Simulating the impact of HI fluctuations on matched filter search for ionized bubbles in redshifted 21 cm maps

May, 2008
12 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 391 (2008) 1900
e-Print:

Citations per year

20092013201720212024012345
Abstract: (arXiv)
Extending the formalism of Datta, Bharadwaj & Choudhury (2007) for detecting ionized bubbles in redshifted 21 cm maps using a matched-filtering technique, we use simulations to analyze the impact of HI fluctuations outside the bubble on the detectability of the bubble. In all the simulations there is a spherical bubble of comoving radius R_b, the one that we are trying to detect, located at the center, and the neutral hydrogen (HI) outside the bubble traces the underlying dark matter distribution. We consider three different possible scenarios of reionization, i.e., (i) there is asingle bubble (SB) in the field of view (FoV) and neutral fraction is constant outside this bubble (ii) patchy reionization with many small ionized bubbles in the FoV (PR1) and (iii) many spherical ionized bubbles of the same radius R_b (PR2). We make predictions for the currently functioning GMRT and a forthcoming instrument, the MWA at a redshift of 6 for 1000 hrs observations. We find that for both the SB and PR1 scenarios the fluctuating IGM restricts bubble detection to size R_b <=6 Mpc and R_b<=12 Mpc for the GMRT and the MWA respectively, however large be the integration time. These results are well explained by analytical predictions. In the PR2 scenario, we find that bubble detection is almost impossible for neutral fraction x_{HI}<0.6 because of large uncertainty due to the HI fluctuations. We find that determining the size and positions of the bubbles is not limited by the HI fluctuations in the SB and PR1 scenario but limited by the angular resolution of the array instead, and this can be done more precisely for larger bubble sizes. We also find that for detecting ionized bubbles the GMRT array configuration is somewhat superior to the proposed MWA.