533 research outputs found
Agroforestry at all latitudes ? Unexpected results about best designs to allow more light to the crops at various latitudes
info:eu-repo/semantics/publishedVersio
CO observations of southern mergers
There are good reasons to believe that the formation of some elliptical galaxies result from the merging of two disk galaxies, as Toomre and Toomre first suggested (1972, Ap. J. 178, 623). Such a process strongly enhances the star-formation activity of the system, thus consuming its molecular gas. This might account for the low cold-gas content of elliptical galaxies compared to that of spirals. Researchers present here CO(1-0) and CO(2-1) observations of a sequence of three objects, NGC 1614, NGC 3256, and NGC 7252, that present characteristic features of merger remnants: single body and extended tidal tails. NGC 3256 and 7252 even exhibit the r(exp 1/4) radial light distribution that is the signature of elliptical galaxies, which indicates that their stellar bodies are in late stages of relaxation. Both NGC 1614 and NGC 3256 undergo extended bursts of star formation revealed by their large far-infrared luminosities, and by the presence in the near-infrared spectrum of the 3.28 microns feature (Morwood: 1986, A. A. 166, 4) attributed to polycyclic aromatic hydrocarbons. On the other hand, NGC 7252 has a milder activity of star formation, as suggested by a lower infrared luminosity, and thus seems to have gone past the starburst phase. The CO data were collected with the Swedish-ESO 15 m Submillimeter Telescope (SEST) (beamsize = 43 seconds at 115 GHz, 23 seconds at 230 GHz). For NGC 7252, researchers have only observed the central position in CO-12(1-0). The spectrum is displayed together with an HI spectrum obtained with the Nancay radiotelescope. Researchers mapped NGC 1614 and NGC 3256 in CO-12(1-0) and CO-12(2-1), and also observed the nucleus of NGC 3256 in CO-13(1-0). The various CO spectra obtained towards the nuclei of both galaxies are presented. Characteristics of the galaxies are gathered, with luminosities and masses in solar units and temperatures in Kelvins
Simulations of shell galaxies with GADGET-2: Multi-generation shell systems
As the missing complement to existing studies of shell galaxies, we carried
out a set of self-consistent N-body simulations of a minor merger forming a
stellar shell system within a giant elliptical galaxy. We discuss the effect of
a phenomenon possibly associated with the galaxy merger simulations --- a
presence of multiple generations of shells.Comment: 2 pages, 1 figure, to appear in the Proceedings of JENAM 2010,
Symposium 2: "Environment and the formation of galaxies: 30 years later
Two tails in NGC 3656, and the major merger origin of shell and minor axis dust lane ellipticals
I report on the discovery of two faint (~ 26.8 Rmag/arcsec^2) tidal tails
around the shell elliptical NGC 3656 (Arp 155). This galaxy had previously been
interpreted as a case of accretion, or minor merger. The two tidal tails are
inconsistent with a minor merger, and point instead to a disk-disk major merger
origin. NGC 3656 extends Toomre's merger sequence toward normal elliptical
galaxies, and hints at a major merger origin for shells and minor-axis dust
lanes. A dwarf galaxy lies at the tip of one of the tidal tails. A prominent
shell, which shows sharp azymuthal color discontinuities, belongs to a rotating
dynamical component of young stars which includes the inner dust lane.Comment: 9 pages, 2 plates, 1 figure, uses aaspp.sty, accepted for publication
in The Astrophysical Journal Letters. Files also available by anonymous ftp
at ftp.iac.es, directory ./pub/balcell
Aspects techniques des plantations d'arbres à bois en terres agricoles des plaines méditerranéennes
International audienc
High intensity X/ γ photon beams for nuclear physics and photonics
In this manuscript we review the challenges of Compton back-scattering sources in advancing photon beam performances in the1−20MeVenergy range, underlining the design criteria bringing tomaximum spectral luminosity and briefly describing the main achieve-ments in conceiving and developing new devices (multi-bunch RF cav-ities and Laser recirculators) for the case of ELI-NP Gamma BeamSystem (ELI-NP-GBS)
Evidence for Three Subpopulations of Globular Clusters in the Early-Type Post-Starburst Shell Galaxy AM 0139-655
We present deep HST ACS images of the post-starburt shell galaxy AM 0139-655.
We find evidence for the presence of three distinct globular cluster
subpopulations associated with this galaxy: a centrally concentrated young
population (~ 0.4 Gyr), an intermediate age population (~ 1 Gyr) and an old,
metal-poor population similar to that seen around normal galaxies. The g-I
color distribution of the clusters is bimodal with peaks at 0.85 and 1.35. The
redder peak at g-I=1.35 is consistent with the predicted color for an old
metal-poor population. The clusters associated with the peak at g-I=0.85 are
centrally concentrated and interpreted as a younger and more metal-rich
population. We suggest that these clusters have an age of ~ 0.4 Gyr and solar
metallicity based on a comparison with population synthesis models. The
luminosity function of these "blue" clusters is well represented by a power
law. Interestingly, the brightest shell associated with the galaxy harbors some
of the youngest clusters observed. This seems to indicate that the same merger
event was responsible for the formation of both the shells and the young
clusters. The red part of the color distribution contains several very bright
clusters, which are not expected for an old, metal-poor population.
Furthermore, the luminosity function of the "red" GCs cannot be fit well by
either a single gaussian or a single power law. A composite (gaussian + power
law) fit to the LF of the red clusters yields both a low rms and very plausible
properties for an old population plus an intermediate-age population of GCs.
Hence, we suggest that the red clusters in AM 0139-655 consist of two distinct
GC subpopulations, one being an old, metal-poor population as seen in normal
galaxies and one having formed during a recent dissipative galaxy merger.Comment: 35 pages, 12 figures, accepted for publication in A
How important is adapting regional climatic projections to the local environment? A procedure for microclimatic corrections makes the difference for crop growth in a virtual experiment.
Are Red Tidal Features Unequivocal Signatures of Major Dry Mergers?
We use a cosmological numerical simulation to study the tidal features
produced by a minor merger with an elliptical galaxy. We find that the
simulated tidal features are quantitatively similar to the red tidal features,
i.e., dry tidal features, recently found in deep images of elliptical galaxies
at intermediate redshifts. The minor merger in our simulation does not trigger
star formation due to active galactic nuclei heating. Therefore, both the tidal
features and the host galaxy are red, i.e. a dry minor merger. The stellar mass
of the infalling satellite galaxy is about 10^10 Msun, and the tidal debris
reach the surface brightness of mu_R~27 mag arcsec^-2. Thus, we conclude that
tidal debris from minor mergers can explain the observed dry tidal features in
ellipticals at intermediate redshifts, although other mechanisms (such as major
dry mergers) may also be important.Comment: 7 pages, 7 figures, accepted for publication in Ap
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