Showing papers by "I. M. Hook published in 1999"

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

Abstract: We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

The unusual afterglow of the γ-ray burst of 26 March 1998 as evidence for a supernova connection

Abstract: Cosmic γ-ray bursts have now been firmly established as one of the most powerful phenomena in the Universe, releasing almost the rest-mass energy of a neutron star within the space of a few seconds (ref. 1). The two most popular models to explain γ-ray bursts are the coalescence of two compact objects such as neutron stars or black holes, or the catastrophic collapse of a massive star in a very energetic supernova-like explosion. Here we show that, about three weeks after the gamma-ray burst of 26 March 1998, the transient optical source associated with the burst brightened to about 60 times the expected flux, based upon an extrapolation of the initial light curve. Moreover, the spectrum changed dramatically, with the colour becoming extremely red. We argue that the new source is an underlying supernova. If our hypothesis is true then this provides evidence linking cosmologically located γ-ray bursts with deaths of massive stars.

ESO Imaging Survey. I. Description of the survey, data reduction and reliability of the data

Abstract: This paper presents the first data evaluation of the ESO Imaging Survey (EIS), a public survey being carried out by ESO and member states, in preparation for the VLT first-light. The survey goals, organization, strategy and observations are discussed and an overview is given of the survey pipeline developed to handle EIS data and produce object catalogs. A report is presented on moderately deep I -band observations obtained in the first of four patches surveyed, covering a region of 3.2 square degrees centered at and . The products available to the community, including pixel maps (with astrometric and photometric calibrations) and the corresponding object catalogs, are also described. In order to evaluate the quality of the data, preliminary estimates are presented for the star and galaxy number counts, and for the angular two-point correlation function obtained from the available data. The present work is meant as a preview of the final release of the EIS data that will become available later this year.

ESO Imaging Survey - IV. Multicolor analysis of point-like objects toward the South Galactic Pole

Abstract: This paper presents preliminary lists of potentially interesting point-like sources extracted from multicolor data obtained for a 1.7 square degree region near the South Galactic Pole. The region has been covered by the ESO Imaging Survey (EIS) in and I and offers a unique combination of area and depth. These lists, containing a total of 330 objects nearly all brighter than , over 1.27 square degrees (after removing some bad regions), are by-products of the process of verification and quality control of the object catalogs being produced. Among the color selected targets are candidate very low mass stars/brown dwarfs (54), white-dwarfs (32), and quasars (244). In addition, a probable fast moving asteroid was identified. The objects presented here are natural candidates for follow-up spectroscopic observations and illustrate the usefulness of the EIS data for a broad range of science and for providing possible samples for the first year of the VLT.

ESO imaging survey. III. Multicolor data near the South Galactic Pole

Abstract: This paper presents multicolor data obtained for a 1.7 square degree region near the South Galactic Pole (patch B) as part of the ESO Imaging Survey (EIS). So far the observations have been conducted in B,V and I but are expected to be complemented by observations in the U band later in 1998. Object catalogs extracted from single exposure images are 80% complete down to B~24, V~23.5 and I ~22.5 and once coadded should reach about 0.5 mag deeper. The data are being made public in the form of catalogs, pixel maps, target lists and image "postage stamps" which can be retrieved from the Web. Counts of stars and galaxies and the angular two-point correlation function of galaxies are computed and compared to other available data to evaluate the depth and uniformity of the extrtacted object catalogs. In addition, color distributions of stellar objects are presented and compared to model predictions to examine the reliability of the colors. The results suggest that the overall quality of the catalogs extracted from the images is good and suitable for the science goals of the survey.