Browsing by Author "Vivek, M."

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    Constraining fundamental constants of physics with quasar absorption line systems
    (2009-08-01) Petitjean, Patrick; Vivek, M.; Mohan, V.; et al.
    We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that fromthe Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [Oiii]λλ4960,5008 we put a 3σ limit on the relative acceleration to be less than 32 km s−1 yr −1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [Oiii]λ5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function.We infer the linear extent of this line emitting region is ∼ 8 kpc.We also find a tentative evidence for an offset between the centroid of the [Oiii]λ5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299◦ . This corresponds to the zem = 0.7128 system being at an impact parameter of ∼1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios
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    Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7
    (2009-08-01) Noterdaeme, P.; Vivek, M.; Mohan, V.
    We present the results of a search for damped Lyman-α (DLA) systems in the Sloan Digital Sky Survey II (SDSS), Data Release 7.We use a fully automatic procedure to identify DLAs and derive their column densities. The procedure is checked against the results of previous searches for DLAs in SDSS.We discuss the agreements and differences and show the robustness of our procedure. For each system, we obtain an accurate measurement of the absorber’s redshift, the Hi column density and the equivalent width of associated metal absorption lines, without any human intervention. We find 1426 absorbers with 2.15 < z < 5.2 with log N(Hi) ≥ 20, out of which 937 systems have log N(Hi) ≥ 20.3. This is the largest DLA sample ever built, made available to the scientific community through the electronic version of this paper. In the course of the survey, we discovered the intervening DLA with highest Hi column density known to date with log N(Hi) = 22.0 ± 0.1. This single system provides a strong constraint on the high-end of the N(Hi) frequency distribution now measured with high accuracy. We show that the presence of a DLA at the blue end of a QSO spectrum can lead to important systematic errors and propose a method to avoid them. This has important consequences for the measurement of the cosmological mass density of neutral gas at z ∼ 2.2 and therefore on our understanding of galaxy evolution over the past 10 billion years. We find a significant decrease of the cosmological mass density of neutral gas in DLAs, ΩDLA g , from z = 4 to z = 2.2, consistent with the result of previous SDSS studies. However, and contrary to other SDSS studies, we find that ΩDLA g (z = 2.2) is about twice the value at z = 0. This implies that ΩDLA g keeps decreasing at z < 2.2.
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    SDSS J092712.64+294344.0: recoiling black hole or merging galaxies
    (2009-08-01) Vivek, M.; Srianand, R.; Noterdaeme, P.; et al.
    We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that fromthe Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [Oiii]λλ4960,5008 we put a 3σ limit on the relative acceleration to be less than 32 km s−1 yr −1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [Oiii]λ5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function.We infer the linear extent of this line emitting region is ∼ 8 kpc.We also find a tentative evidence for an offset between the centroid of the [Oiii]λ5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299◦ . This corresponds to the zem = 0.7128 system being at an impact parameter of ∼1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and