51 research outputs found
The Chemical Evolution of Starburst Nucleus Galaxies
The metallicities derived from spectroscopic observations of a sample of
Starburst Nucleus Galaxies (SBNGs) are compared to those of several other types
of galaxies (normal giant galaxies, Irregular and HII galaxies) drawn from the
literature. The SBNGs are deficient in metals with respect to normal galaxies
of same morphological type, suggesting that - SBNGs are galaxies still in the
process of formation.
Breaking the SBNGs into early-types (Sb and earlier) and late-types reveals
that the former seem to follow the same linear luminosity-metallicity relation
as the irregular and elliptical galaxies, whereas the latter and the giant
spirals show comparable (0.2 and 0.3 dex) excess abundances with respect to the
linear relation. This difference between the two types of SBNGs is consistent
with the predictions of the model of hierarchical formation of galaxies: the
early-type SBNGs are building their bulges by successive mergers of small
stellar and gaseous systems, while the late-type SBNGs are mostly accreting gas
to form a disk.Comment: accepted for publication in the ApJ Lette
Chemical evolution of starburst galaxies: How does star formation proceed?
We compute chemical evolution models to constrain the mode and the history of
star formation in starburst galaxies as a whole, i.e. over a large range of
mass and metallicity. To this end, we investigate the origin of the dispersion
observed in the evolution of both nitrogen-to-oxygen abundance ratio and galaxy
luminosity as a function of metallicity for a large sample of starburst
galaxies. We find that the variation of the star formation efficiency, in the
framework of continuous star formation models, produce a scatter equivalent to
what is observed in the N/O versus O/H diagram for low-mass HII galaxies only.
However, continous star formation models are unable to reproduce i) the scatter
observed for massive starburst and UV-selected galaxies in the N/O versus O/H
relation, and ii) the scatter in the luminosity versus O/H scaling relation
observed for the whole sample of starburst galaxies. The dispersion associated
with the distribution of N/O as a function of metallicity, for both low-mass
and massive galaxies, is well explained in the framework of bursting star
formation models. It is interpreted as a consequence of the time-delay between
the ejection of nitrogen and that of oxygen into the ISM. These models also
reproduce the spread observed in the luminosity-metallicity relation.
Metal-rich spiral galaxies differ from metal-poor ones by a higher star
formation efficiency and starburst frequency. Low-mass galaxies experienced a
few bursts of star formation whereas massive spiral galaxies experienced
numerous and extended powerful starbursts (abridged version).Comment: 9 pages, 4 figures. Accepted for publication in A&
BIFURCATION ANALYSIS VERSUS MAXIMUM FORCE CRITERIA IN FORMABILITY LIMIT ASSESSMENT OF STRETCHED METAL SHEETS
MASSIV: Mass Assembly Survey with SINFONI in VVDS. III. Evidence for positive metallicity gradients in z~1.2 star-forming galaxies
A key open issue for galaxy evolution and formation models is the
understanding of the different mechanisms of galaxy assembly at various cosmic
epochs. The aim of this study is to derive the global and spatially-resolved
metal content in high-redshift galaxies. Using VLT/SINFONI IFU spectroscopy of
a first sample of 50 galaxies at z~1.2 in the MASSIV survey, we are able to
measure the Ha and [NII]6584 emission lines. Using the N2 ratio as a proxy for
oxygen abundance in the interstellar medium, we measure the metallicity of the
sample galaxies. We develop a tool to extract spectra in annular regions of
these galaxies, leading to a spatially-resolved estimate of the oxygen
abundance in each galaxy. We derive a metallicity gradient for 26 galaxies in
our sample and discover a significant fraction of galaxies with a "positive"
gradient. Using a simple chemical evolution model, we derive infall rates of
pristine gas onto the disks. Seven galaxies display a positive gradient at a
high confidence level. Four out of these are interacting and one is a chain
galaxy. We suggest that interactions might be responsible for shallowing and
even inverting the abundance gradient. We also identify two interesting
correlations in our sample: a) galaxies with higher gas velocity dispersion
have shallower/positive gradients; and b) metal-poor galaxies tend to show a
positive gradient whereas metal-rich ones tend to show a negative one. This
last observation can be explained by the infall of metal-poor gas into the
center of the disks. We address the question of the origin of this infall under
the influence of gas flows triggered by interactions and/or cold gas accretion.Comment: 13 pages, 9 figures. Accepted for publication in A&
Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic properties
We performed a compilation of more than 1000 published spectra of HII regions
in spiral galaxies. The oxygen and nitrogen abundances in each HII region were
recomputed in a homogeneous way, using the P-method. The radial distributions
of oxygen and nitrogen abundances were derived. The correlations between oxygen
abundance and macroscopic properties are examined. There is a significant
difference between the L-Z relationship obtained here and that based on the
oxygen abundances determined through the R_23-calibrations. The oxygen
abundance of NGC 5457 recently determined using direct measurements of Te
(Kennicutt, Bresolin & Garnett 2003) agrees with the L-Z relationship derived
here, but is in conflict with the L-Z relationship derived with the R_23-based
oxygen abundances. The obtained L-Z relation for spirals is compared to that
for irregulars. Our sample of galaxies shows evidence that the slope of the
O/H-M_B relationship for spirals is slightly more shallow than that for
irregulars. The effective oxygen yields were estimated for spiral and irregular
galaxies. The effective oxygen yield increases with increasing luminosity from
M_B=-11 to M_B=-18 (or with increasing rotation velocity from Vrot=10 km/s to
Vrot=100 km/s) and then remains approximately constant. Irregular galaxies from
our sample have effective oxygen yields lowered by a factor of 3 at maximum,
i.e. irregular galaxies usually keep at least 1/3 of the oxygen they
manufactured during their evolution.Comment: Accepted for publication in Astronomy and Astrophysics (Figures 2-5,
Tables 2,6 and Appendix will only be published in the electronic version of
the Journal
Criteria for extensional necking instability in complex fluids and soft solids. Part II: Imposed tensile stress and force protocols
Criteria for extensional necking instability in complex fluids and soft solids. Part I: Imposed Hencky strain rate protocol
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