Browsing by Author "Nath, B. B."
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Item Neutral hydrogen at high redshifts as a probe of structure formation – III. Radio maps from N-body simulations.(Wiley-Blackwell, 1997-04-04) Bagla, J. S.; Nath, B. B.; Padmanabhan, T.Large inhomogeneities in neutral hydrogen in the universe can be detected at redshifts z 10 using the redshifted 21cm line emission. We use cosmological N-Body simulations for dark matter and a simple model for baryonic collapse to estimate the signal expected from structures like proto-clusters of galaxies at high redshifts.We study : (i) the standard CDM model, (ii) a modified CDM model with less power at small scales, and (iii) a +CDM model in a universe with 0 + = 1. We show that it should be possible for the next generation radio telescopes to detect such structures at the redshift 3.34 with an integration of about 100 hours. We also discuss possible schemes for enhancing signal to noise ratio to detect proto-condensates at high redshifts.Item On the interpretation of the He II absorption in the line of sight of Q0302-003(2015-01-27) Nath, B. B.; Sethi, Shiv K.We point out the peculiarities of the line of sight of Q0302-003 which was recently used to estimate the He II opacity at z∼3.285. This line of sight contains a large void in Lyman α clouds, in the region used for the He II opacity observation, and the void is thought to be caused by the ionizing radiation from a foreground quasar (Dobrzycki and Bechtold 1991). If this is true, then the radiation from the foreground quasar is more relevant in the region used for the estimation of the He II opacity than the diffuse UV background radiation. We argue that in that case the observed opacity should not be used to put constraint on the diffuse UV background radiation. Using a typical spectral index of quasars, we estimate that most of the observed He II opacity must be due to Gunn-Peterson effect and suggest a H I Gunn-Peterson test along this line of sight. We further discuss the clumpiness of the intergalactic medium in the vicinity of Q0302-003 as suggested by observationsItem Primordial magnetic fields and formation of molecular hydrogen(2009-04-01) Sethi, Shiv K.; Nath, B. B.; Subramanian, Kandaswamy; et al.We study the implications of primordial magnetic fields for the thermal and ionization history of the post-recombination era. In particular we compute the effects of dissi- pation of primordial magnetic fields owing to ambipolar diffusion and decaying tur- bulence in the intergalactic medium (IGM) and the collapsing halos and compute the effects of the altered thermal and ionization history on the formation of molecular hy- drogen.We show that, for magnetic field strengths in the range 2×10−10 G < ∼ B0 < ∼ 2× 10−9 G, the molecular hydrogen fraction in IGM and collapsing halo can increase by a factor 5 to 1000 over the case with no magnetic fields. We discuss the implication of the increased molecular hydrogen fraction on the radiative transfer of UV photons and the formation of first structures in the universeItem Vanishing sunspots(Hindu Group of Publication, 2010-12-04) Nath, B. B.A solar storm brings hope to scientists who were worried about the lack of sunspots and the consequences of this for the earth.