Environment of The Gamma-Ray Burst GRB971214 : A Giant H II Region surrounded by A Galactic Supershell

Among a number of gamma ray bursts whose host galaxies are known, GRB971214 stands out for its high redshift $z\ge 3$ and the Ly$\alpha$ emission line having a P-Cygni type profile, which is interpreted to be a direct consequence of the expanding supershell. From a profile fitting analysis we estimate the expansion velocity of the supershell v_{exp} = 1500\kms and the neutral column density N_{HI}=10^{20}\cm^{-2}. The redshift $z=3.418$ of the host galaxy proposed by Kulkarni et al. (1998) has been revised to be $z=3.425$ from our profile analysis. The observed Ly$\alpha$ profile is fitted well by a Gaussian curve, which yields the Ly$\alpha$ luminosity L_{Ly\alpha}=(1.8\pm0.8)\times10^{42}\ergs \s^{-1}. Assuming that the photon source is a giant H II region, we deduce the electron number density in the H II region n_e=(40\pm10) ({R \over {100 \pc}})^{-1.5}\cm^{-3}, which corresponds to the illumination by about $10^4$ O5 stars. We estimate the star-formation rate to be R_{SF} = (7\pm3){\rm M}_\odot\yr^{-1} with the internal and the Galactic extinction corrected. The theory on the evolution of supernova remnants is used to propose that the supershell is at the adiabatic phase, with its radius R = 18 E_{53}^{1/2} \pc, its age $t = 4.7\times10^3\ E_{53}^{1/2} \yrs$, and the density of the ambient medium$n_1 = 5.4\ E_{53}^{-1/2}\cm^{-3}$, where$E_{53}= E/10^{53}\ergs$.And we estimate the kinetic energy of the supershell to be$E_k=7.3\times10^{52} E_{53} \ergs$. These values are consistent with the hypothesis that the supershell is the remnant of a gamma ray burst.Comment: 5 papges, 3 figures, Accepted for publication in Astrophysical Journal Letter

Constraining Ω0{\Omega_{0}} from X-ray properties of Clusters of Galaxies at high redshift

Properties of high redshift clusters are a fundamental source of information for cosmology. It has been shown by Oukbir and Blanchard (1997) that the combined knowledge of the redshift distribution of X-ray clusters of galaxies and the luminosity-temperature correlation, $L_X-T_X$, provides a powerful test of the mean density of the Universe. In this paper, we address the question of the possible evolution of this relation from an observational point of view and its cosmological significance. We introduce a new indicator in order to measure the evolution of the X-ray luminosity-temperature relation with redshift and take advantage of the recent availability of temperature information for a significant number of high and intermediate redshift X-ray clusters of galaxies. From our analysis, we find a slightly positive evolution in the $L_X-T_X$ relation. This implies a high value of the density parameter of $0.85\pm0.2$. However, because the selection of clusters included inour sample is unknown, this can be considered only as a tentative result. A well-controlled X-ray selected survey would provide a more robust answer. XMM will be ideal for such a program.Comment: 10 pages, LaTeX, 4 figures,5 tables, accepted by A&

Supernova pencil beam survey

Type Ia supernovae (SNe Ia) can be calibrated to be good standard candles at cosmological distances. We propose a supernova pencil beam survey that could yield between dozens to hundreds of SNe Ia in redshift bins of 0.1 up to $z=1.5$, which would compliment space based SN searches, and enable the proper consideration of the systematic uncertainties of SNe Ia as standard candles, in particular, luminosity evolution and gravitational lensing. We simulate SNe Ia luminosities by adding weak lensing noise (using empirical fitting formulae) and scatter in SN Ia absolute magnitudes to standard candles placed at random redshifts. We show that flux-averaging is powerful in reducing the combined noise due to gravitational lensing and scatter in SN Ia absolute magnitudes. The SN number count is not sensitive to matter distribution in the universe; it can be used to test models of cosmology or to measure the SN rate. The SN pencil beam survey can yield a wealth of data which should enable accurate determination of the cosmological parameters and the SN rate, and provide valuable information on the formation and evolution of galaxies. The SN pencil beam survey can be accomplished on a dedicated 4 meter telescope with a square degree field of view. This telescope can be used to conduct other important observational projects compatible with the SN pencil beam survey, such as QSOs, Kuiper belt objects, and in particular, weak lensing measurements of field galaxies, and the search for gamma-ray burst afterglows.Comment: Final version, to appear in ApJ, 531, #2 (March 10, 2000). 22 pages including 5 figures. Improved presentatio

Galaxy Modelling -- I. Spectral Energy Distributions from Far-UV to Sub-mm Wavelengths

(abridged) We present STARDUST, a new self-consistent modelling of the spectral energy distributions (SEDs) of galaxies from far-UV to radio wavelengths. In order to derive the SEDs in this broad spectral range, we first couple spectrophotometric and (closed-box) chemical evolutions to account for metallicity effects on the spectra of synthetic stellar populations. We then use a phenomenological fit for the metal-dependent extinction curve and a simple geometric distribution of the dust to compute the optical depth of galaxies and the corresponding obscuration curve. This enables us to calculate the fraction of stellar light reprocessed in the infrared range. In a final step, we define a dust model with various components and we fix the weights of these components in order to reproduce the IRAS correlation of IR colours with total IR luminosities. This allows us to compute far-IR SEDs that phenomenologically mimic observed trends. We are able to predict the spectral evolution of galaxies in a broad wavelength range, and we can reproduce the observed SEDs of local spirals, starbursts, luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs). This modelling is so far kept as simple as possible and depends on a small number of free parameters, namely the initial mass function (IMF), star formation rate (SFR) time scale, gas density, and galaxy age, as well as on more refined assumptions on dust properties and the presence (or absence) of gas inflows/outflows.Comment: 20 pages, 23 figures, Accepted for publication in Astronomy and Astrophysics Main Journa