18 research outputs found
Geometrical tests of cosmological models. III. The cosmology-evolution diagram at z=1
The rotational velocity of distant galaxies, when interpreted as a size
(luminosity) indicator, may be used as a tool to select high redshift standard
rods (candles) and probe world models and galaxy evolution via the classical
angular diameter-redshift or Hubble diagram tests. We implement the proposed
testing strategy using a sample of 30 rotators spanning the redshift range
0.2<z<1 with high resolution spectra and images obtained by the VIMOS/VLT Deep
Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs).
We show that by applying at the same time the angular diameter-redshift and
Hubble diagrams to the same sample of objects (i.e. velocity selected galactic
discs) one can derive a characteristic chart, the cosmology-evolution diagram,
mapping the relation between global cosmological parameters and local
structural parameters of discs such as size and luminosity. This chart allows
to put constraints on cosmological parameters when general prior information
about discs evolution is available. In particular, by assuming that equally
rotating large discs cannot be less luminous at z=1 than at present (M(z=1) <
M(0)), we find that a flat matter dominated cosmology (Omega_m=1) is excluded
at a confidence level of 2sigma and an open cosmology with low mass density
(Omega_m = 0.3) and no dark energy contribution is excluded at a confidence
level greater than 1 sigma. Inversely, by assuming prior knowledge about the
cosmological model, the cosmology-evolution diagram can be used to gain useful
insights about the redshift evolution of the structural parameters of baryonic
discs hosted in dark matter halos of nearly equal masses.Comment: 14 pages and 11 figures. A&A in pres
Interpreting the Evolution of the Size - Luminosity Relation for Disk Galaxies from Redshift 1 to the Present
A sample of very high resolution cosmological disk galaxy simulations is used
to investigate the evolution of galaxy disk sizes back to redshift 1 within the
Lambda CDM cosmology. Artificial images in the rest frame B band are generated,
allowing for a measurement of disk scale lengths using surface brightness
profiles as observations would, and avoiding any assumption that light must
follow mass as previous models have assumed. We demonstrate that these
simulated disks are an excellent match to the observed magnitude - size
relation for both local disks, and for disks at z=1 in the magnitude/mass range
of overlap. We disentangle the evolution seen in the population as a whole from
the evolution of individual disk galaxies. In agreement with observations, our
simulated disks undergo roughly 1.5 magnitudes/arcsec^2 of surface brightness
dimming since z=1. We find evidence that evolution in the magnitude - size
plane varies by mass, such that galaxies with M* > 10^9 M_sun undergo more
evolution in size than luminosity, while dwarf galaxies tend to evolve
potentially more in luminosity. The disks grow in such a way as to stay on
roughly the same stellar mass - size relation with time. Finally, due to an
evolving stellar mass - SFR relation, a galaxy at a given stellar mass (or
size) at z=1 will reside in a more massive halo and have a higher SFR, and thus
a higher luminosity, than a counterpart of the same stellar mass at z=0.Comment: Version resubmitted to ApJ, after referee's comment
The SINS survey: modeling the dynamics of z~2 galaxies and the high-z Tully-Fisher relation
We present the modeling of SINFONI integral field dynamics of 18 star forming
galaxies at z ~ 2 from Halpha line emission. The galaxies are selected from the
larger sample of the SINS survey, based on the prominence of ordered rotational
motions with respect to more complex merger induced dynamics. The quality of
the data allows us to carefully select systems with kinematics dominated by
rotation, and to model the gas dynamics across the whole galaxy using suitable
exponential disk models. We obtain a good correlation between the dynamical
mass and the stellar mass, finding that large gas fractions Mgas~M*) are
required to explain the difference between the two quantities. We use the
derived stellar mass and maximum rotational velocity Vmax from the modeling to
construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2.
The relation obtained shows a slope similar to what is observed at lower
redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2
there is an offset in log(M*) for a given rotational velocity of 0.41+-0.11
with respect to the local Universe. This result is consistent with the
predictions of the latest N-body/hydrodynamical simulations of disk formation
and evolution, which invoke gas accretion onto the forming disk in filaments
and cooling flows. This scenario is in agreement with other dynamical evidence
from SINS, where gas accretion from the halo is required to reproduce the
observed properties of a large fraction of the z ~ 2 galaxies.Comment: 10 pages, 6 figures, submitted to Ap
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Chemical Mapping of Ancient Artifacts and Fossils with X-Ray Spectroscopy
International audienc
The GALAH survey: scientific motivation
The GALAH survey is a large high-resolution spectroscopic survey using the
newly commissioned HERMES spectrograph on the Anglo-Australian Telescope. The
HERMES spectrograph provides high-resolution (R ~28,000) spectra in four
passbands for 392 stars simultaneously over a 2 degree field of view. The goal
of the survey is to unravel the formation and evolutionary history of the Milky
Way, using fossil remnants of ancient star formation events which have been
disrupted and are now dispersed throughout the Galaxy. Chemical tagging seeks
to identify such dispersed remnants solely from their common and unique
chemical signatures; these groups are unidentifiable from their spatial,
photometric or kinematic properties. To carry out chemical tagging, the GALAH
survey will acquire spectra for a million stars down to V~14. The HERMES
spectra of FGK stars contain absorption lines from 29 elements including light
proton-capture elements, alpha-elements, odd-Z elements, iron-peak elements and
n-capture elements from the light and heavy s-process and the r-process. This
paper describes the motivation and planned execution of the GALAH survey, and
presents some results on the first-light performance of HERMES.Comment: 16 pages, 7 figure