Constrainingquasar and intergalactic medium properties through bubble detection in redshifted 21cm maps
Abstract
The infrared detection of a z > 7 quasar has opened up a window to directly probe the intergalactic medium (IGM) during the epoch of reionization. It is anticipated that future observations will yield more quasars extending to higher redshifts. In this paper, we theoretically consider the possibility of detecting the ionized bubble around a z = 8 quasar using targeted redshifted 21cm observations with the GMRT. The apparent shape and size of the ionized bubble, as seen by a distant observer, depends on the parameters N˙ phs /C, xH i /c and τ_{Q}, where N˙ phs and τ_{Q} are, respectively, the ionizing photon emission rate and age of the quasar, and xH i and C are, respectively, the neutral fraction and clumping factor of the IGM. The 21cm detection of an ionized bubble, thus, holds the promise of allowing us to probe the quasar and IGM properties at z = 8.
In this work we have analytically calculated the apparent shape and size of a quasar's ionized bubble assuming a uniform IGM and ignoring other ionizing sources besides the quasar, and used this as a template for matchedfilter bubble search with the GMRT visibility data. We have assumed that N˙ phs is known from the observed infrared spectrum, and C = 30 from theoretical considerations, which gives us the two free parameters xH i and τ_{Q} for bubble detection. Considering 1000'h of observation, we find that there is a reasonably large region of parameter space bounded within (xH i , (τQ/107 yr ))=(1.0, 0.5) and (0.2, 7.0) where a 3σ detection is possible if (N˙ phs /1057 s1)=3. The available region increases if N˙ phs is larger, whereas we need xH i ≥0.4 and (τQ/107 yr )≥2.0 if (N˙ phs /1057 s1)=1.3. Considering parameter estimation, we find that in many cases it will be possible to quite accurately constrain τ_{Q} and place a lower limit on xH i with 1000'h of observation, particularly if the bubble is in the early stage of growth and we have a very luminous quasar or a high neutral fraction. Deeper followup observations (4000 and 9000'h) can be used to further tighten the constraints on τ_{Q} and xH i . We find that the estimated xH i is affected by uncertainty in the assumed value of C. The quasar's age τ_{Q} however is robust and is unaffected by the uncertainty in C.
The presence of other ionizing sources and inhomogeneities in the IGM distort the shape and size of the quasar's ionized bubble. This is a potential impediment for bubble detection and parameter estimation. We have used the seminumerical technique to simulate the apparent shape and size of quasar ionized bubbles incorporating these effects. If we consider a 9000'h of observation with the GMRT, we find that the estimated parameters τ_{Q} and xH i are expected to be within the statistical uncertainties.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2012
 DOI:
 10.1111/j.13652966.2012.21914.x
 arXiv:
 arXiv:1111.6354
 Bibcode:
 2012MNRAS.426.3178M
 Keywords:

 methods: data analysis;
 cosmology: theory;
 diffuse radiation;
 Astrophysics  Cosmology and Extragalactic Astrophysics
 EPrint:
 18 pages, 16 figures, 3 tables. Minor change in text. Accepted for publication in MNRAS