Title:	HI fluctuations at large redshifts: I–visibility correlation
Authors:	Bharadwaj, Somnath Sethi, S.K.
Keywords:	Cosmology: theory, observations, Large scale structures—diffuseradiation.
Issue Date:	2001
Publisher:	Indian Academy of Sciences, Bangalore, India.
Citation:	Journal of Astrophysics and Astronomy, 2001, Vol. 22, p293-307
Abstract:	We investingate the possibility of probing the large scale structure in the universe at large redshifts by studying fluctuations in the redshifted 1420 MHz emission from the neutral hydrogen (HI) at early epochs. The neutral hydrogen content of the universe is known from absorption studies for z<˘4:5. The HI distribution is expected to be inhomogeneous in the gravitational instability picture and this inhomogeneity leads to an isotropy in the redshifted HI emission. The best hope of detecting this anisotropy is by using a large low-frequency interferometric instrument like the Giant Meter-Wave Radio Telescope (GMRT). We calculate the visibility correlation function hV .U/V 0.U/I at two frequencies v and nue of the redshifted HI emission for an interferometric observation. In particular we give numerical results for the two GMRT channels centered around v=325MHz and v=610MHz from density in homogeneity and peculiar velocity of the HI distribution. The visibility correlation is 10^−10–10^−9 Jy 2.We calculate the signal-to-noise for detecting the correlation signal in the presence of system noise and show that the GMRT might detect the signal for integration times =100hrs. We argue that the measurement of visibility correlation allows optimal use of the uncorrelated nature of the system noise across baselines and frequency channels.
URI:	http://hdl.handle.net/2289/761
ISSN:	0250-6335
Copyright:	Indian Academy of Sciences, Bangalore, India.
Appears in Collections:	Research Papers (A&A)

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