2001 (IPP)
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Item R=O spacetimes and self-dual lorentzian wormholes(2001-04-02) Dadhich, Naresh; Kar, Sayan; Mukherjee, Sailajananda; et al.A two–parameter family of spherically symmetric, static Lorentzian wormholes is obtained as the general solution of the equation ρ = ρt = 0, where ρ = Tij ui uj , ρt = (Tij − 1 2T gij ) ui uj , and ui ui = −1. This equation characterizes a class of spacetimes which are “self dual” (in the sense of electrogravity duality). The class includes the Schwarzschild black hole, a family of naked singularities, and a disjoint family of Lorentzian wormholes, all of which have vanishing scalar curvature (R = 0). Properties of these spacetimes are discussed. Using isotropic coordinates we delineate clearly the domains of parameter space for which wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be obtained. A model for the required “exotic” stress–energy is discussed, and the notion of traversability for the wormholes is also examined.Item Star formation losses due to tidal debris in `hierarchical' galaxy formation(2001-07-05) Roukema, B. F.; Ninin, S.; Devriendt, J.; et al.N-body studies have previously shown that the bottom-up hierarchical formation of dark matter haloes is not as monotonic as implicitly assumed in the Press-Schechter formalism. During and following halo mergers, matter can be ejected into tidal tails, shells or low density ‘atmospheres’ outside of the successor haloes’ viriali- sation radii (or group-finder outermost radii). The implications that the possible truncation of star formation in these tidal ‘debris’ may have for observational galaxy statistics are examined here using the ArFus N-body plus semi-analytical galaxy modelling software for standard star formation hypotheses. In the N-body simulations studied, the debris typically remain close to the successor halo and fall back into the successor haloes given sufficient time. A maximum debris loss of around 16% is found for redshift intervals of around ∆z = 0.4 at z ∼ 1, with little dependence on the matter density parameter Ω0 and the cosmological constant λ0. Upper and lower bounds on stellar losses implied by a given set of N-body simulation output data can be investi- gated by choice of the merging/identity criterion of haloes between successive N-body simulation output times. A median merging/identity criterion is defined and used to deduce an upper estimate of possible star formation and stellar population losses. A largest successor merging/identity criterion is defined to deduce an estimate which minimises stellar losses. The losses for star formation and luminosity functions are strongest for low luminosity galaxies — a likely con- sequence of the fact that the debris fraction is highest for low mass haloes — and at intermediate redshifts (1 < ∼z < ∼3). The losses in both cases are mostly around 10%-30%, have some dependence on Ω0 and negligible dependence on λ0. This upper bound on likely losses in star formation rates and stellar populations is smaller than the uncertainties in estimates of corresponding observational parameters. Hence, it may not be urgent to include a correction for this in Press-Schechter based galaxy formation models, except when statistics regarding dwarf galaxies are under study.Item Extended hierarchical search (EHS) algorithm for detection of gravitational waves from inspiraling compact binaries(2001-04-01) Sengupta, Anand; Dhurandhar, Sanjeev; Lazzarini, Albert; et al.Pattern matching techniques like matched filtering will be used for online extraction of gravitational wave signals buried inside detector noise. This involves cross correlating the detector output with hundreds of thousands of templates spanning a multi-dimensional parameter space, which is very expensive computationally. A faster implementation algorithm was devised by Mohanty and Dhurandhar [1996] using a hierarchy of templates over the mass parameters, which speeded up the procedure by about 25 to 30 times. We show that a further reduction in computational cost is possible if we extend the hierarchy paradigm to an extra parameter, namely, the time of arrival of the signal. In the first stage, the chirp waveform is cut-off at a relatively low frequency allowing the data to be coarsely sampled leading to cost saving in performing the FFTs. This is possible because most of the signal power is at low frequencies, and therefore the advantage due to hierarchy over masses is not compromised. Results are obtained for spin-less templates up to the second post-Newtonian (2PN) order for a single detector with LIGO I noise power spectral density. We estimate that the gain in computational cost over a flat search is about 100.Item European large area ISO survey VI - discovery of a new hyperluminous infrared galaxy(2001-09-01) Efstathiou, A.; Efstathiou, A.; Serjeant, S.; et al.We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15, and 90 µm, and is found to be a broad-line, radio-quiet quasar at a redshift: z = 1.099. From a detailed multi-component model fit of the spectral energy distribution, we derive a total IR luminosity: LIR (1-1000 µm) ≈ 1.0 × 1013 h−2 65 L⊙ (q0 = 0.5), and discuss the possible existence of a starburst contributing to the far-IR output. Observations to date present no evidence for lens magnification. This galaxy is one of the very few HyLIGs with an X-ray detection. On the basis of its soft X-ray properties, we suggest that this broad-line object may be the face-on analogue of narrow-line, Seyfert-like HyLIGsItem Cosmic Microwave Background Anisotropy Measurement from Python V(2001-03-01) Coble, Kim; Dodelson, S.; Dragovan, Mark; et al.We analyze observations of the microwave sky made with the Python exper- iment in its fifth year of operation at the Amundsen-Scott South Pole Station in Antarctica. After modeling the noise and constructing a map, we extract the cosmic signal from the data. We simultaneously estimate the angular power spectrum in eight bands ranging from large (ℓ ∼ 40) to small (ℓ ∼ 260) angular scales, with power detected in the first six bands. There is a significant rise in the power spectrum from large to smaller (ℓ ∼ 200) scales, consistent with that ex- pected from acoustic oscillations in the early Universe. We compare this Python V map to a map made from data taken in the third year of Python. Python III observations were made at a frequency of 90 GHz and covered a subset of the region of the sky covered by Python V observations, which were made at 40 GHz. Good agreement is obtained both visually (with a filtered version of the map) and via a likelihood ratio test.Item Binned cosmic microwave background anisotropy power spectra : Peak location(2001-02-15) Podariu, Silviu; Souradeep, Tarun; Gott, J. Richard; et al.We use weighted mean and median statistics techniques to combine individual cosmic microwave background (CMB) anisotropy detections and determine binned, multipole- space, CMB anisotropy power spectra. The resultant power spectra are peaked. The derived weighted-mean CMB anisotropy power spectrum is not a good representation of the individual measurements in a number of multipole-space bins, if the CMB anisotropy is Gaussian and correlations between individual measurements are small. This could mean that some observational error bars are underestimated, possibly as a consequence of undetected systematic effects. Discarding the most discrepant 5% of the measure- ments alleviates but does not completely resolve this problem. The median-statistics power spectrum of this culled data set is not as constraining as the weighted-mean power spectrum. Nevertheless it indicates that there is more power at multipoles ℓ ∼ 150 − 250 than is expected in an open cold dark matter (CDM) model, and it is more consistent with a flat CDM model. Unlike the weighted-mean power spectrum, the median-statistics power spectrum at ℓ ∼ 400 − 500 does not exclude a second peak in the flat CDM model.