Non-local diffusion and the chemical structure of molecular clouds |
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| Authors: | J J Martinell D del-Castillo-Negrete A C Raga D A Williams |
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| Institution: | Department of Physics and Meteorology &Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India;Department of Mathematics, L.B.S. College, Gonda 271 001, India |
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| Abstract: | Observations of fluctuations in the redshifted 21-cm radiation from neutral hydrogen (H i ) are perceived to be an important future probe of the universe at high redshifts. Under the assumption that at redshifts z ≤ 6 (post-reionization era) the H i traces the underlying dark matter with a possible bias, we investigate the possibility of using observations of redshifted 21-cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expected signal is ～ 0.1 mJy at 325 MHz ( z = 3.4) for the small baselines at the Giant Metrewave Radio Telescope, the strength being a few times larger at higher frequencies (610 MHz, z = 1.3) . Further, the magnitude of the signal from the bispectrum is predicted to be comparable to that from the power spectrum, allowing a detection of both in roughly the same integration time. The H i signal is found to be uncorrelated beyond frequency separations of ～1.3 MHz whereas the continuum sources of contamination are expected to be correlated across much larger frequencies. This signature can in principle be used to distinguish the H i signal from the contamination. We also consider the possibility of using observations of the bispectrum to determine the linear and quadratic bias parameters of the H i at high redshifts, this having possible implications for theories of galaxy formation. |
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| Keywords: | intergalactic medium diffuse radiation large-scale structure of Universe |
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