444 research outputs found
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
A Survey of Merger Remnants II: The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51 {\it
optically} selected, single-nuclei merger remnants. Spectroscopic data have
been obtained for a sub-sample of 38 mergers and combined with previously
obtained infrared photometry to test whether mergers exhibit the same
correlations as elliptical galaxies among parameters such as stellar luminosity
and distribution, central stellar velocity dispersion (), and
metallicity. Paramount to the study is to test whether mergers lie on the
Fundamental Plane. Measurements of have been made using the
Ca triplet absorption line at 8500 {\AA} for all 38 mergers in the sub-sample.
Additional measurements of were made for two of the mergers
in the sub-sample using the CO absorption line at 2.29 \micron. The results
indicate that mergers show a strong correlation among the parameters of the
Fundamental Plane but fail to show a strong correlation between
and metallicity (Mg). In contrast to earlier studies,
the of the mergers are consistent with objects which lie
somewhere between intermediate-mass and luminous giant elliptical galaxies.
However, the discrepancies with earlier studies appears to correlate with
whether the Ca triplet or CO absorption lines are used to derive
, with the latter almost always producing smaller values.
Finally, the photometric and kinematic data are used to demonstrate for the
first time that the central phase-space density of mergers are equivalent to
elliptical galaxies. This resolves a long-standing criticism of the merger
hypothesis.Comment: Accepted Astronomical Journal (to appear in January 2006
Alley coppice: an innovative land use system - options of system design with experimental evidence
Agroforestry and Short Rotation Coppice (SRC), for timber and bioenergy wood production, are recognized as economically viable and sustainable as separate cropping systems under ideal growing conditions. Little is known about agricultural and ecological interactions which might occur combining them in a tree-based intercropping system. This mixed approach, called alley coppice, is currently investigated in an European research Project (www.agrocop.com), and has important advantages: (i) a regular income guaranteed from the SRC component; (ii) light competition between species can often improve the stem form of timber trees; (iii) timber trees can be planted at the final spacing, avoiding expensive thinning; (iv) SRC component protects young timber trees from wind/storm damage; (v) alley coppice is expected to have positive impacts on biodiversity, and reducing soil erosion.
Three system designs are currently investigated: Simultaneous planting (SP); Lagged planting (LP) and Border planting (BP). In SP, timber and SRC components are planted in the same year; the key investigated factor is the distance between timber trees and the first SRC row, comparing 1, 2, 3 m in plantations in Ireland, Germany and Italy. A tree row width of three meters guaranteed satisfying growth rates of Sorbus and Pyrus timber trees in a mixture with 2-yr SRC poplar (Populus spp) in Italy, improving timber wood quality. LP, with planting SRC under adult timber trees, is studied in France and Ireland, according to timber tree age, species and inter-row spacings. In France, light and water competition had significant effects on poplar SRC growth and yield according to the distance from the walnut trees. BP involves planting timber trees along the borders of SRC blocks. Experimental plantations were established in Ireland and Germany, with the aim of avoiding asymmetric light competition that might hamper stem form of timber trees.
Guidelines for practitioners on alley coppice optimization will be provided at the end of the project
Constraints on the kinematics of the 44Ti ejecta of Cassiopeia A from INTEGRAL/SPI
The medium-lived 44Ti isotope is synthesised by explosive Si-burning in
core-collapse supernovae. It is extremely sensitive to the dynamics of the
explosion and therefore can be used to indirectly probe the explosion scenario.
The young supernova remnant Cassiopeia A is to date the only source of
gamma-ray lines from 44Ti decay. The emission flux has been measured by
CGRO/COMPTEL, BeppoSAX/PDS and INTEGRAL/IBIS. The high-resolution spectrometer
SPI on-board the INTEGRAL satellite can provide spectrometric information about
the emission. The line profiles reflect the kinematics of the 44Ti in
Cassiopeia A and can thus place constraints on its nucleosynthesis and
potentially on the associated explosion process. Using 4 years of data from
INTEGRAL/SPI, we have searched for the gamma-ray signatures from the decay of
the 44Ti isotope. The overwhelming instrumental background noise required an
accurate modelling and a solid assessment of the systematic errors in the
analysis. Due to the strong variability of the instrumental background noise,
it has not been possible to extract the two lines at 67.9 and 78.4keV.
Regarding the high-energy line at 1157.0keV, no significant signal is seen in
the 1140-1170keV band, thereby suggesting that the line signal from Cassiopeia
A is broadened by the Doppler effect. From our spectrum, we derive a ~ 500km/s
lower limit at 2sigma on the expansion velocity of the 44Ti ejecta. Our result
does not allow us to constrain the location of 44Ti since the velocities
involved throughout the remnant, derived from optical and X-ray studies, are
all far above our lower limit.Comment: 7 pages, 8 figures, published in A&
Laser frequency stabilization using folded cavity and mirror reflectivity tuning
International audienceA new method of laser frequency stabilization using polarization property of an optical cavity is proposed. In a standard FabryâPerot cavity, the coating layers thickness of cavity mirrors is calculated to obtain the same phase shift for sand p-wave but a slight detuning from the nominal thickness can produce sand p-wave phase detuning. As a result, each wave accumulates a different round-trip phase shift and resonates at a different frequency. Using this polarization property, an error signal is generated by a simple setup consisting of a quarter wave-plate rotated at 45°, a polarizing beam splitter and two photodiodes. This method exhibits similar error signal as the PoundâDreverâHall technique but without need for any frequency modulation. Lock theory and experimental results are presented in this paper.
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
Nearby early-type galaxies with ionized gas VI. The Spitzer-IRS view
We present low resolution Spitzer-IRS spectra of 40 ETGs, selected from a
sample of 65 ETGs showing emission lines in their optical spectra. We
homogeneously extract the mid-infrared (MIR) spectra, and after the proper
subtraction of a "passive" ETG template, we derive the intensity of the ionic
and molecular lines and of the polycyclic aromatic hydrocarbon emission
features. We use MIR diagnostic diagrams to investigate the powering mechanisms
of the ionized gas. The mid-infrared spectra of early-type galaxies show a
variety of spectral characteristics. We empirically sub-divide the sample into
five classes of spectra with common characteristics. Class-0, accounting for
20% of the sample, are purely passive ETGs with neither emission lines nor PAH
features. Class-1 show emission lines but no PAH features, and account for
17.5% of the sample. Class-2, in which 50% of the ETGs are found, as well as
having emission lines, show PAH features with unusual ratios, e.g. 7.7
{\mu}m/11.3 {\mu}m \leq 2.3. Class-3 objects have emission lines and PAH
features with ratios typical of star-forming galaxies. 7.5% of objects fall in
this class, likely to be objects in a starburst/post-starburst regime. Class-4,
containing only 5% of the ETGs, is dominated by a hot dust continuum. The
diagnostic diagram [Ne III]15.55{\mu}m/[Ne II]12.8{\mu}m vs. [S
III]33.48{\mu}m/[Si II]34.82{\mu}m, is used to investigate the different
mechanisms ionizing the gas. If we exclude NGC 3258 where a starburst seems
present, most of our ETGs contain gas ionized via either AGN-like or shock
phenomena, or both. Most of the spectra in the present sample are classified as
LINERs in the optical window. The proposed MIR spectral classes show
unambiguously the manifold of the physical processes and ionization mechanisms,
from star formation, low level AGN activity, to shocks, present in LINER
nuclei.Comment: Accepted for publication in Astronomy and Astrophysic
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