IUCAA Preprints
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Item Effective radii and color gradients in radio galaxies(2015-03-11) Mahabal, A.; Kembhavi, A. K.; Mccarthy, P.J.We present de Vaucouleurs' effective radii in Band R bands for a sample of MRC radio galaxies and a control sample of normal galaxies. We use the ratio of the scale lengths in the two bands as an indicator to show that the radio galaxies tend to have excess of blue color in their inner region much more frequently than the control galaxies. We show that the scale length ratio is a useful indicator of radial color variation even when the conventional color gradient is too noisy to serve the purpose. We also discuss other interesting morphological features of radio galaxies including departures from de Vaucouleurs' law profiles in their central regions.Item Mega parsec relativistic jets launched from an accreting supermassive blackhole in an extreme spiral galaxy(IUCAA, 2015-02) Bagchi, Joydeep; Vivek, M.; Vikram, VinuItem 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 Radio observations of ZwCl 2341.1+0000: a double radio relic cluster(2009-10-01) Weeren, R.; Miniati, F.; Bagchi, Joydeep; et al.infall and mergers of smaller subclusters and galaxy groups. Diffuse radio emission, in the form of radio halos and relics, is found in clusters undergoing a merger, indicating that shocks or turbulence associated with the merger are capable of accelerating electrons to highly relativistic energies. Double relics are a rare class of radio sources found in the periphery of clusters, with the two components located symmetrically on the opposite sides of the cluster center. These relics are important probes of the cluster periphery as (i) they provide an estimate of the magnetic field strength, and (ii) together with detailed modeling can be used to derive information about the merger geometry, mass, and timescale. Observations of these double relics can thus be used to test the framework of LSS formation. Here we report on radio observations of ZwCl 2341.1+0000, a complex merging structure of galaxies located at z = 0.27, using Giant Metrewave Radio Telescope (GMRT) observations. Aims. The main aim of the observations is to study the nature of the diffuse radio emission in the galaxy cluster ZwCl 2341.1+0000. Methods. We carried out GMRT 610, 241, and 157 MHz continuum observations of ZwCl 2341.1+0000. The radio observations are combined with X-ray and optical data of the cluster. Results. The GMRT observations show a double peripheral radio relic in the cluster ZwCl 2341.1+0000. The spectral index is −0.49 ± 0.18 for the northern relic and −0.76 ± 0.17 for the southern relic. We have derived values of 0.48 − 0.93 µGauss for the equipartition magnetic field strength. The relics are probably associated with outward traveling merger shock waves.Item X-Ray warm absorption and emission in the polar scattered seyfert 1 galaxy MRK 704(2011-04-10) Laha, Sibasish; Dewangan, Gulab Chand; Kembhavi, A.K.