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 Re-analysis of the three-year wilkinson microwave anisotropy probe temperature power spectrum and likelihood(2006-10-02) Eriksen, H. K.; Huey, Greg; Saha, Rajib; et al.We analyze the three-year WMAP temperature anisotropy data seeking to confirm the power spectrum and likelihoods published by the WMAP team. We apply five independent implementations of four algorithms to the power spectrum estimation and two implementations to the parameter estimation. Our single most important result is that we broadly confirm the WMAP power spectrum and analysis. Still, we do find two small but potentially important discrepancies: On large angular scales there is a small power excess in the WMAP spectrum (5–10% at ℓ . 30) primarily due to likelihood approximation issues between 13 ≤ ℓ . 30. On small angular scales there is a systematic difference between the V- and W-band spectra (few percent at ℓ & 300). Recently, the latter discrepancy was explained by Huffenberger et al. (2006) in terms of over-subtraction of unresolved point sources. As far as the low-ℓ bias is concerned, most parameters are affected by a few tenths of a sigma. The most important effect is seen in ns. For the combination of WMAP, Acbar and BOOMERanG, the significance of ns = 1 drops from ∼ 2.7σ to ∼ 2.3σ when correcting for this bias. We propose a few simple improvements to the low-ℓ WMAP likelihood code, and introduce two important extensions to the Gibbs sampling method that allows for proper sampling of the low signal-to-noise regime. Finally, we make the products from the Gibbs sampling analysis publically available, thereby providing a fast and simple route to the exact likelihood without the need of expensive matrix inversions.Item Non-circular beam correction to the CMB power spectrum(2006-08-24) Souradeep, Tarun; Mitra, Sanjit; Sengupta, Anand; et al.In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo-Cl method, are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. When non-circular beam effect is important, we advocate that it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transform die down fast with m.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.