2006 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/335
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Item Velocity-metallicity correlation for high-z DLA galaxies: Evidence for a mass-metallicity relation?(2006-06-08) Ledoux, C.; Petitjean, Patrick; Fynbo, J. P. U.; et al.Item Multiwavelength investigation of a near-solar metallicity sub-DLA at Zabs=1.3647 towards PKS 0237-233(2006-11-10) Srianand, R.; Gupta, Neeraj; Petitjean, PatrickItem Metallicity as a criterion to select H2 bearing damped lyman-alpha systems(2006-07-17) Petitjean, Patrick; Ledoux, C.; Noterdaeme, P.; et al.Item Detecting cold gas at intermediate redshifts: GMRT survey using MgII systems(2006-11-28) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.Intervening H i 21-cm absorption systems at z ≥ 1.0 are very rare and only 4 confirmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the interstellar medium of high-z galaxies. Moreover, they can provide independent constraints on the variation of fundamental constants. We report 3 new detections based on our ongoing Giant Metrewave Radio Telescope (GMRT) survey for 21-cm absorbers at 1.10 ≤ zabs ≤ 1.45 from candidate damped Lyman-α systems. The 21-cm lines are narrow for the zabs= 1.3710 system towards SDSS J0108−0037 and zabs= 1.1726 system toward SDSS J2358−1020. Based on line full-width at half maximum, the kinetic temperatures are ≤ 5200 K and ≤ 800 K, respectively. The 21-cm absorption profile of the third system, zabs=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex, extending up to 100 km s−ᶥ . The centroids of the 21-cm lines are found to be shifted with respect to the corresponding centroids of the metal lines derived from SDSS spectra. This may mean that the 21-cm absorption is not associated with the strongest metal line component.Item Bulk motion of ultrarelativistic conical blazar jets(2006-03-27) Krishna, Gopal; Wiita, Paul J.; Dhurde, SamirAllowing for the conical shape of ultrarelativistic blazar jets with opening angles of a few degrees on parsec-scales we show that their bulk Lorentz factors and viewing angles can be much larger than the values usually inferred by combining their flux variability and proper motion measurements. This is in accord with our earlier finding that such ultrarelativistic (Lorentz factor, Γ > 30) conical jets can reconcile the relatively slow apparent motions of VLBI knots in TeV blazars with the extremely fast flows implied by their rapid γ-ray variability. This jet geometry also implies that deprojected jet opening angles will typically be significantly underestimated from VLBI measurements. In addition, de-projected jet lengths will be considerably overestimated if high Lorentz factors and significant opening angles are not taken into account.