Research Publications
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Item Statistical significance of a large quasar inhomogeneity in the sky(EDP Sciences, 1985-05-09) Narlikar, J. V.; Subramanian, KandaswamyStatistical techniques are devised to study the significance of apparent inhomogeneities in the distribution of points on a spherical surface, especially in the form of jets and chains. The methods are applied to complete samples of radio quasars in specific windows of magnitudes and redshifts. It is found that while most of the distributions studied show very little evidence of non-randomness, the inhomogeneity reported by Arp (1984) is highly significant. There is also some evidence, although a statistically weaker one, for a chainlike structure in the distribution of low redshift quasars in another area of the sky.Item Single exhaust model for backward emission in fast moving quasars(Liege University Press, Liege, 1983-01-01) Subramanian, Kandaswamy; Narlikar, J. V.Item Quasars Q 2345 + 007 A,B and 3C 273 : Gravitational Lenses?(Liege University Press, Liege, 1983-01-14) Narlikar, J. V.; Subramanian, Kandaswamy; Narasimha, D.; et al.Item Single exhaust model for backward emission in doppler quasars(American Astronomical Society, 1983-10-01) Narlikar, J. V.; Subramanian, KandaswamyThis paper provides an astrophysical scenario for Hoyle's (1980) conjecture that quasars ejected at high velocities from active galactic nuclei predominantly radiate in a narrow backward cone. Through such backward emission, local Doppler theory can explain the fact that no blueshifted quasars are seen. It is held that a fast moving quasar encounters a strong ram pressure from the intergalactic medium in the forward direction which suppresses the forward exhaust. Attention is given to the hydrodynamic, gravitation theory, and radiation requirement constraints on the model, which is shown to accommodate them over a comfortable range of parameters, and which also helps in the understanding of some of the observable properties of quasars.Item Observational limitations of the Doppler theory of quasars(American Astronomical Society, 1982-09-13) Narlikar, J. V.; Subramanian, KandaswamyItem Zeldovich approximation and the probability distribution for the smoothed density field in the nonlinear regime(American Astronomical Society, 1993-06-20) Padmanabhan, T.; Subramanian, KandaswamyThe study of large-scale structure in the Universe is often based on the observed density distribution of matter smoothed by a suitable filter function. The probability distribution for this smoothed density field in the nonlinear regime is studied using the Zel'dovich approximation. When the shear term of the velocity field is not too large, one can obtain a reasonably good analytic approximation tho this probability distribution. The properties of this distribution are discussed and compared with other attempts along similar lines.Item Galaxy Formation(Astronomical Society of India, 1992-10-15) Padmanabhan, T.; Subramanian, KandaswamyItem Focusing equations, caustics and the condition for multiple imaging by thick gravitational lenses(Royal Astronomical Society, 1987-12-27) Padmanabhan, T.; Subramanian, KandaswamyThe condition for the production of multiple images by an arbitrary (thick or thin) gravitational lens are studied. We show that the necessary and sufficient condition for the production of multiple images by a lens is the following: The lens should produce a point conjugate to the observer, along some null geodesic, at an affine distance smaller than that of the source. It is shown that previous results on multiple imaging by thin lenses can be obtained as a special case. We also show that a thick lens cannot be more efficient than a suitably designed thin lens for the production of multiple images.Item Aspects of Zeldovich approximation(American Astronomical Society, 1993-04-15) Padmanabhan, T.; Subramanian, KandaswamyA generalized version of the Zel'dovich approximation which is applicable in both the radiation-dominated and the matter dominated epochs is presented. This approximation allows one to follow the growth of inhomogeneities from the time the mode enters the hubble radius until it turns around. Comparison of the results with the standard spherical model shows that the analytical approximation is quite good even in the nonlinear regime. Detailed application to cold dark matter models and seeded models are given.Item Neutral hydrogen at high redshifts as a probe of structure formation- II. Line profile of a protocluster(Wiley-Blackwell, 1994-09-05) Kumar, A.; Padmanabhan, T.; Subramanian, KandaswamyThe formation of structures at z ≤ 10.0 can be probed using the 21-cm line emisssion from the neutral hydrogen. Two of us (KS and TP, Paper I) previously computed the expected abundance of protoclusters as a function of the flux density at various redshifts, in the cold dark matter (CDM) and the hot dark matter (HDM) models. As a complement to Paper I, here we work out in detail how the H1 line profile from a spherically symmetric protocluster evolves as it decouples from Hubble expansion structures form hierarchically. Neutral hydrogen, in the small-scale clumps that from the protocluster, is the source of H1line profile in this model are typically of order 0.5-0.7 mJy, while the widths (FWHM) are of order 0.3-1.8 MHz. The major uncertainty in our calculations is the fraction of mass of the protocluster in the form of neutral hydrogen. If the neutral hydrogen fraction f is of the order of the value we have adopted (f=0.025) in our calculations or greater, then a typical protocluster could indeed be detectable by future facilities, like the Giant Metrewave Radio Telescope (GMRT) which is currently being built in India. If the neutral hydrogen fraction is much less than the value we have adopted, then a more sensitive instrument is needed to detect the H1 line emission from a typical protocluster.