48,655 research outputs found
A Model for Dark Matter Halos
A halo model is presented which possesses a constant phase space density (Q)
core followed by a radial CDM-like power law decrease in Q. The motivation for
the core is the allowance for a possible primordial phase space density limit
such as the Tremaine-Gunn upper bound. The space density profile derived from
this model has a constant density core and falls off rapidly beyond. The new
model is shown to improve the fits to the observations of LSB galaxy rotation
curves, naturally provides a model which has been shown to result in a
lengthened dynamical friction time scale for the Fornax dwarf spheroidal galaxy
and predicts a flattening of the density profile within the Einstein radius of
galaxy clusters. A constant gas entropy floor is predicted whose adiabatic
constant provides a lower limit in accord with observed galaxy cluster values.
While `observable-sized' cores are not seen in standard cold dark matter (CDM)
simulations, phase space considerations suggest that they could appear in warm
dark matter (WDM) cosmological simulations and in certain hierarchically
consistent SuperWIMP scenarios.Comment: 14 pages, 3 figures, accepted for publication in Ap
SAOLIM, a prototype of a low cost System for Adaptive Optics with Lucky Imaging
A prototype of a low cost Adaptive Optics (AO) system has been developed at
the Instituto de Astrofisica de Andalucia (CSIC) and tested at the 2.2m
telescope of the Calar Alto observatory. We present here the status of the
project, which includes the image stabilization system and compensation of high
order wavefront aberrations with a membrane deformable mirror. The image
stabilization system consists of magnet driven tip-tilt mirror. The higher
order compensation system comprises of a Shack-Hartmann sensor, a membrane
deformable mirror with 39 actuators and the control computer that allows
operations up to 420Hz in closed loop mode. We have successfully closed the
high order AO loop on natural guide stars. An improvement of 4 times in terms
of FWHM was achieved. The description and the results obtained on the sky are
presented in this paper.Comment: Accepted for publishing in PASP, 11 pages, 14 figures, 6 table
Cluster of galaxies around seven radio-loud QSOs at 1<z<1.6: K-band images
We have conducted a NIR study of the environments of seven radio-loud quasars
at redshifts 1<z<1.6. In present paper we describe deep band images
obtained for the fields of ~6X6 arcmin around the quasars with 3
limiting magnitudes of K~20.5. These fields were previously studied using deep
B and R band images (Sanchez & Gonzalez-Serrano 1999). Using together optical
and NIR data, it has been found a significant excess of galaxies which
optical-NIR colours, luminosity, spatial scale, and number of galaxies are
compatible with clusters at the redshift of the quasar.
We have selected a sample of cluster candidates analyzing the R-K vs. K
diagram. A ~25% of the candidates present red optical-NIR colours and an
ultraviolet excess. This population has been also found in clusters around
quasars at the same redshifts (Tanaka et al. 2000; Haines et al. 2001). These
galaxies seem to follow a mixed evolution: a main passive evolution plus late
starformation processes. The quasars do not inhabit the core of the clusters,
being found in the outer regions. This result agrees with the hypothesis that
the origin/feeding mechanism of the nuclear activity were merging processes.
The quasars inhabit the region were a collision is most probably to produce a
merger.Comment: 15 pages. A&A, accepted for publishin
Light-related variation in sapling architecture of three shade-tolerant tree species of the Mexican rain forest
The crown architecture of three shade-tolerant tree species (two subcanopy and one mid-canopy) was analyzed in relation to the light regime of the forest understorey. The aim was to examine to which extent shade-tolerant species variate in their crown architecture. Tree saplings (265) between 50 and 300 cm height, and distributed from understorey to variously-sized canopy gaps, were measured for 13 architectural traits in the lowland rain forest of Los Tuxtlas, Mexico. The analysis showed that the three species changed their architecture as light increased but in a different way. No species conformed to the typical wide-crown type expected for shade-tolerant species, and in contrast they presented some traits of light demanding species. The two sub-canopy species tended to adopt a crown form between a narrow- and wide-crown type, and the mid-canopy species showed more traits of a narrow-crown type. The horizontal crown area appeared as the more related trait to the light and sapling height. It is concluded that despite being shade-tolerant, the Studied species make use of better-lit environments in the forest understorey. The crown architecture of shade-tolerant species is not Lis rigid Lis originally conceived
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