2005 (IPP)
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Item VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas(2005-06-01) Srianand, R.; Petitjean, Patrick; Ledoux, C´edric; et al.We study the physical conditions in damped Lyman-α systems (DLAs), using a sample of 33 systems toward 26 QSOs acquired for a recently completed survey of H2 by Ledoux et al. (2003). We use the column densities of H2 in different rotational levels, together with those of C i, C i ∗, C i ∗∗, C ii ∗ and singly ionized atomic species to discuss the kinetic temperature, the density of hydrogen and the electronic density in the gas together with the ambient UV radiation field. Detailed comparisons are made between the observed properties in DLAs, the interstellar medium (ISM) of the Galaxy, the large and small Magellanic clouds (LMC and SMC).The mean kinetic temperature of the gas corresponding to DLA subcomponents in which H2 absorption line is detected, derived from the ortho-to-para ratio (153±78 K), is higher than that measured in the ISM (77±17 K) and the Magellanic clouds (82±21 K). Typical pressure in these components (corresponding to T = 100−300 K and nH = 10−200 cm−3), measured using C i fine-structure excitation, are higher than what is measured along ISM sightlines. This is consistent with the corresponding higher values for N(H2,J=2)/N(H2,J=0) seen in DLAs. From the column densities of the high-J rotational levels, we derive that the typical radiation field in the H2 bearing components is of the order of or slightly higher than the mean UV field in the Galactic ISM. Determination of electron density in the gas with H2 and C i show the ionization rate is similar to that of a cold neutral medium (CNM) in a moderate radiation field. This, together with the fact that we see H2 in 13-20% of the DLAs, can be used to conclude that DLAs at z > 1.9 could contribute as much as 50% star formation rate density seen in Lyman break galaxies (LBGs).C ii ∗ absorption line is detected in all the components where H2 absorption line is seen. The excitation of C ii in these systems is consistent with the physical parameters derived from the excitation of H2 and C i. We detect C ii ∗ in about 50% of the DLAs and therefore in a considerable fraction of DLAs that do not show H2. In part of the later systems, physical conditions could be similar to that in the CNM gas of the Galaxy. However, the absence of C i absorption line and the presence of Al iii absorption lines with a profile similar to the profiles of singly ionized species suggest an appreciable contribution from warm (WNM) and/or partially ionized gas. The absence of H2, for the level of metallicity and dust depletion seen in these systems, are consistent with low densities (i.e nH 6 1 cm−3) for a radiation field similar to the mean Galactic UV field.Item Understanding Our Universe : Current Status and Open Issues(2005-03-01) Padmanabhan, T.Last couple of decades have been the golden age for cosmology. High quality data confirmed the broad paradigm of standard cosmology but have thrusted upon us a preposterous composition for the universe which defies any simple explanation, thereby posing probably the greatest challenge theoretical physics has ever faced. Several aspects of these developments are critically reviewed, concentrating on conceptual issues and open questions.Item Plane symmetric inhomogeneous bulk viscous domain wall in Lyra geometry(2005-07-01) Pradhan, Anirudh; Rai, Vandana; Otarod, SaeedSome bulk viscous general solutions are found for domain walls in Lyra geometry in the plane symmetric inhomogeneous spacetime. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field β. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. Some physical consequences of the models are also given. Finally, the geodesic equations and acceleration of the test particle are discussed.Item New constraint on the time dependence of the proton-to-electron mass ratio. Analysis of the Q 0347-383 and Q 0405-443 spectra(2005-07-01) Ivanchik, A.; Srianand, R.; Varshalovich, D.A new limit on the possible cosmological variation of the proton-to-electron mass ratio µ = mp/me is estimated by measuring wavelengths of H2 lines of Lyman and Werner bands from two absorption systems at zabs = 2.5947 and 3.0249 in the spectra of quasars Q 0405−443 and Q 0347−383, respectively. Data are of the highest spectral resolution (R = 53000) and S/N ratio (30÷70) for this kind of study. We search for any correlation between zi, the redshift of observed lines, determined using laboratory wavelengths as references, and Ki, the sensitivity coefficient of the lines to a change of µ, that could be interpreted as a variation of µ over the corresponding cosmological time. We use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et al. 1993), based on experimental determination of energy levels and the second one, Set (P) (Philip et al. 2004), based on new laboratory measurements of some individual rest-wavelengths. We find ∆µ/µ = (3.05±0.75)×10−5 for Set (A), and ∆µ/µ = (1.65±0.74)×10−5 for Set (P). The second determination is the most stringent limit on the variation of µ over the last 12 Gyrs ever obtained. The correlation found using Set (A) seems to show that some amount of systematic error is hidden in the determination of energy levels of the H2 molecule.Item Kinematics and star formation activity in the z=2.03954 damped Lyman-alpha system towards PKS 0458-020(2005-12-01) Heinmuller, Janine; Srianand, R.; Petitjean, Patrick; et al.We present UVES observations of the log N(H ) = 21.7 damped Lyman-α system at zabs = 2.03954 towards the quasar PKS 0458−020. H Lyman-α emission is detected in the center of the damped Lyman-α absorption trough. Metallicities are derived for Mg , Si , P , Cr , Mn , Fe and Zn and are found to be −1.21 ± 0.12, −1.28 ± 0.20, −1.54 ± 0.11, −1.66 ± 0.10, −2.05 ± 0.11, −1.87 ± 0.11, −1.22 ± 0.10, respectively, relative to solar. The depletion factor is therefore of the order of [Zn/Fe] = 0.65. We observe metal absorption lines to be blueshifted compared to the Lyman-α emission up to a maximum of ∼100 and 200 km s−1 for low and high-ionization species respectively. This can be interpreted either as the consequence of rotation in a large (∼7 kpc) disk or as the imprint of a galactic wind. The star formation rate (SFR) derived from the Lyman-α emission, 1.6M⊙yr −1 , is compared with that estimated from the observed C ∗ absorption. No molecular hydrogen is detected in our data, yielding a molecular fraction log f < −6.52. This absence of H2 can be explained as the consequence of a high ambient UV flux which is one order of magnitude larger than the radiation field in the ISM of our Galaxy and originates in the observed emitting region.Item Kaluza-Klein Type Robertson Walker Cosmological Model With Dynamical Cosmological Term Lambda(2005-12-01) Pradhan, Anirudh; Khadekar, G. S.; Patki, VrishaliIn this paper we have analyzed the Kaluza-Klein type RobertsonWalker (RW) cosmological models by considering three different forms of variable Λ: Λ ∼˙ a a 2 , Λ ∼ ¨ a a and Λ ∼ ρ. It is found that, the connecting free parameters of the models with cosmic matter and vacuum energy density parameters are equivalent, in the context of higher dimensional space time. The expression for the look back time, luminosity distance and angular diameter distance are also derived. This work has thus generalized to higher dimensions the well-known results in four dimensional space time. It is found that there may be significant difference in principle at least, from the analogous situation in four dimensional space time.Item Dark energy and cosmological solutions in second-order string gravity(2005-09-01) Calcagni, Gianluca; Tsujikawa, Shinji; Sami, M.We study the cosmological evolution based upon a D-dimensional action in low-energy effective string theory in the presence of second-order curvature corrections and a modulus scalar field (dilaton or compactification modulus). Abarotropic perfect fluid coupled to the scalar field is also allowed. Phase space analysis and the stability of asymptotic solutions are performed for a number of models which include (i) fixed scalar field, (ii) linear dilaton in string frame, and (iii) logarithmic modulus in Einstein frame. We confront analytical solutions with observational constraints for deceleration parameter and show that Gauss-Bonnet gravity (with no matter fields) may not explain the current acceleration of the universe. We also study the future evolution of the universe using the GB parametrization and find that big rip singularities can be avoided even in the presence of a phantom fluid because of the balance between the fluid and curvature corrections. A non-minimal coupling between the fluid and the modulus field also opens up the interesting possibility to avoid big rip regardless of the details of the fluid equation of state.Item Cosmological cosmic rays and the observed Li6 plateau in metal poor halo stars(2005-01-01) Rollinde, Emmanuel; Elisabeth, Vangioni-Flam; Olive, Keith AVery recent observations of the 6Li isotope in halo stars reveal a 6Li plateau about 1000 times above the predicted BBN abundance. We calculate the evolution of 6Li versus redshift generated from an initial burst of cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that the pregalactic production of the 6Li isotope can account for the 6Li plateau observed in metal poor halo stars without additional overproduction of 7Li. The derived relation between the amplitude of the CCR energy spectra and the redshift of the initial CCR production puts constraints on the physics and history of the objects, such as pop III stars, responsible for these early cosmic rays. Consequently, we consider the evolution of 6Li in the Galaxy. Since 6Li is also produced in Galactic cosmic ray nucleosynthesis, we argue that halo stars with metalIicities between [Fe/H) = -2 and -1, must be somewhat depleted in 6Li.