2007 (IPP)
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Item Virtual observatories and developing countries(2007-01-04) Kembhavi, A.K.I will discuss in this artical the emerging concept of Virtual Observatories, the efforts being made in various countries to set up these structures, and the relevance of the concept to astronomy in developing countries.Item Unravelling the morphologies of Luminous Compact Galaxies using the HST/ACS GOODS survey(2007-04-17) Rawat, A.; Kembhavi, A.K.; Barway, Sudhanshu; et al.Context. Luminous Compact Galaxies (LCGs) (MB ≤ −20, R1/2 ≤ 4.5 kpc and EW0(OII) ≥15Å) constitute one of the most rapidly evolving galaxy populations over the last ∼8Gyr history of the universe. Due to their inherently compact sizes, any detailed quantitative analysis of their morphologies has proved to be difficult in the past. Hence, the morphologies and thereby the local counterparts of these enigmatic sources have been hotly debated. Aims. Our aim is to use the high angular resolution, deep, multiband HST/ACS imaging data, from the HST/ACS GOODS survey, to study the quantitative morphology of a complete sample of LCGs in the redshift range 0.5 ≤ z ≤ 1.2. Methods. We have derived structural parameters for a representative sample of 39 LCGs selected from the GOODS-S HST/ACS field, using full 2-dimensional surface brightness profile fitting of the galaxy images in each of the four filters available. B435W − z850LP color maps are constructed for the sample to aid in the morphological classification. We then use the rest frame B band bulge flux fraction (B/T) to determine the morphological class of galaxies which are well fit by a ulge+disk two dimensional structure. Mergers were essentially identified visually by the presence of multiple maxima of comparable intensity in the rest frame B band images, aided by the color maps to distinguish them from HII regions. We also make use of the Spitzer 24 m source catalog of sources in the CDFS to derive the dust enshrouded star formation rates (SFR) for some of the sample LCGs Results. We derive the following morphological mix for our sample of intermediate redshift LCGs: Mergers: ∼36%, Disk dominated: ∼22%, S0: ∼20%, Early types: ∼7%, Irr/tadpole: ∼15%.We establish that our sample LCGs are intermediate mass objects with stellar mass ranging from 9.44 ≤ Log10(M/M⊙) ≤ 10.96, with a median mass of Log10(M/M⊙) = 10.32. We also derive SFR values ranging from a few to ∼ 65 M⊙/year as expected for this class of objects. We find that LCGs account for ∼26% of the MB ≤ −20 galaxy population in the redshift range 0.5 ≤ z ≤ 1.2. We estimate a factor ∼11 fall in the comoving number density of blue LCGs from redshifts 0.5 ≤ z ≤ 1.2 to the current epoch, even though this number is subject to large uncertainities given the small sample size at zero redshift available from the literature. Conclusions. The strong redshift evolution exhibited by LCGs, and the fact that a significant fraction of LCGs are in merging systems, seem to indicate that LCGs might be an important phase in the hierarchical evolution of galaxies. We envisage that some of the LCGs that are classified as merging systems, might go on to rebuild their disks and evolve into disk galaxies in the local universe.Item Type I singularities and the Phantom Menace(2007-04-15) Naskar, Tapan; Ward, JohnWe consider the future dynamics of a transient phantom dominated phase of the universe in LQC and in the RS braneworld, which both have a non-standard Friedmann equation. We find that for a certain class of potentials, the Hubble parameter oscillates with simple harmonic motion in the LQC case and therefore avoids any future singularity. For more general potentials we find that damping effects eventually lead to the Hubble parameter becoming constant. On the other hand in the braneworld case we find that although the type I singularity can be avoided, the scale factor still diverges at late times.Item Theoretical spectra of PAHs in modeling astrophysical IR features(2007-11-18) Pathak, Amit; Rastogi, ShantanuItem Theoretical infrared spectra of large polycyclic aromatic hydrocarbons(2007-11-18) Pathak, Amit; Rastogi, ShantanuTheoretical and experimental spectroscopic studies have underlined the contribution of large PAHs towards the astrophysical mid-infrared emission bands. Quantum chemical study of eight large PAHs using density functional theory approach is reported along with their infrared spectra. Systematic variation of bands with PAH size is noted and a better agreement with the observed astrophysical bands is obtained. Compared to small and medium sized PAHs there is substantial C ¡ H stretch intensity in the cation spectra. This is attributed to smaller change in charge on the hydrogens upon ionization. For the C ¡ H out-of-plane mode large PAHs correlate well with observed features on the shorter wavelength side of the 11.2 ¹m band. Presence of two sub-components of the broad 7.7 ¹m band in large PAHs compares very well with the corresponding astrophysical band and point to the abundance of large PAH cations in interstellar environments. The data presented here may be used for a more detailed study on the pro¯le variations accompanying the mid-IR bands in various interstellar environments.Item Super Massive Black Hole Fundamental Plane for Ellipticals(2007-05-10) Barway, Sudhanshu; Kembhavi, A.K.We obtain the coefficients of a new fundamental plane for supermassive black holes at the centers of elliptical galaxies, involving measured central black hole mass and photometric parameters which define the light distribution. The galaxies are tightly distributed around this mass fundamental plane, with improvement in the rms residual over those obtained from the MBH − σ and MBH − L relations. This implies a strong multidimensional link between the central massive black hole formation and global photometric properties of elliptical galaxies and provides an improved estimate of black hole mass from galaxy data.Item Standing and travelling waves in the shallow-water circular hydraulic jump(2007-08-20) Ray, Arnab K.; Bhattacharjee, Jayanta K.A wave equation for a time-dependent perturbation about the steady shallow-water solution emulates the metric an acoustic white hole, even upon the incorporation of nonlinearity in the lowest order. A standing wave in the sub-critical region of the flow is stabilised by viscosity, and the resulting time scale for the amplitude decay helps in providing a scaling argument for the formation of the hydraulic jump. A standing wave in the super-critical region, on the other hand, displays an unstable character, which, although somewhat mitigated by viscosity, needs nonlinear effects to be saturated. A travelling wave moving upstream from the sub-critical region, destabilises the flow in the vicinity of the jump, for which experimental support has been givenItem Secular instability in quasi-viscous disc accretion(2007-07-12) Bhattacharjee, Jayanta K.; Ray, Arnab K.A first-order correction in the -viscosity parameter of Shakura& Sunyaev has been introduced in the standard inviscid and thin accretion disc. A linearised time-dependent perturbative study of the stationary solutions of this “quasi-viscous” disc leads to the development of a secular instability on large spatial scales. This qualitative feature is equally manifest for two different types of perturbative treatment — a standing wave on subsonic scales, as well as a radially propagating wave. Stability of the flow is restored when viscosity disappears.Item Probing the star formation history using the redshift evolution of luminosity fuctions(2007-03-30) Samui, Saumyadip; Srianand, R.; Subramanian, KandaswamyWe present a self-consistent, semi-analytical ΛCDM model of star formation and reionization. For the cosmological parameters favored by the WMAP data, our models consistently reproduce the electron scattering optical depth to reionization, redshift of reionization and the observed luminosity functions (LF) and hence the star formation rate (SFR) density at 3 ≤ z ≤ 6 for a reasonable range of model parameters. While simple photoionization feedback produces the correct shape of LF at z = 6, for z = 3 we need additional feedback that suppresses star formation activities in halos with 1010 . (M/M⊙) . 1011. Models with prolonged continuous star formation activities are preferred over those with short bursts as they are consistent with the existence of a Balmer break in considerable fraction of observed galaxies even at z ∼ 6. The halo number density evolution from the standard ΛCDMstructure formation model that fits LF up to z = 6 is consistent with the upper limits on z ≃ 7 LF and source counts at 8 ≤ z ≤ 12 obtained fromthe Hubble Ultra Deep Field (HUDF) observations without requiring any dramatic change in the nature of star formation. However, to reproduce the observed LF at 6 ≤ z ≤ 10, obtained from the near-IR observations around strong lensing clusters, we need a strong evolution in the initial mass function, reddening correction and the mode of star formation at z & 8. We show that low mass molecular cooled halos, which may be important for reionizing the universe, are not detectable in the present deep field observations even if a considerable fraction of its baryonic mass goes through a star burst phase. However, their presence and contribution to reionization can be inferred indirectly from the redshift evolution of the luminosity function in the redshift range 6 ≤ z ≤ 12. In our model calculations, the contribution of low mass halos to global SFR density prior to reionization reveals itself in the form of second peak at z ≥ 6. However this peak will not be visible in the observed SFR density as a function of z as most of these galaxies have luminosity below the detection threshold of various ongoing deep field surveys. Accurately measuring the LF at high redshifts can be used to understand the nature of star formation in the dark ages and probe the history of reionization.Item Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011(2007-03-29) Noterdaeme, P.; Srianand, R.; Petitjean, Patrick; et al.Aims. We aim at deriving the physical conditions in the neutral gas associated with damped Lyman-α systems using observation and analysis of H2 and C absorptions. Methods. We obtained a high-resolution VLT-UVES spectrum of the quasar Q2348−011 over a wavelength range that covers most of the prominent metal and molecular absorption lines from the log N(H ) = 20.50±0.10 damped Lyman-α system at zabs = 2.4263. We detected H2 in this system and measured column densities of H2, C , C ∗, C∗∗ , Si , P , S , Fe , and Ni . From the column density ratios and, in particular, the relative populations of H2 rotational and C fine-structure levels, we derived the physical conditions in the gas (relative abundances, dust-depletion, particle density, kinetic temperature, and ionising flux) and discuss physical conditions in the neutral phase. Results. Molecular hydrogen was detected in seven components in the first four rotational levels (J = 0-3) of the vibrational ground state. Absorption lines of H2 J = 4 (resp. J = 5) rotational levels are detected in six (resp. two) of these components. This leads to a total molecular fraction of log f ≃ −1.69+0.37 −0.58. Fourteen components are needed to reproduce the metal-line profiles. The overall metallicity is found to be −0.80, −0.62, −1.17±0.10 for, respectively, [Si/H], [S/H] and [Fe/H]. We confirm the earlier findings that there is a correlation between log N(Fe )/N(S ) and log N(Si )/N(S ) from different components indicative of a dust-depletion pattern. Surprisingly, however, the depletion of metals onto dust in the H2 components is not large in this system: [Fe/S] = −0.8 to −0.1. The gas in H2-bearing components is found to be cold but still hotter than similar gas in our Galaxy (T > 130 K, instead of typically 80 K) and dense (n ∼ 100 − 200 cm−3 ). There is an anti-correlation (R = −0.97) between the logarithm of the photo-absorption rate, log β0, and log N(H2)/N(C ) derived for each H2 component. We show that this is mostly due to shielding effects and imply that the photo-absorption rate β0 is a good indicator of the physical conditions in the gas. We find that the gas is immersed in an intense UV field, about one order of magnitude higher than in the solar vicinity. These results suggest that the gas in H2-bearing DLAs is clumpy, and star-formation occurs in the associated object