we identify a six term window function as optimal for 21-cm power spectrum estimation with OWFA. Considering only the k modes where the expected 21-cm power spectrum exceeds the predicted foregrounds by a factor of 100 or larger, a 5 sigma detection of the binned power spectrum is possible in the k-ranges 0.18 <= k <= 0.3 Mpc(-1) and 0.18 <= k <= 0.8 Mpc(-1) with 1000-2000 and 10(4) h of observation, respectively.