2010 (IPP)
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Item Optical spectroscopy of candidates of young stellar objects in NGC 1333(2010-12-31) Itoh, Yoichi; et al.; Gupta, Ranjan; Oasa, YumikoWe carried out low-resolution optical spectroscopy of 14 low-luminosity young stellar object (YSO) candidates in the NGC 1333 cluster. These objects were previously identified by the near-infrared imaging survey. Eleven objects were confirmed as YSOs by the H line emission. Strengths of the H emission are correlated with the near-infrared excesses of the objects. Spectral types of all YSOs are estimated to be M-type, indicative of low-mass. Comparisons of the results of our spectroscopic observations and the previous photometric observations with evolutionary tracks on the HR diagram suggest two objects to be young brown dwarfs.Item Turbulence modeling and the physics of the Intra-cluster medium(2010-07-11) Niemeyer, Jens C.; Paul, Surajit; et al.; Iapichino, L.The effective modeling of the stirring and development of turbulent flows in grid-based hydrodynamical simulations is computationally challenging. Here we present two possible ways to tackle the problem: first, we consider the use of the adaptive mesh refinement (AMR), applying novel refinement criteria which are optimized to follow the evolution of a turbulent flow. In a second step, the AMR is combined with a subgrid scale (SGS) model for the unresolved turbulence, thus resulting in a new numerical technique called FEARLESS (Fluid mEchanics with Adaptively Refined Large Eddy SimulationS). FEARLESS performs both the adaptive refinement of the regions where turbulent flows develop and a consistent coupling of the SGS turbulence with the resolved scales, and is argued to be a suitable tool in simulations of turbulent clumped flows. The results of galaxy cluster simulations, performed with the new tool, give rise to several interesting implications with regard to the physics of these objects, and to the numerical methods employed for their exploration in computational cosmology.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 Primordial features due to a step in the inflaton potential(2010-05-12) Hazra, Dhiraj Kumar; et al.; Aich, Moumita; Jain, Rajeev KumarCertain oscillatory features in the primordial scalar power spectrum are known to provide a better fit to the outliers in the cosmic microwave background data near the multipole moments of ℓ = 22 and 40. These features are usually generated by introducing a step in the popular, quadratic potential describing the canonical scalar field. Such a model will be ruled out, if the tensors remain undetected at a level corresponding to a tensor-to-scalar ratio of, say, r ≃ 0.1. In this work, in addition to the popular quadratic potential, we investigate the effects of the step in a small field model and a tachyon model. With possible applications to future datasets (such as PLANCK) in mind, we evaluate the tensor power spectrum exactly, and include its contribution in our analysis. We compare the models with the WMAP (five as well as seven-year), the QUaD and the ACBAR data. As expected, a step at a particular location and of a suitable magnitude and width is found to improve the fit to the outliers (near ℓ = 22 and 40) in all these cases. We point out that, if the tensors prove to be small (say, r . 0.01), the quadratic potential and the tachyon model will cease to be viable, and more attention will need to be paid to examples such as the small field models.Item Polarimetric observations of comet 67P/Churyumov-gerasimenko during its 2008-2009 apparition(2010-04-01) Hadamcik, E.; et al.; Sen, A.K.; Levasseur-Regourd, A. C.Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dustcoma are of major importance to determine the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow a comparison between di erent coma regions and di erent comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Methods. Recent imaging polarimetric observations have been conducted at Haute-Provence observatory (France) on 2009 March 17-19 at 35° phase angle and at IUCAA Girawali observatory (India) on 2008 December 25-27 at 36° phase angle and on 2009 April 30-May 1 at 29° phase angle. With the imaging technique, the intensity and linear polarization variations are studied through the various coma regions. These observations are compared to other cometary data (e.g.Jupiter family comets) and to numerical and experimental simulations. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to -1, although important variations with values down to -1.5 are noticed, in agreement with previous observations in 1982-83 and 1995-96. The intensity along the tailward direction decreases with a slope between -1.2 two months before perihelion (2009 February 28)to -1.0 two months after perihelion; the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any di erence in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron- or submicron-sized grains. Conclusions. Polarization and intensity variations in the coma of 67P/Churyumov-Gerasimenko are reminiscent of those noticed for some comets such as comet 81P/Wild 2 and comet 9P/Tempel 1. The presence of rather large particles can thus be suggested before and just after perihelion and the ejection of smaller grains, eventually in flu y aggregates post-perihelion. An important sea-sonal e ect related to the obliquity of the comet suggests that the di erent grains originate from di erent hemispheres of the nucleus.Item Photopolarimetric study of the star-forming clouds CB3,CB25,and CB39(2010-07-22) Sen, A.K.; et al.; Polcaro, V. F.; Dey, I.The small compact isolated dark clouds also known as ’Bok globules’ are believed to be ideal sites for low-mass star formation. Some of these clouds are undergoing gravitational collapse, and the ambient magnetic field plays a key role in collapse dynamics. The background star polarimetry is generally accepted as a good tool to map the magnetic field, which is responsible for the alignment of dichroic grains that produce polarization. Aims. The background star polarization when studied together with extinction is expected to help us to understand various grain properties and the role of polarimetry as a tracer of magnetic field in these star-forming clouds. With this idea, polarization and colour excess E(B − V ) values for a set of background stars have been studied together to understand various astrophysical process in some star-forming dark clouds. Methods. Optical photometric observations of the three clouds CB3, CB25, and CB39 were carried out at the 2m H.C. Telescope, India, to determine the colour excess E(B −V ) of the background stars by following a technique adopted by Barnei and Polacaro (2001). These three clouds were selected from a set of eight clouds previously observed by us in optical polarimetry ( Sen et al. 2000). Further independent spectroscopic measurements of a few selected sample stars were recently carried out during February and March 2010 from 1.52m Cassini Telescope, Loinao, Italy, to confirm the correctness of estimated E(B − V ) values obtained by this photometric technique. Results. The colour excess E(B−V ) values so obtained were compared with optical polarization values obtained for the same set of stars. It was found that the measured extinction values increase with the increase in percentage polarization for the cloud CB39 and to some extent for CB25. However, for cloud CB31 no such correlation was observed. It is normally expected that the grains causing extinction should also cause polarization of the light from background stars. Any possible deviation from this under different circumstances here has been discussed in the light of the ongoing physical processes in the star-forming clouds.Item GMRT mini-survey to search for 21-cm absorption in quasar-galaxy pairs at z~0.1(2010-07-05) Gupta, N.; et al.; Srianand, R.We present the results from our 21-cm absorption survey of a sample of 5 quasar-galaxy pairs (QGPs), with the redshift of the galaxies in the range 0.03≤ zg ≤ 0.18, selected from the Sloan Digital Sky Survey (SDSS). The H i 21-cm absorption was searched towards the 9 sight lines with impact parameters ranging from ∼10 to ∼55 kpc using Giant Metrewave Radio Telescope (GMRT). 21-cm absorption was detected only in one case i.e. towards the Quasar (zq = 2.625SDSS J124157.54+633241.6) − galaxy (zg = 0.143 SDSS J124157.26+633237.6) pair with the impact parameter ∼11 kpc. The quasar sight line in this case pierces through the stellar disk of a galaxy having near solar metallicity (i.e (O/H)+12 = 8.7) and star formation rate uncorrected for dust attenuation of 0.1M⊙ yr−1. The quasar spectrum reddened by the foreground galaxy is well fitted with the Milky Way extinction curve (with an AV of 0.44) and the estimated H i column density is similar to the value obtained from 21-cm absorption assuming spin temperature (TS) of 100K. In the remaining cases, our GMRT spectra provide upper limit on N(H i) in the range, (1017 −1018)×TS cm−2. Combining our sample with the z ≤ 0.1 data available in the literature, we find the detectability of 21-cm absorption with integrated optical depth greater than 0.1 kms−1 to be 50% for the impact parameter less than 20 kpc. Using the surface brightness profiles and well established relationship between the optical size and extent of the H i disk known for nearby galaxies, we conclude that in most of the cases of 21-cm absorption non-detection, the sight lines may not be passing through the H i gas (1σ column density of few times 1019 cm−2). We also find that in comparison to the absorption systems associated with these QGPs, z < 1 DLAs with 21-cm absorption detections have lower Ca ii equivalent widths despite having higher 21-cm optical depths and smaller impact parameters. This suggests that the current sample of DLAs may be a biased population that avoids sight lines through dusty star-forming galaxies. A systematic survey of QGPs over a wider redshift range using a large sample is needed to confirm these findings and understand the nature of 21-cm absorbers.Item Evolution of shocks and turbulence in major cluster mergers(2010-12-14) Paul, Surajit; Iapichino, L.; Miniati, F.; et al.We performed a set of cosmological simulations of major mergers in galaxy clusters, in order to study the evolution of merger shocks and the subsequent injection of turbulence in the post-shock region and in the intra-cluster medium (ICM). The computations have been performed with the grid-based, adaptive mesh refinement (AMR) hydrodynamical code Enzo, using a refinement criterion especially designed for refining turbulent flows in the vicinity of shocks. When a major merger event occurs, a substantial amount of turbulence energy is injected in the ICM of the newly formed cluster. Our simulations show that the shock launched after a major merger develops an ellipsoidal shape and gets broken by the interaction with the filamentary cosmic web around the merging cluster. The size of the post-shock region along the direction of shock propagation is of the order of 300 kpc h−¹, and the turbulent velocity dispersion in this region is larger than 100 km s−¹. We performed a scaling analysis of the turbulence energy within our cluster sample. The best fit for the scaling of the turbulence energy with the cluster mass is consistent with M⁵/³, which is also the scaling law for the thermal energy in the self-similar cluster model. This clearly indicates the close relation between virialization and injection of turbulence in the cluster evolution. As for the turbulence in the cluster core, we found that within 2 Gyr after the major merger (the timescale for the shock propagation in the ICM), the ratio of the turbulent to total pressure is larger than 10%, and after about 4 Gyr it is still larger than 5%, a typical value for nearly relaxed clusters. Turbulence at the cluster center is thus sustained for several Gigayears, which is substantially longer than typically assumed in the turbulent re-accelerationmodels, invoked for explaining the statistics of observed radio halos. Striking similarities in the morphology and other physical parameters between our simulations and the ‘symmetrical radio relics’ found at the periphery of the merging cluster Abell 3376 are finally discussed. In particular, the interaction between the merger shock and the filaments surrounding the cluster could explain the presence of ‘notch-like’ features at the edges of the double relics.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.