10,015 research outputs found
The Determination of the Star Formation Rate in Galaxies
A spectrophotometric model able to compute the integrated spectrum of a
galaxy, including the contribution both of the stellar populations and of the
ionized interstellar gas of the HII regions powered by young hot stars, has
been used to study several spectral features and photometric quantities in
order to derive calibrations of the star formation history of late type
galaxies. Attention has been paid to analyze the emission of the Balmer lines
and the [OII]3727 line to test their attitude at providing estimates
of the present star formation rate in galaxies. Other features, like D
and the equivalent width of the H line, influenced by the presence
of intermediate age stars, have been considered. Several ways of estimating the
star formation rates in normal galaxies are discussed and some considerations
concerning the applicability of the models are presented. Criteria have been
also studied for ascertaining the presence of a burst, current or ended not
long ago. Bursts usually hinder the determination of the past star formation
rate.Comment: 21 pages, needs A&A l-aa.sty, accepted for publication in Astronomy &
Astrophysic
An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly
We present an integrated study of star formation and galactic stellar mass
assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9
using a very large and highly spectroscopically complete sample selected by
rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit
Bruzual & Charlot (2003) models to compute the galactic stellar masses and
extinctions. We determine the expected formed stellar mass density growth rates
produced by star formation and compare them with the growth rates measured from
the formed stellar mass functions by mass interval. We show that the growth
rates match if the IMF is slightly increased from the Salpeter IMF at
intermediate masses (~10 solar masses). We investigate the evolution of galaxy
color, spectral type, and morphology with mass and redshift and the evolution
of mass with environment. We find that applying extinction corrections is
critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the
green valley are 24um sources, but after correcting for extinction, the bulk of
the 24um sources lie in the blue cloud. We find an evolution of the
metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex
between the local value and the value at z=0.77 in the 1e10-1e11 solar mass
range. We use the metallicity evolution to estimate the gas mass of the
galaxies, which we compare with the galactic stellar mass assembly and star
formation histories. Overall, our measurements are consistent with a galaxy
evolution process dominated by episodic bursts of star formation and where star
formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5
because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa
Starbursts and the Butcher-Oemler effect in galaxy clusters
In order to explain the spectroscopic observations of most of the galaxies in intermediate redshift clusters, bursts of star formation superimposed to the traditional scenario of galactic evolution are needed. The analysis of spectral lines and colours by means of an evolutionary synthesis model, including both the stellar contribution and the emission of the ionized gas, allows in most of the cases the determination of the time elapsed since the end of the burst and the fraction of galactic mass involved in it. In the four clusters considered (AC103, AC114, AC118 at \rm z=0.31 and Cl1358+6245 at \rm z=0.33), the theoretical analysis demonstrates that the bursts affect substantial galactic mass fractions, typically 30 \% or more. The observations can be equally well reproduced by either elliptical+burst models or by spiral+burst models in which the star formation is truncated at the end of the burst. A way to determine the galactic original type is suggested
Extensions of Superscaling from Relativistic Mean Field Theory: the SuSAv2 Model
We present a systematic analysis of the quasielastic scaling functions
computed within the Relativistic Mean Field (RMF) Theory and we propose an
extension of the SuperScaling Approach (SuSA) model based on these results. The
main aim of this work is to develop a realistic and accurate phenomenological
model (SuSAv2), which incorporates the different RMF effects in the
longitudinal and transverse nuclear responses, as well as in the isovector and
isoscalar channels. This provides a complete set of reference scaling functions
to describe in a consistent way both processes and the
neutrino/antineutrino-nucleus reactions in the quasielastic region. A
comparison of the model predictions with electron and neutrino scattering data
is presented.Comment: 19 pages, 24 figure
Indicators of star formation: 4000 Angstrom break and Balmer lines
The behaviour of the 4000 Angstrom break index and of the equivalent width of
the main Balmer lines is investigated a) for a single star as a function of
effective temperature, gravity and metallicity and b) for a single stellar
population as a function of age and metallicity. Consequences for the
interpretation of integrated spectra are presented.Comment: 5 pages, needs A&A l-aa.sty, accepted for publication in Astronomy &
Astrophysics, complete preprint with figures available on request at
[email protected]
A Search for Nitrogen Enriched Quasars in the Sloan Digital Sky Survey Early Data Release
A search for nitrogen-rich quasars in the Sloan Digital Sky Survey Early Data
Release (SDSS EDR) catalog has yielded 16 candidates, including five with very
prominent emission, but no cases with nitrogen emission as strong as in
Q0353-383. The quasar Q0353-383 has long been known to have extremely strong
nitrogen intercombination lines at lambda 1486 and lambda 1750 Angstroms,
implying an anomalously high nitrogen abundance of about 15 times solar. It is
still the only one of its kind known. A preliminary search through the EDR
using the observed property of the weak C IV emission seen in Q0353-383
resulted in a sample of 23 objects with unusual emission or absorption-line
properties, including one very luminous redshift 2.5 star-forming galaxy. We
present descriptions, preliminary emission-line measurements, and spectra for
all the objects discussed here.Comment: 20 pages, 5 figures, submitted to AJ; final refereed versio
Effect of ELF e.m. fields on metalloprotein redox-active sites
The peculiarity of the distribution and geometry of metallic ions in enzymes
pushed us to set the hypothesis that metallic ions in active-site act like tiny
antennas able to pick up very feeble e.m. signals. Enzymatic activity of Cu2+,
Zn2+ Superoxide Dismutase (SOD1) and Fe2+ Xanthine Oxidase (XO) has been
studied, following in vitro generation and removal of free radicals. We
observed that Superoxide radicals generation by XO is increased by a weak field
having the Larmor frequency fL of Fe2+ while the SOD1 kinetics is sensibly
reduced by exposure to a weak field having the frequency fL of Cu2+ ion.Comment: 18 pages, 4 figure
Neutrino and antineutrino CCQE scattering in the SuperScaling Approximation from MiniBooNE to NOMAD energies
We compare the predictions of the SuperScaling model for charged current
quasielastic muonic neutrino and antineutrino scattering from C with
experimental data spanning an energy range up to 100 GeV. We discuss the
sensitivity of the results to different parametrizations of the nucleon vector
and axial-vector form factors. Finally, we show the differences between
electron and muon (anti-)neutrino cross sections relevant for the STORM
facility.Comment: 14 pages, 7 figures; v2: small corrections in the text and two added
references; version accepted for publication by Phys. Lett.
Connecting scaling with short-range correlations
We reexamine several issues related to the physics of scaling in electron
scattering from nuclei. A basic model is presented in which an assumed form for
the momentum distribution having both long- and short-range contributions is
incorporated in the single-particle Green function. From this one can obtain
saturation of nuclear matter for an NN interaction with medium-range attraction
and short-range repulsion, and can obtain the density-density polarization
propagator and hence the electromagnetic response and scaling function. For the
latter, the shape of the scaling function and how it approaches scaling as a
function of momentum transfer are both explored.Comment: 24 pages, 15 figures. A reference has been corrected and update
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