24,870 research outputs found
Transthyretin familial amyloid polyneuropathy impact on health-related quality of life
info:eu-repo/semantics/publishedVersio
Physical parameters in the hot spots and jets of Compact Symmetric Objects
We present a model to determine the physical parameters of jets and hot spots
of a sample of CSOs under very basic assumptions like synchrotron emission and
minimum energy conditions. Based on this model we propose a simple evolutionary
scenario for these sources assuming that they evolve in ram pressure
equilibrium with the external medium and constant jet power. The parameters of
our model are constrained from fits of observational data (radio luminosity,
hot spot radius and hot spot advance speed) versus projected linear size. From
these plots we conclude that CSOs evolve self-similarly and that their radio
luminosity increases with linear size along the first kiloparsec. Assuming that
the jets feeding CSOs are relativistic from both kinematical and
thermodynamical points of view, we use the values of the pressure and particle
number density within the hot spots to estimate the fluxes of momentum
(thrust), energy, and particles of these relativistic jets. The mean jet power
obtained in this way is within an order of magnitude that inferred for FRII
sources, which is consistent with CSOs being the possible precursors of large
doubles. The inferred flux of particles corresponds to, for a barionic jet,
about a 10% of the mass accreted by a black hole of at
the Eddington limit, pointing towards a very efficient conversion of accretion
flow into ejection, or to a leptonic composition of jets.Comment: 11 pages, 2 figures. Accepted for publication in Astrophysical
Journa
Dating COINS: Kinematic Ages for Compact Symmetric Objects
We present multi-epoch VLBA observations of Compact Symmetric Objects (CSOs)
from the COINS sample (CSOs Observed In the Northern Sky). These observations
allow us to make estimates of, or place limits on, the kinematic ages for those
sources with well-identified hot spots. This study significantly increases the
number of CSOs with well-determined ages or limits. The age distribution is
found to be sharply peaked under 500 years, suggesting that many CSOs die
young, or are episodic in nature, and very few survive to evolve into FR II
sources like Cygnus A. Jet components are found to have higher velocities than
hot spots which is consistent with their movement down cleared channels. We
also report on the first detections of significant polarization in two CSOs,
J0000+4054 (2.1%) and J1826+1831 (8.8%). In both cases the polarized emission
is found in jet components on the stronger side of the center of activity.Comment: 34 pages including 7 figures, Accepted to ApJ on Dec 7, 200
A Tolman Surface Brightness Test for Universal Expansion, and the Evolution of Elliptical Galaxies in Distant Clusters
We use the intercept of the elliptical galaxy radius--surface brightness (SB)
relation at a fixed metric radius as the standard condition for the Tolman SB
test of the universal expansion. We use surface photometry in the optical and
near-IR of elliptical galaxies in Abell~2390 () and Abell~851
(), and compare them to the Coma cluster at . The
photometric data for each cluster are well-described by the Kormendy relation
, where in the optical and in the
near-IR. The scatter about this near-IR relation is only in
at the highest redshift, which is much smaller than at low redshifts,
suggesting a remarkable homogeneity of the cluster elliptical population at
. We use the intercept of these fixed-slope correlations at ~kpc (assuming ~km~s~Mpc, , and
, where the results are only weakly dependent on the cosmology) to
construct the Tolman SB test for these three clusters. The data are fully
consistent with universal expansion if we assume simple models of passive
evolution for elliptical galaxies, but are inconsistent with a non-expanding
geometry (the tired light cosmology) at the confidence level at
. These results suggest luminosity evolution in the restframe -band
of ~mag from to the present, and are consistent with
the ellipticals having formed at high redshift. The SB intercept in elliptical
galaxy correlations is thus a powerful tool for investigating models of their
evolution for significant lookback times.Comment: to appear in The Astrophysical Journal (Letters); 13 pages, including
3 Postscript figures and 1 table; uuencoded, compressed format; the paper is
also available in various formats from
http://astro.caltech.edu/~map/map.bibliography.refereed.htm
- …