2,132 research outputs found
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 z3 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
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