Type Ia supernova counts at high z: signatures of cosmological models and progenitors

Determination of the rates at which supernovae of Type Ia (SNe Ia) occur in the early Universe can give signatures of the time spent by the binary progenitor systems to reach explosion and of the geometry of the Universe. Observations made within the Supernova Cosmology Project are already providing the first numbers. Here it is shown that, for any assumed SNe Ia progenitor, SNe Ia counts up to $m_{R}\simeq 23-26$ are useful tests of the SNe Ia progenitor systems and cosmological tracers of a possible non-zero value of the cosmological constant, $\Lambda$. The SNe Ia counts at high redshifts compare differently with those at lower redshifts depending on the cosmological model. Flat $\Omega_{\Lambda}$--dominated universes would show a more significant increase of the SNe Ia counts at $z \sim 1$ than a flat, $\Omega_{M} = 1$ universe. Here we consider three sorts of universes: a flat universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $\Omega_{M} = 1.0$, $\Omega_{\Lambda} = 0.0$; an open universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $\Omega_{M} = 0.3$, $\Omega_{\Lambda} = 0.0$; and a flat, $\Lambda$--dominated universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $\Omega_{M} = 0.3$, $\Omega_{\Lambda} = 0.7$). On the other hand, the SNe Ia counts from one class of binary progenitors (double degenerate systems) should not increase steeply in the $z= 0$ to $z= 1$ range, contrary to what should be seen for other binary progenitors. A measurement of the SNe Ia counts up to $z \sim 1$ is within reach of ongoing SNe Ia searches at high redshifts.Comment: 16 pages, incl. 2 figures. To appear in ApJ (Letters

The H-alpha and Infrared Star Formation Rates for the Nearby Field Galaxy Survey

We investigate the H-alpha and infrared star formation rate (SFR) diagnostics for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in our sample, we derive H-alpha fluxes (included here) from integrated spectra. There is a strong correlation between the ratio of far-infrared to optical luminosities L(FIR)/L(H-alpha) and the extinction E(B-V) measured with the Balmer decrement. Before reddening correction, the SFR(IR) and SFR(H-alpha) are related to each other by a power-law. Correction of the SFR(H-alpha) for extinction using the Balmer decrement and a classical reddening curve both reduces the scatter in the SFR(IR)-SFR(H-alpha) correlation and results in a much closer agreement (within ~10%) between the two SFR indicators. This SFR relationship spans 4 orders of magnitude and holds for all Hubble types with IRAS detections in the NFGS. A constant ratio between the SFR(IR) and SFR(H-alpha) for all Hubble types, including early types (S0-Sab), suggests that the IR emission in all of these objects results from a young stellar population.Comment: 23 pages, 5 figures, 1 table. Accepted for publication in the Astronomical Journal. V2: Important changes: IRAS fluxes updated. Only moderate and good quality IRAS FIR fluxes are now used, resulting in slight changes to the equations and figures. The IR and H-alpha SFRs now agree to within ~10%, rather than ~30% as quoted previousl

Radiation induced warping of protostellar accretion disks

We examine the consequences of radiatively driven warping of accretion disks surrounding pre-main-sequence stars. These disks are stable against warping if the luminosity arises from a steady accretion flow, but are unstable at late times when the intrinsic luminosity of the star overwhelms that provided by the disk. Warps can be excited for stars with luminosities of around 10 solar luminosities or greater, with larger and more severe warps in the more luminous systems. A twisted inner disk may lead to high extinction towards stars often viewed through their disks. After the disk at all radii becomes optically thin, the warp decays gradually on the local viscous timescale, which is likely to be long. We suggest that radiation induced warping may account for the origin of the warped dust disk seen in Beta Pictoris, if the star is only around 10-20 Myr old, and could lead to non-coplanar planetary systems around higher mass stars.Comment: 12 pages, including 3 figures. ApJ Letters, in pres

NICMOS Snapshot Survey of Damped Lyman Alpha Quasars

We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5 sigma detection limits of ~H=22 in the majority of our images. We compare our observations to the observed Lyman-break population of high-redshift galaxies, as well as Bruzual & Charlot evolutionary models of present-day galaxies redshifted to the distances of the absorption systems. We predict H magnitudes for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy (LBG) at their redshift. Comparing these predictions to our sensitivity, we find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most of our observations. We find only one new possible candidate, that near LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most DLA systems are not drawn from a normal LBG luminosity function nor a local galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap

Apparatus for dimensional characterization of fused silica fibers for the suspensions of advanced gravitational wave detectors

Detection of gravitational waves from astrophysical sources remains one of the most challenging problems faced by experimental physicists. A significant limit to the sensitivity of future long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test mass mirrors and their suspensions. Suspension thermal noise results from mechanical dissipation in the fused silica suspension fibers suspending the test mass mirrors and is therefore an important noise source at operating frequencies between ∼10 and 30 Hz. This dissipation occurs due to a combination of thermoelastic damping, surface and bulk losses. Its effects can be reduced by optimizing the thermoelastic and surface loss, and these parameters are a function of the cross sectional dimensions of the fiber along its length. This paper presents a new apparatus capable of high resolution measurements of the cross sectional dimensions of suspension fibers of both rectangular and circular cross section, suitable for use in advanced detector mirror suspensions

A General Formulation of the Source Confusion Statistics and Application to Infrared Galaxy Surveys

Source confusion has been a long-standing problem in the astronomical history. In the previous formulation, sources are assumed to be distributed homogeneously on the sky. This fundamental assumption is not realistic in many applications. In this work, by making use of the point field theory, we derive general analytic formulae for the confusion problems with arbitrary distribution and correlation functions. As a typical example, we apply these new formulae to the source confusion of infrared galaxies. We first calculate the confusion statistics for power-law galaxy number counts as a test case. When the slope of differential number counts, \gamma, is steep, the confusion limits becomes much brighter and the probability distribution function (PDF) of the fluctuation field is strongly distorted. Then we estimate the PDF and confusion limits based on the realistic number count model for infrared galaxies. The gradual flattening of the slope of the source counts makes the clustering effect rather mild. Clustering effects result in an increase of the limiting flux density with \sim 10%. In this case, the peak probability of the PDF decreases up to \sim 15% and its tail becomes heavier.Comment: ApJ in press, 21 pages, 9 figures, using aastex.cls, emulateapj5.sty. Abstract abridge

Experimental results for nulling the effective thermal expansion coefficient of fused silica fibres under a static stress

We have experimentally demonstrated that the effective thermal expansion coefficient of a fused silica fibre can be nulled by placing the fibre under a particular level of stress. Our technique involves heating the fibre and measuring how the fibre length changes with temperature as the stress on the fibre was systematically varied. This nulling of the effective thermal expansion coefficient should allow for the complete elimination of thermoelastic noise and is essential for allowing second generation gravitational wave detectors to reach their target sensitivity. To our knowledge this is the first time that the cancelation of the thermal expansion coefficient with stress has been experimentally observed

A 43-GHz Survey in the ELAIS N2 Area

We describe a survey in the ELAIS N2 region with the VLA at 43.4 GHz, carried out with 1627 independent snapshot observations in D-configuration and covering about 0.5 square degrees. One certain source is detected, a previously-catalogued flat-spectrum QSO at z=2.2. A few (<5) other sources may be present at about the 3sigma level, as determined from positions of source-like deflections coinciding with blue stellar objects, or with sources from lower-frequency surveys. Independently we show how all the source-like detections identified in the data can be used with a maximum-likelihood technique to constrain the 43-GHz source counts at a level of ~7 mJy. Previous estimates of the counts at 43 GHz, based on lower-frequency counts and spectral measurements, are consistent with these constraints, although the present results are suggestive of somewhat higher surface densities at the 7 mJy level. They do not provide direct evidence of intrusion of a previously unknown source population, although the several candidate sources need examination before such a population can be ruled out.Comment: 13 pages, 11 figures, 1 table; accepted for publication in Mon. Not R. Astr. So

The Evolution of Dust Opacity in Galaxies

(Abridged) We investigate the evolution of the opacity of galaxies as a function of redshift, using simple assumptions about the metal and dust enrichment of the gas and the distribution of dust in galaxies. We use an iterative procedure to reconstruct the intrinsic Star Formation Rate (SFR) density of galaxies with redshift, by applying dust obscuration corrections to the observed UV emission. The iterative procedure converges to multiple solutions for the intrinsic SFR density, divided into two basic classes. The first class of solutions predicts relatively large UV attenuation at high redshift, with A(1500 A)=1.9 mag at z~3, and smaller attenuations at z<1, with A(2800 A)=1.25 mag. The SFR density of this set of solutions is constant for z>~1.2 and declines for z<1.2; it resembles in shape the ``monolithic collapse'' scenario for star formation. The second class of solutions predicts relatively low UV attenuations at high redshift, with A(1500 A)=0.75 mag at z~3, and larger attenuations at z<1, with A(2800 A)=1.50 mag. The SFR density in this case has a peak at z~1.2. The advantages and shortcomings of both classes are analyzed in the light of available observational constraints, including the opacity of galaxies at 0<z<1 and the intensity and spectral energy distribution of the cosmic infrared background from the COBE DIRBE and FIRAS data. We conclude that both classes of models are acceptable within the current uncertainties, but the ``monolithic collapse'' class matches the available observations better than the other one. We also investigate the dependence of our solutions on the different model assumptions.Comment: 54 pages, includes 1 embedded postscript Table and 22 embedded postscript Figures, Latex, uses AAS Latex macro. Accepted for publication in the Astrophysical Journa

Cryogenic and room temperature strength of sapphire jointed by hydroxide-catalysis bonding

Hydroxide-catalysis bonding is a precision technique used for jointing components in opto-mechanical systems and has been implemented in the construction of quasi-monolithic silica suspensions in gravitational wave detectors. Future detectors are likely to operate at cryogenic temperatures which will lead to a change in test mass and suspension material. One candidate material is mono-crystalline sapphire. Here results are presented showing the influence of various bonding solutions on the strength of the hydroxide-catalysis bonds formed between sapphire samples, measured both at room temperature and at 77 K, and it is demonstrated that sodium silicate solution is the most promising in terms of strength, producing bonds with a mean strength of 63 MPa. In addition the results show that the strengths of bonds were undiminished when tested at cryogenic temperatures