2,145 research outputs found
Molecular content of a type-Ia SN host galaxy at z=0.6
We study the properties and the molecular content of the host of a type-Ia
supernova (SN1997ey). This z=0.575 host is the brightest submillimetre source
of the sample of type-Ia supernova hosts observed at 450um and 850um by Farrah
et al.. Observations were performed at IRAM-30m to search for CO(2-1) and
CO(3-2) lines in good weather conditions but no signal was detected. The star
formation rate cannot exceed 50 M_sol/yr. These negative results are confronted
with an optical analysis of a Keck spectrum and other data archives. We reach
the conclusion that this galaxy is a late-type system (0.7 L^B_*), with a small
residual star-formation activity (0.2 M_sol/yr) detected in the optical. No
source of heating (AGN or starburst) is found to explain the
submillimetre-continuum flux and the non-CO detection excludes the presence of
a large amount of cold gas. We thus suggest that either the star formation
activity is hidden in the nucleus (with A_V ~ 4) or this galaxy is passive or
anemic and this flux might be associated with a background galaxy.Comment: 8 pages, 7 figures, accepted for publication in MNRA
CO investigation of z=0.4-1.5 galaxies
We report on the results of an IRAM-30m search for CO emission lines in three
galaxies at intermediate redshifts. The idea was to investigate the molecular
content of galaxies bright in the infrared at z=0.4-1.5, a redshift desert for
molecular line studies, poorly investigated as of yet. We integrated 8-10h per
source and did not succeed in detecting any of the sources. From our upper
limits, we are able to constrain the molecular gas content in these systems to
less than 4 to 8 x 10^9 Mo, assuming a CO-to-H_2 conversion factor (\alpha=0.8
Mo/(K km s^-1 pc^2)). We stress the current difficulty of selecting sources
with a detectable molecular content, a problem that will be faced by the ALMA
First Science projects.Comment: 6 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysic
Detection of CO in the inner part of M31's bulge
We report the first detection of CO in M31's bulge. The 12CO (1-0) and (2-1)
lines are both detected in the dust complex D395A/393/384, at 1.3" (~0.35 kpc)
from the centre. From these data and from visual extinction data, we derive a
CO-luminosity to reddening ratio (and a CO-luminosity to H_2 column density
ratio) quite similar to that observed in the local Galactic clouds. The (2-1)
to (1-0) line intensity ratio points to a CO rotational temperature and a gas
kinetic temperature > 10 K. The molecular mass of the complex, inside a 25'
(100 pc) region, is 1.5 10^4 Mo.Comment: 5 pages including 4 figures (2 in colour
Star formation efficiency in galaxy interactions and mergers: a statistical study
We investigate the enhancement of star formation efficiency in galaxy
interactions and mergers, by numerical simulations of several hundred galaxy
collisions. All morphological types along the Hubble sequence are considered in
the initial conditions of the two colliding galaxies, with varying
bulge-to-disk ratios and gas mass fractions. Different types of orbits are
simulated, direct and retrograde, according to the initial relative energy and
impact parameter, and the resulting star formation history is compared to that
occuring in the two galaxies when they are isolated. Our principal results are:
(1) retrograde encounters have a larger star formation efficiency (SFE) than
direct encounters; (2) the amount of gas available in the galaxy is not the
main parameter governing the SFE in the burst phase; (3) there is an
anticorrelation between the amplitude of the star forming burst and the tidal
forces exerted per unit of time, which is due to the large amount of gas
dragged outside the galaxy by tidal tails in strong interactions; (4) globally,
the Kennicutt-Schmidt law is retrieved statistically for isolated galaxies,
interacting pairs and mergers; (5) the enhanced star formation is essentially
occurring in nuclear starbursts, triggered by inward gas flows driven by
non-axisymmetries in the galaxy disks. Direct encounters develop more
pronounced asymmetries than retrograde ones. Based on these statistical
results, we derive general laws for the enhancement of star formation in galaxy
interactions and mergers, as a function of the main parameters of the
encounter.Comment: 22 pages, 37 figures, 4 tables. Accepted on Astronomy & Astrophysic
The Data Processing Pipeline for the Herschel-HIFI Instrument
The HIFI data processing pipeline was developed to systematically process
diagnostic, calibration and astronomical observations taken with the HIFI
science instrumentas part of the Herschel mission. The HIFI pipeline processed
data from all HIFI observing modes within the Herschel automated processing
environment, as well as, within an interactive environment. A common software
framework was developed to best support the use cases required by the
instrument teams and by the general astronomers. The HIFI pipeline was built on
top of that and was designed with a high degree of modularity. This modular
design provided the necessary flexibility and extensibility to deal with the
complexity of batch-processing eighteen different observing modes, to support
the astronomers in the interactive analysis and to cope with adjustments
necessary to improve the pipeline and the quality of the end-products. This
approach to the software development and data processing effort was arrived at
by coalescing the lessons learned from similar research based projects with the
understanding that a degree of foresight was required given the overall length
of the project. In this article, both the successes and challenges of the HIFI
software development process are presented. To support future similar projects
and retain experience gained lessons learned are extracted.Comment: 18 pages, 5 figure
Etude du comportement mécanique d'un liner de titane
National audienceIl s'agit dans ce travail d'étudier le comportement mécanique d'un liner constitué de titane T35, fourni sous la forme de feuillard de 300 μm d'épaisseur. Ce travail porte notamment sur la caractérisation du métal de base mais aussi sur celui des cordons de soudure.. Pour le matériau de base, les observations microstructurales ont révélé des grains équiaxes avec une texture classique de tôle laminée pour les matériaux hexagonaux. Les soudures montrent une microstructure moins régulière et une texture plus isotrope. D'un point de vue comportement mécanique, nous avons pu identifier au moyen d'essais de traction un comportement élastoviscoplastique anisotrope des tôles. Ces résultats expérimentaux ont permis l'identification de 3 modèles issus de la littérature, (Mises, Hill et Bron-Besson) donnant lieu à des comparaisons de simulation. Enfin une analyse tomographique réalisée à l'ESRF sur une éprouvette fissurée a révélée la présence de peu de cavités à proximité de la fissure
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