8,072 research outputs found
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
Comparison Principles for subelliptic equations of Monge-Ampere type
We present two comparison principles for viscosity sub- and supersolutions of
Monge-Ampere-type equations associated to a family of vector fields. In
particular, we obtain the uniqueness of a viscosity solution to the Dirichlet
problem for the equation of prescribed horizontal Gauss curvature in a Carnot
group
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
Regularity of Nash payoffs of Markovian nonzero-sum stochastic differential games
In this paper we deal with the problem of existence of a smooth solution of
the Hamilton-Jacobi-Bellman-Isaacs (HJBI for short) system of equations
associated with nonzero-sum stochastic differential games. We consider the
problem in unbounded domains either in the case of continuous generators or for
discontinuous ones. In each case we show the existence of a smooth solution of
the system. As a consequence, we show that the game has smooth Nash payoffs
which are given by means of the solution of the HJBI system and the stochastic
process which governs the dynamic of the controlled system.Comment: To appear in "Stochastic
Observational clues to the progenitors of Type-Ia supernovae
Type-Ia supernovae (SNe Ia) are important distance indicators, element
factories, cosmic-ray accelerators, kinetic-energy sources in galaxy evolution,
and endpoints of stellar binary evolution. It has long been clear that a SN Ia
must be the runaway thermonuclear explosion of a degenerate carbon-oxygen
stellar core, most likely a white dwarf (WD). However, the specific progenitor
systems of SNe Ia, and the processes that lead to their ignition, have not been
identified. Two broad classes of progenitor binary systems have long been
considered: single-degenerate (SD), in which a WD gains mass from a
non-degenerate star; and double-degenerate (DD), involving the merger of two
WDs. New theoretical work has enriched these possibilities with some
interesting updates and variants. We review the significant recent
observational progress in addressing the progenitor problem. We consider clues
that have emerged from the observed properties of the various proposed
progenitor populations, from studies of their sites, pre- and post-explosion,
from analysis of the explosions themselves, and from the measurement of event
rates. The recent nearby and well-studied event, SN 2011fe, has been
particularly revealing. The observational results are not yet conclusive, and
sometimes prone to competing theoretical interpretations. Nevertheless, it
appears that DD progenitors, long considered the underdog option, could be
behind some, if not all, SNe Ia. We point to some directions that may lead to
future progress.Comment: to appear in Annual Reviews of Astronomy and Astrophysics, 2014. For
near-final published version see
http://www.annualreviews.org/doi/abs/10.1146/annurev-astro-082812-14103
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