418 research outputs found
Breaking the Disk/Halo Degeneracy with Gravitational Lensing
The degeneracy between the disk and the dark matter contribution to galaxy
rotation curves remains an important uncertainty in our understanding of disk
galaxies. Here we discuss a new method for breaking this degeneracy using
gravitational lensing by spiral galaxies, and apply this method to the spiral
lens B1600+434 as an example. The combined image and lens photometry
constraints allow models for B1600+434 with either a nearly singular dark
matter halo, or a halo with a sizable core. A maximum disk model is ruled out
with high confidence. Further information, such as the circular velocity of
this galaxy, will help break the degeneracies. Future studies of spiral galaxy
lenses will be able to determine the relative contribution of disk, bulge, and
halo to the mass in the inner parts of galaxies.Comment: Replaced with minor revisions, a typo fixed, and reference added; 21
pages, 8 figures, ApJ accepte
The power spectrum from the angular distribution of galaxies in the CFHTLS-Wide fields at redshift ~0.7
We measure the real-space galaxy power spectrum on large scales at redshifts
0.5 to 1.2 using optical colour-selected samples from the CFHT Legacy Survey.
With the redshift distributions measured with a preliminary ~14000
spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey
(VIPERS), we deproject the angular distribution and directly estimate the
three-dimensional power spectrum. We use a maximum likelihood estimator that is
optimal for a Gaussian random field giving well-defined window functions and
error estimates. This measurement presents an initial look at the large-scale
structure field probed by the VIPERS survey. We measure the galaxy bias of the
VIPERS-like sample to be b_g=1.38 +- 0.05 (sigma_8=0.8) on scales k<0.2h/mpc
averaged over 0.5<z<1.2. We further investigate three photometric redshift
slices, and marginalising over the bias factors while keeping other LCDM
parameters fixed, we find the matter density Omega_m=0.30+-0.06.Comment: Minor changes to match journal versio
NICMOS images of JVAS/CLASS gravitational lens systems
We present Hubble Space Telescope (HST) infrared images of four gravitational
lens systems from the JVAS/CLASS gravitational lens survey and compare the new
infrared HST pictures with previously published WFPC2 HST optical images and
radio maps. Apart from the wealth of information that we get from the flux
ratios and accurate positions and separations of the components of the lens
systems that we can use as inputs for better constraints on the lens models we
are able to discriminate between reddening and optical/radio microlensing as
the possible cause of differences observed in the flux ratios of the components
across the three wavelength bands. Substantial reddening has been known to be
present in the lens system B1600+434 and has been further confirmed by the
present infrared data. In the two systems B0712+472 and B1030+074 microlensing
has been pinpointed down as the main cause of the flux ratio discrepancy both
in the optical/infrared and in the radio, the radio possibly caused by the
substructure revealed in the lensing galaxies. In B0218+357 however the results
are still not conclusive. If we are actually seeing the two "true" components
of the lens system then the flux ratio differences are attributed to a
combination of microlensing and reddening or alternatively due to some
variability in at least one of the images. Otherwise the second "true"
component of B0218+357 maybe completely absorbed by a molecular cloud and the
anomalous flux density ratios and large difference in separation between the
optical/infrared and radio that we see can be explained by emission from either
a foreground object or from part of the lensing galaxy.Comment: 10 pages, 4 figures (original higher resolution figures can be
obtained at the e-mail above), to appear in MNRAS (accepted
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Nature: a new paradigm for well-being and ergonomics
Nature is presented as a new paradigm for ergonomics. As a discipline concerned with well-being, the importance of natural environments for wellness should be part of ergonomics knowledge and practice. This position is supported by providing a concise summary of the evidence of the value of the natural environment to well-being. Further, an emerging body of research has found relationships between well-being and a connection to nature, a concept that reveals the integrative character of human experience which can inform wider practice and epistemology in ergonomics. Practitioners are encouraged to bring nature into the workplace, so that ergonomics keeps pace with the move to nature-based solutions, but also as a necessity in the current ecological and social context. Practitioner Summary: Nature-based solutions are coming to the fore to address societal challenges such as well-being. As ergonomics is concerned with well-being, there is a need for a paradigm shift in the discipline. This position is supported by providing a concise summary of the evidence of the value of the natural environment to well-being
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
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