Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-11-28
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
16 pages, 13 figures, 2 tables. Major changes in the results from the previous version. Submitted in MNRAS. Replaced to match
Scientific paper
The infrared detection of a z>7 quasar has opened up a new window to directly probe the IGM during the epoch of reionization. In this paper we theoretically consider the possibility of detecting the ionized bubble around a z=8 quasar using targeted redshifted 21-cm observations with the GMRT. The apparent shape and size of the ionized bubble, as seen by a distant observer, depends on the parameters \dot{N}_{phs}/C, x_HI/C and \tau_Q where \dot{N}_{phs}, \tau_Q x_HI and C are respectively the ionizing photon emission rate, age of the quasar, the neutral fraction and clumping factor of the IGM. In the current work we have analytically calculated the apparent shape and size of a quasar's ionized bubble assuming an uniform IGM and ignoring other ionizing sources besides the quasar, and used this as a template for matched filter bubble search with the GMRT visibility data. We have assumed that \dot{N}_{phs} is known from the observed infrared spectrum and C from theoretical considerations, which gives us the two free parameters x_HI and \tau_Q for bubble detection. Considering 1,000 hr of observation, we find that there is a reasonably large region of parameter space where a 3\sigma detection is possible. We also find that it will be possible to place lower limits on x_HI and \tau_Q with 1,000 hr of observation. Deeper follow up bservations can place upper limits on \tau_Q and x_HI. We have used the semi-numerical technique to simulate the apparent shape and size of quasar ionized bubbles considering the presence of other ionizing sources and inhomogeneities in the IGM. We find that the presence of other sources increase the size of the quasar bubble, leading to x_HI being underestimated. Clustering of other ionizing sources around the quasar can produce severe distortions in bubble's shape. However, this does not severely affect parameter estimation in the bubbles that are large.
Bharadwaj Somnath
Choudhury Tirthankar Roy
Majumdar Suman
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