420 research outputs found
Hidden interaction in SBO galaxies
Galaxies, like plants, show a large variety of grafts: an individual of some type connects physically with a neighborhood of same or different type. The effects of these interactions between galaxies have a broad range of morphologies depending, among other quantities, on the distance of the closest approach between systems and the relative size of the two galaxies. A sketch of the possible situations is shown in tabular form. This botanical classification is just indicative, because the effects of interactions can be notable also at relatively large separations, when additional conditions are met, as for example low density of the interacting systems or the presence of intra-cluster gas. In spite of the large variety of encounters and effects, in the literature the same terms are often used to refer to different types of interactions. Analysis indicates that only few of the situations show evident signs of interaction. They appear to be most relevant when the size of the two galaxies is comparable. Bridges and tails, like the well known case of NGC 4038/39, the Antennae, are only observed for a very low percentage of all galaxies (approx. 0.38 percent, Arp and Madore 1977). In most cases of gravitational bond between two galaxies, the effects of interactions are not relevant or evident. For instance, the detection of stellar shells (Malin and Carter 1983), which have been attributed to the accretion of gas stripped from another galaxy or to the capture and disruption of a small stellar system (Quinn 1984), requires particular observing and reduction techniques. Besides these difficulties of detection, time plays an important role in erasing, within a massive galaxy, the effects of interactions with smaller objects. This can happen on a timescale shorter than the Hubble time, so the number of systems now showing signs of interaction suggests lower limits to the true frequency of interactions in the life-time of a stellar system
Surviving on Mars: test with LISA simulator
We present the biological results of some experiments performed in the Padua
simulators of planetary environments, named LISA, used to study the limit of
bacterial life on the planet Mars. The survival of Bacillus strains for some
hours in Martian environment is shortly discussed.Comment: To be published on Highlights of Astronomy, Volume 15 XXVIIth IAU
General Assembly, August 2009 Ian F Corbett, ed. 2 pages, 1 figur
Molecular gas and star formation in M81
We present IRAM 30m observations of the central 1.6 kpc of the spiral M81
galaxy. The molecular gas appears weak and with an unusual excitation physics.
We discuss a possible link between low CO emission and weak FUV surface
brightness.Comment: 2 pages, 2 figures, to appear in "Pathways through an eclectic
Universe", J. H. Knapen, T. J. Mahoney, and A. Vazdekis (Eds.), ASP Conf.
Ser., 200
Study of ISM tracers in galaxies
We collected data for two samples of normal and interacting galaxies for a
total of 2953 galaxies having fluxes in one or more of the following wavebands:
FIR, 21 cm line, CO(1-0) lines and soft X-ray. The large set of data obtained
allowed us to revisit some of the already known relations between the different
tracers of the interstellar medium (ISM), such as the link between the FIR flux
and the CO line emission, the relation between X-ray emission and the blue or
FIR luminosity. The relation lacking from observations for early-type galaxies
has been discussed and explained in detail in the frame of a suitable
theoretical model, obtained by coupling chemo-dynamical N-body simulations with
a dusty spectrophotometric code of population synthesis.Comment: 2 pages, o appear in the Proceedings of the Conf. "From Stars to
Galaxies: Building the Pieces to Build Up the Universe", Vallenari et al.
eds., ASP Conf. Serie
Catching Spiral - S0 transition in groups. Insights from SPH simulations with chemo-photometric implementation
We are investigating the co-evolution of galaxies within groups combining
multi-wavelength photometric and 2D kinematical observations. Here we focus on
S0s showing star formation in ring/arm-like structures. We use smooth particle
hydrodynamical simulations (SPH) with chemo-photometric implementation which
provide dynamical and morphological information together with the spectral
energy distribution (SED) at each evolutionary stage. As test cases, we
simulate the evolution of two such S0s: NGC 1533 and NGC 3626. The merging of
two halos with mass ratio 2:1, initially just composed of dark matter (DM) and
gas, well match their observed SEDs, their surface brightness profiles and
their overall kinematics. The residual star formation today "rejuvenating" the
ring/arm like structures in these S0s is then a mere consequence of a major
merger, i.e. this is a phase during the merger episode. The peculiar
kinematical features, e.g. gas-stars counter rotation in NGC 3626, depends on
the halos initial impact parameters. Furthermore, our simulations allow to
follow, in a fully consistent way, the transition of these S0s through the
green valley in the NUV-r vs. Mr colour magnitude diagram, which they cross in
about 3-5 Gyr, before reaching their current position in the red sequence. We
conclude that a viable mechanism driving the evolution of S0s in groups is of
gravitational origin.Comment: 30 pages, 6 figures; accepted for publication in Advances in Space
Research, Special Issue: Ultraviolet Astrophysic
Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud
With the aim of investigating galaxy evolution in nearby galaxy groups, we
analysed the spectral energy distribution of 24 galaxies, members of two groups
in the Leo cloud, USGC U268 and USGC U376. We estimated the ages and stellar
masses of the galaxies by fitting their total apparent magnitudes from
far-ultraviolet to near-infrared with population synthesis models. The
comparison of the results for a subsample of galaxies with smooth particle
hydrodynamic (SPH) simulations with chemo-photometric implementation, shows
that in most cases the estimated stellar masses obtained with the two different
approaches are in good agreement. The kinematical and dynamical analysis
indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is
likely in a more evolved phase towards virialization.Comment: 16 pages, 6 figures; accepted for publication in Advances in Space
Research, Special Issue: Ultraviolet Astrophysic
Are truncated stellar disks linked to the molecular gas density?
We know that the slope of the radial, stellar light distribution in galaxies
is well described by an exponential decline and this distribution is often
truncated at a break radius (). We don't have a clear understanding for
the origin of these outer truncations and several hypotheses have been proposed
to explain them. We want to test the various theories with direct observations
of the cold molecular gas for a few truncated galaxies in comparison with the
non-truncated ones. The answer to the existence of a possible link between
truncated stellar disks and the molecular gas density cannot be obtained from
CO maps in the literature, because so far there are no galaxies with a clear
truncation observed in CO at high resolution.Comment: 3 pages, 6 figures, to appear in Astrophysics and Space Science
(Apss), special issue of "Science with ALMA: a new era for Astrophysics"
conference, ed. Dr. Bachille
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