2010 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/152
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Item Quantitative measure of evolution of bright cluster galaxies at moderate redshifts(2010-01-01) Vikram, Vinu; et al.; Wadadekar, Yogesh; Kembhavi, A.K.Using archival data from the Hubble Space Telescope, we study the quantitative morphological evolution of spectroscopically confirmed bright galaxies in the core regions of nine clusters ranging in redshift from z = 0.31 to z = 0.84. We use morphological parameters derived from two dimensional bulge-disk decomposition to study the evolution. We find an increase in the mean bulge-to-total luminosity ratio B/T as the Universe evolves. We also find a corresponding increase in the fraction of early type galaxies and in the mean S´ersic index. We discuss these results and their implications to physical mechanisms for evolution of galaxy morphology.Item PyMorph: Automated galaxy structural parameter rstimation using python(2010-07-20) Vikram, Vinu; et al.; Wadadekar, Yogesh; Kembhavi, A.K.We present a new software pipeline – PyMorph – for automated estimation of structural parameters of galaxies. Both parametric fits through a two dimensional bulge disk decomposition as well as structural parameter measurements like concentration, asymmetry etc. are supported. The pipeline is designed to be easy to use yet flexible; individual software modules can be replaced with ease. A find-and-fit mode is available so that all galaxies in a image can be measured with a simple command. A parallel version of the Pymorph pipeline runs on computer clusters and a Virtual Observatory compatible web enabled interface is under development.Item Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152(2010-02-24) Srianand, R.; Gupta, Neeraj; Petitjean, Patrick; et al.We report the detection of 21-cm and molecular hydrogen absorption lines in the same damped Lyman-α system (with log N(H i)=21.36±0.10) at zabs=3.17447 towards SDSS J133724.69+315254.55 (zem ∼3.174). We estimate the spin temperature of the gas to be, TS = 600+222−159 K, intermediate between the expected values for cold and warm neutral media. This suggests that the H i absorption originates from a mixture of different phases. The total molecular fraction is low, fH2=10−7, and H2 rotational level populations are not in equilibrium. The average abundance of the α- elements is, [S/H]=−1.45 ± 0.22. Nitrogen and iron are found underabundant with respect to α-elements by ∼1.0 dex and ∼0.5 dex respectively. Using photoionization models we conclude that the gas, of mean density, nH ∼2 cm−3, is located more than 270 kpc away from the QSO. While the position of 21-cm absorption line coincides with the H2 velocity profile, its centroid is shifted by ∼2.7±1.0 km s−1 with respect to the redshift measured from the H2 lines. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km s−1. From this, we constrain the variation of the combination of fundamental constants x = α2Gp/µ, ∆x/x = −(1.7±1.7)×10−6. This system is unique as we can at the same time have an independent constrain on µ using H2 lines. However, as the H2 column density is low, only Werner band absorption lines are seen and, unfortunately, the range of sensitivity coefficients is too narrow to provide a stringent constraint: ∆µ/µ ≤ 4.0 × 10−4. The Ultraviolet and Visual Echelle Spectrograph (UVES) spectrum reveals another DLA at zabs= 3.16768 with log N(H i) = 20.41±0.15 and low metallicity, [Si/H] = −2.68 ± 0.11, in which [O/C] ∼ 0.18 ± 0.18 and [O/Si] ∼ 0. This shows that even in the very early stages of chemical evolution, the carbon or silicon to oxygen ratios can be close to solar. Using Voigt profile fitting we derive log(N(D i)/N(H i)) = −(4.93 ± 0.15) in this system. This is a factor of two smaller than the value expected from the best fitted value of Ωb from theWilkinson Microwave Anisotropy Probe (WMAP) 5 year data. This confirms the presence of astration of deuterium even at very low metallicity.Item Cosmic ray driven outflows from high redshift galaxies(2010-01-10) Samui, Saumyadip; Subramanian, Kandaswamy; Srianand, R.We study winds in high redshift galaxies driven by a relativistic cosmic ray (proton) component in addition to the hot thermal gas component. Cosmic rays (CRs) are likely to be efficiently generated in supernova(SNe)shocks inside galaxies. We obtain solutions of such CR driven free winds in a gravitational potential of the Navarro-Frenk-White (NFW) form, relevant to galaxies. Cosmic rays naturally provide the extra energy and/or momentum input to the system, needed for a transonic wind solution in a gas with adiabatic index = 5=3.We show that cosmic rays can effectively drive winds even when the thermal energy of the gas is lost due to radiative cooling. These wind solutions predict an asymptotic wind speed closely related to the circular velocity of the galaxy. Furthermore, the mass outflow rate per unit star formation rate ( w) is predicted to be ~ 0:2 0:5 for massive galaxies, with masses M ~ 1011 1012M .We show w to be inversely proportional to the square of the circular velocity. Magnetic fields at the G levels are also required in these galaxies to have a significant mass loss. A large w for small mass galaxies implies that cosmic ray driven outflows could provide a strong negative feedback to the star formation in dwarf galaxies. Further, our results will also have important implications to the metal enrichment of the intergalactic medium. These conclusions are applicable to the class of free wind models where the source region is confined to be within the sonic point.Item Bar fraction in lenticular galaxies: Dependence on luminosity and environment(2010-10-15) Barway, Sudhanshu; Wadadekar, Yogesh; Kembhavi, A.K.We present a study of bars in lenticular galaxies based on a sample of 371 galaxies from the SDSS-DR 7 and 2MASS in optical and near-infrared bands, respectively. We found a bar in 15% of the lenticular galaxies in our sample, which is consistent with recent stud- ies. The barred galaxy fraction shows a luminosity dependence, with faint lenticular galaxies (MK > −24.5, total absolute magnitude in K band) having a larger fraction of bars than bright lenticular galaxies (MK < −24.5). A similar trend is seen when Mr = −21.5, the total absolute magnitude in SDSS r band is used to divide the sample into faint and bright lenticular galaxies.We find that faint galaxies in clusters show a higher bar fraction than their counterparts in the field. This suggests that the formation of bars in lenticular galaxies not only depends on the total luminosity of galaxy but also on the environment of the host galaxy.Item Associated spectral and temporal state transition of the bright ULX NGC 1313 X-1(2010-05-21) Dewangan, Gulab Chand; et al.Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to different accretion disc geometries. We present analysis of two XMM-Newton observations of the Ultra-Luminous X-ray source (ULX) NGC 1313 X-1, which reveal that the system was in two different spectral states. While spectral variations have been observed in this source before, this data provides clear evidence that the spectral states also have distinct temporal properties. With a count rate of ~ 1.5 counts/s and a fractional variability amplitude of ~ 15%, the ULX was in a high flux and strongly variable state in March 2006. In October 2006, the count rate of the ULX had reduced by a factor of ~ 2 and the spectral shape was distinctly different with the presence of a soft component. No strong variability was detected during this low flux state with an upper limit on the amplitude < 3%. Moreover, the spectral properties of the two states implies that the accretion disc geometry was different for them. The low flux state is consistent with a model where a standard accretion disc is truncated at a ra- dius of ~ 17 Schwarzschild radius around a ~ 200M⊙ black hole. The inner hot region Comptonizes photons from the outer disc to give the primary spectral component. The spectrum of the high flux state is not compatible with such a geometry. Instead, it is consistent with a model where a hot corona covers a cold accretion disc and Comptonizes the disc photons. The variability as a function of energy is also shown to be consistent with the corona model. Despite these broad analogies with Galactic black hole systems, the spectral nature of the ULX is distinct in having a lower temperature (~ 2 keV) of the hot Comptonizing plasma and higher optical depth (~ 15) than what is observed for the Galactic ones.