IUCAA Preprints
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Item Outflowing material in the CSS quasar 3C48: evidence of jet-cloud interaction?(2005-05-01) Gupta, Neeraj; Srianand, R.; Saikia, D. J.We report the detection of a zabs=0.3654 associated absorption-line system in the UV spectrum of the CSS quasar 3C48. The absorbing material is blue shifted with respect to the quasar emission-line redshift, zem =0.3700, suggesting an outflow velocity of ∼1000 km s−1. We detect absorption lines over a range of ionization states from Lyβ, Lyγ, C iv, N iv, S vi to O vi and possibly O iv and Ne viii. The kinematical properties of the absorption-line system are similar to the blue-shifted emission line gas seen in [Oiii] λ5007 (Chatzichristou, Vanderriest & Jaffe 1999), which is believed to have interacted with the radio jet. We study the properties of the absorbing material using CLOUDY and find that photoionization models with Solar abundance ratios (with overall metallicity in the range 0.16Z/Z⊙61.3) are enough to explain the observed column densities of all the species except Ne viii , detection of which requires confirmation. Since the cooling and recombination time for the gas is ∼105 yr, the consistency with the photoionization models suggests that any possible interaction of absorbing material with the jet must have taken place before ∼105 yr. The abundance ratio of nitrogen to carbon is close to Solar values, unlike in the case of most quasars, especially at high-redshifts, which have super-Solar values.We observed 3C48 with the Giant Metrewave Radio Telescope (GMRT) to search for redshifted 21cm H i absorption. However, we did not detect any significant feature in our spectra and estimate the 3σ upper limit to the optical depth to be in the range 0.001 to 0.003. However, due to the diffuse nature of the radio source, optical depths as high as 0.1 towards individual knots or compact components cannot be ruled out.Item Kinematical diagrams for conical relativistic jets(2007-03-10) Gopal, Krishna; Sircar, Pronoy; Dhurde, SamirWe present diagrams depicting the expected inter-dependences of two key kinematical parameters of radio knots in the parsec-scale jets of blazars, deduced from VLBI observations. The two parameters are the apparent speed (vapp = cfJapp) and the effective Doppler boosting factor (Oeff) of the relativistically moving radio knot. A novel aspect of these analytical computations of fJ-o diagrams is that they are made for parsecscale jets having a conical shape, with modest opening angles (w up to 10°), in accord with the VLBI observations of the nuclei of the nearest radio galaxies. Another motivating factor is the recent finding that consideration of a conical geometry can have important implications for the interpretation of a variety of radio observations of blazar jets. In addition to uniform jet flows (i.e., those having a uniform bulk Lorentz factor, r), computational results are also presented for stratified jets where an ultra-relativistic central spine along the jet axis is surrounded by a slower moving sheath, possibly arising from a velocity shear.