The Hubble Deep Field Reveals a Supernova at z~0.95

We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which has brightened, during the 8.5 days sampled by the data, by more than 0.9 mag in I and about 0.7 mag in V, remaining stable in B. Subsequent observations of the HDF-N show that two years later this object has dimmed back to about its original brightness in I. The colors of this object, its brightness, its time behavior in the various filters and the evolution of its morphology are consistent with being a Type Ib supernova in a faint galaxy at z~0.95.Comment: 5 pages including 2 figures. Accepted for publication in MNRA

LSD and AMAZE: the mass-metallicity relation at z>3

We present the first results on galaxy metallicity evolution at z>3 from two projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE (Assessing the Mass Abundance redshift Evolution). These projects use deep near-infrared spectroscopic observations of a sample of ~40 LBGs to estimate the gas-phase metallicity from the emission lines. We derive the mass-metallicity relation at z$>$3 and compare it with the same relation at lower redshift. Strong evolution from z=0 and z=2 to z=3 is observed, and this finding puts strong constrains on the models of galaxy evolution. These preliminary results show that the effective oxygen yields does not increase with stellar mass, implying that the simple outflow model does not apply at z>3.Comment: 5 pages, to appear in the IAUS 255 conference proceedings: "Low-Metallicity Star Formation: from the First Stars to Dwarf Galaxies", L.K. Hunt, S. Madden and R. Schneider ed

Two populations of progenitors for type Ia SNe?

We use recent observations of type Ia Supernova (SN Ia) rates to derive, on robust empirical grounds, the distribution of the delay time (DTD) between the formation of the progenitor star and its explosion as a SN. Our analysis finds: i) delay times as long as 3-4 Gyr, derived from observations of SNe Ia at high redshift, cannot reproduce the dependence of the SN Ia rate on the colors and on the radio-luminosity of the parent galaxies, as observed in the local Universe; ii) the comparison between observed SN rates and a grid of theoretical "single-population" DTDs shows that only a few of them are possibly consistent with observations. The most successful models are all predicting a peak of SN explosions soon after star formation and an extended tail in the DTD, and can reproduce the data but only at a modest statistical confidence level; iii) present data are best matched by a bimodal DTD, in which about 50% of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar birth, in a time of the order of 10^8 years, while the remaining 50% ("tardy" SN Ia) have a much wider distribution, well described by an exponential function with a decay time of about 3 Gyr. This fact, coupled with the well established bimodal distribution of the decay rate, suggests the existence of two classes of progenitors. We discuss the cosmological implications of this result and make simple predictions. [Abridged]Comment: 11 pages, MNRAS, in press, modified after referee's comment

A Narrowband Imaging Survey for High Redshift Galaxies in the Near Infrared

A narrowband imaging survey of 276 square minutes of arc was carried out at near infrared wavelengths to search for emission line objects at high redshifts. Most of the fields contained a known quasar or radio galaxy at a redshift that placed one of the strong, restframe optical emission lines (H-alpha, [O III], H-beta, or [O II]) in the bandpass of the narrowband filter. The area weighted line flux limit over the entire survey was 3.4x10e-16 erg/cm2/s (3-sigma), while the most sensitive limits reached 1.4x10e-16 erg/cm2/s. Integrating the volume covered by all four optical emission lines in each image yields a total comoving volume surveyed of 1.4x10e5 cubic megaparsecs. Considering only H-alpha emission in the K band (2.05 < z < 2.65), where the survey is most sensitive, the survey covered a comoving volume of 3.0x10e4 cubic megaparsecs to a volume-weighted average star formation rate of 112 M-solar/yr (for Ho = 50 km/s/Mpc, Omega = 1). This is the most extensive near-infrared survey which is deep enough to have a reasonable chance at detecting strong line emission from an actively star-forming population of galaxies, when d against simple models of galaxy formation. One emission line candidate was identified in this survey, and subsequently confirmed spectroscopically.Comment: To appear in the Astronomical Journal, November 1996. 23 pages, including 2 tables and 7 figure