1,770 research outputs found
Hall effect in the normal state of high Tc cuprates
We propose a model for explaining the dependence in temperature of the Hall
effect of high Tc cuprates in the normal state in various materials. They all
show common features: a decrease of the Hall coefficient RH with temperature
and a universal law, when plotting RH(T)/RH(T0) versus T/T0, where T0 is
defined from experimental results. This behaviour is explained by using the
well known electronic band structure of the CuO2 plane, showing saddle points
at the energies ES in the directions (0,+/-pi) and (+/-pi,0). We remark that in
a magnetic field, for energies E>ES the carrier orbits are hole-like and for
E<ES they are electron-like, giving opposite contributions to RH. We are abble
to fit the experimental results for a wide range of hole doping, and to fit the
universal curve. For us kb*T0 is simply EF-ES, where EF is the Fermi level
varying with the doping.Comment: 7 pages, 11 figure
On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies
We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line
emission in five bright star-forming galaxies at 1.66<z<1.91 that have been
gravitationally lensed by foreground galaxy clusters. All five galaxies show
prominent Mg II emission and absorption in a P Cygni profile. We find no
correlation between the equivalent widths of Mg II and Lyman alpha emission.
The Mg II emission has a broader range of velocities than do the nebular
emission line profiles; the Mg II emission is redshifted with respect to
systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.
The reddest components of Mg II and Lyman alpha emission have tails to 500-600
km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman
alpha equivalent widths, the differing velocity profiles, and the high ratios
of Mg II to nebular line fluxes together suggest that the bulk of Mg II
emission does not ultimately arise as nebular line emission, but may instead be
reprocessed stellar continuum emission.Comment: The Astrophysical Journal, in press. 6 pages, 2 figure
The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra
We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies
Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises
medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright
gravitationally lensed galaxies at redshifts of 1.68z3.6, obtained with
the MagE spectrograph on the Magellan telescopes. The spectra cover the
observed-frame wavelength range \AA ; the average
spectral resolving power is R=3300. The median spectrum has a signal-to-noise
ratio of per resolution element at 5000 \AA . As such, the MEGaSaURA
spectra have superior signal-to-noise-ratio and wavelength coverage compared to
what COS/HST provides for starburst galaxies in the local universe. This paper
describes the sample, the observations, and the data reduction. We compare the
measured redshifts for the stars, the ionized gas as traced by nebular lines,
and the neutral gas as traced by absorption lines; we find the expected bulk
outflow of the neutral gas, and no systemic offset between the redshifts
measured from nebular lines and the redshifts measured from the stellar
continuum. We provide the MEGaSaURA spectra to the astronomical community
through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal
publication. v2 addresses minor comments from refere
Recovering Stellar Population Properties and Redshifts from Broad-Band Photometry of Simulated Galaxies: Lessons for SED Modeling
We present a detailed analysis of our ability to determine stellar masses,
ages, reddening and extinction values, and star formation rates of
high-redshift galaxies by modeling broad-band SEDs with stellar population
synthesis. In order to do so, we computed synthetic optical-to-NIR SEDs for
model galaxies taken from hydrodynamical merger simulations placed at redshifts
1.5 < z < 3. Viewed under different angles and during different evolutionary
phases, the simulations represent a wide variety of galaxy types (disks,
mergers, spheroids). We show that simulated galaxies span a wide range in SEDs
and color, comparable to these of observed galaxies. In all star-forming
phases, dust attenuation has a large effect on colors, SEDs, and fluxes. The
broad-band SEDs were then fed to a standard SED modeling procedure and
resulting stellar population parameters were compared to their true values.
Disk galaxies generally show a decent median correspondence between the true
and estimated mass and age, but suffer from large uncertainties. During the
merger itself, we find larger offsets (e.g., log M_recovered - log M_true =
-0.13^{+0.10}_{-0.14}). E(B-V) values are generally recovered well, but the
estimated total visual absorption Av is consistently too low, increasingly so
for larger optical depths. Since the largest optical depths occur during the
phases of most intense star formation, it is for the highest SFRs that we find
the largest underestimates. The masses, ages, E(B-V), Av, and SFR of merger
remnants (spheroids) are very well reproduced. We discuss possible biases in
SED modeling results caused by mismatch between the true and template star
formation history, dust distribution, metallicity variations and AGN
contribution.Comment: Accepted for publication in the Astrophysical Journal, 24 pages, 19
figure
The Majority of Compact Massive Galaxies at z~2 are Disk Dominated
We investigate the stellar structure of massive, quiescent galaxies at z~2,
based on Hubble Space Telescope/WFC3 imaging from the Early Release Science
program. Our sample of 14 galaxies has stellar masses of M* > 10^{10.8} Msol
and photometric redshifts of 1.5 < z < 2.5. In agreement with previous work,
their half-light radii are <2 kpc, much smaller than equally massive galaxies
in the present-day universe. A significant subset of the sample appears highly
flattened in projection, which implies, considering viewing angle statistics,
that a significant fraction of the galaxies in our sample have pronounced
disks. This is corroborated by two-dimensional surface brightness profile fits.
We estimate that 65% +/- 15% of the population of massive, quiescent z~2
galaxies are disk-dominated. The median disk scale length is 1.5 kpc,
substantially smaller than the disks of equally massive galaxies in the
present-day universe. Our results provide strong observational evidence that
the much-discussed ultra-dense high-redshift galaxies should generally be
thought of as disk-like stellar systems with the majority of stars formed from
gas that had time to settle into a disk.Comment: published versio
The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7
We present the KMOS^3D survey, a new integral field survey of over 600
galaxies at 0.7<z<2.7 using KMOS at the Very Large Telescope (VLT). The KMOS^3D
survey utilizes synergies with multi-wavelength ground and space-based surveys
to trace the evolution of spatially-resolved kinematics and star formation from
a homogeneous sample over 5 Gyrs of cosmic history. Targets, drawn from a
mass-selected parent sample from the 3D-HST survey, cover the star
formation-stellar mass () and rest-frame planes uniformly. We
describe the selection of targets, the observations, and the data reduction. In
the first year of data we detect Halpha emission in 191
Msun galaxies at z=0.7-1.1 and z=1.9-2.7. In
the current sample 83% of the resolved galaxies are rotation-dominated,
determined from a continuous velocity gradient and , implying
that the star-forming 'main sequence' (MS) is primarily composed of rotating
galaxies at both redshift regimes. When considering additional stricter
criteria, the Halpha kinematic maps indicate at least ~70% of the resolved
galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated
velocity dispersions reported in previous IFS studies at z>0.7. For
rotation-dominated disks, the average intrinsic velocity dispersion decreases
by a factor of two from 50 km/s at z~2.3 to 25 km/s at z~0.9 while the
rotational velocities at the two redshifts are comparable. Combined with
existing results spanning z~0-3, disk velocity dispersions follow an
approximate (1+z) evolution that is consistent with the dependence of velocity
dispersion on gas fractions predicted by marginally-stable disk theory.Comment: 20 pages, 11 figures, 1 Appendix; Accepted to ApJ November 2
On Sizes, Kinematics, M/L Gradients, and Light Profiles of Massive Compact Galaxies at z~2
We present a detailed analysis of the structure and resolved stellar
populations of simulated merger remnants, and compare them to observations of
compact quiescent galaxies at z ~ 2. We find that major merging is a viable
mechanism to produce systems of ~ 10^11 Msun and ~ 1 kpc size, provided the gas
fraction at the time of final coalescence is high (~ 40%), and provided that
the progenitors are compact star-forming galaxies, as expected at high
redshift. Their integrated spectral energy distributions and velocity
dispersions are in good agreement with the observations, and their position in
the (v_{maj}/sigma, ellipticity) diagram traces the upper envelope of the
distribution of lower redshift early-type galaxies. The simulated merger
remnants show time- and sightline-dependent M/L ratio gradients that result
from a superposition of radially dependent stellar age, stellar metallicity,
and extinction. The median ratio of effective radius in rest-frame V-band light
to that in mass surface density is ~ 2 during the quiescent remnant phase. This
is typically expressed by a negative color gradient (i.e., red core), which we
expect to correlate with the integrated color of the system. Finally, the
simulations differ from the observations in their surface brightness profile
shape. The simulated remnants are typically best fit by high (n >> 4) Sersic
indices, whereas observed quiescent galaxies at z ~ 2 tend to be less cuspy
(median n ~ 2.3). Limiting early star formation in the progenitors may be
required to prevent the simulated merger remnants from having extended wings.Comment: Accepted for publication in The Astrophysical Journal, 21 pages, 17
figure
Studying the impact of a medication use evaluation for polymedicated older patients by the community pharmacist (SIMENON) : study protocol
Background: Aged polymedicated patients are particularly vulnerable for drug-related problems. A medication review aims to optimize the medication use of patients and improve health outcomes. In this study, the effect of a pharmacist-led medication use review is investigated for polymedicated ambulatory older patients with the aim of implementing this pharmaceutical care intervention across Belgium.
Methods: This article describes the study protocol of the SIMENON study and reports the results of the feasibility study, which aimed to test and optimize this study protocol. In the SIMENON intervention study, 75 Belgian community pharmacies each recruit 12 patients for a medication use review. For each patient, the identified drug-related problems and subsequent interventions are registered using the PharmDISC classification. In a subset of Dutch speaking patients, a pretest-posttest single group design is used to measure the impact of this review on patient related outcomes using questionnaires. The main outcome of the study is the type and number of drug-related problems and related interventions. A second outcome is the impact of the medication use review on adherence, objectively measured with dispensing data. Evolution in medication related quality of life is another outcome, measured with the Living with Medicines Questionnaire version 3. Other patient reported outcomes include adherence, self-management, patient satisfaction, fall incidents and use of emergency healthcare services.
Discussion: The findings of this study can provide data on the effectiveness of a medication use review in the Belgian primary care setting. Furthermore, it will provide insights in which patients benefit most of this intervention and therefore facilitate the implementation of medication review in Belgium
The Detection of a Red Sequence of Massive Field Galaxies at z~2.3 and its Evolution to z~0
The existence of massive galaxies with strongly suppressed star formation at
z~2.3, identified in a previous paper, suggests that a red sequence may already
be in place beyond z=2. In order to test this hypothesis, we study the
rest-frame U-B color distribution of massive galaxies at 2<z<3. The sample is
drawn from our near-infrared spectroscopic survey for massive galaxies. The
color distribution shows a statistically significant (>3 sigma) red sequence,
which hosts ~60% of the stellar mass at the high-mass end. The red-sequence
galaxies have little or no ongoing star formation, as inferred from both
emission-line diagnostics and stellar continuum shapes. Their strong Balmer
breaks and their location in the rest-frame U-B, B-V plane indicate that they
are in a post-starburst phase, with typical ages of ~0.5-1.0 Gyr. In order to
study the evolution of the red sequence, we compare our sample with
spectroscopic massive galaxy samples at 0.02<z<0.045 and 0.6<z<1.0. The
rest-frame U-B color reddens by ~0.25 mag from z~2.3 to the present at a given
mass. Over the same redshift interval, the number and stellar mass density on
the high-mass end (>10^11 Msol) of the red sequence grow by factors of ~8 and
~6, respectively. We explore simple models to explain the observed evolution.
Passive evolution models predict too strong d(U-B), and produce z~0 galaxies
that are too red. More complicated models that include aging, galaxy
transformations, and red mergers can explain both the number density and color
evolution of the massive end of the red sequence between z~2.3 and the present.Comment: Accepted for publication in the Astrophysical Journa
What turns galaxies off? The different morphologies of star-forming and quiescent galaxies since z~2 from CANDELS
We use HST/WFC3 imaging from the CANDELS Multicycle Treasury Survey, in
conjunction with the Sloan Digital Sky Survey, to explore the evolution of
galactic structure for galaxies with stellar masses >3e10M_sun from z=2.2 to
the present epoch, a time span of 10Gyr. We explore the relationship between
rest-frame optical color, stellar mass, star formation activity and galaxy
structure. We confirm the dramatic increase from z=2.2 to the present day in
the number density of non-star-forming galaxies above 3e10M_sun reported by
others. We further find that the vast majority of these quiescent systems have
concentrated light profiles, as parametrized by the Sersic index, and the
population of concentrated galaxies grows similarly rapidly. We examine the
joint distribution of star formation activity, Sersic index, stellar mass,
inferred velocity dispersion, and stellar surface density. Quiescence
correlates poorly with stellar mass at all z<2.2. Quiescence correlates well
with Sersic index at all redshifts. Quiescence correlates well with `velocity
dispersion' and stellar surface density at z>1.3, and somewhat less well at
lower redshifts. Yet, there is significant scatter between quiescence and
galaxy structure: while the vast majority of quiescent galaxies have prominent
bulges, many of them have significant disks, and a number of bulge-dominated
galaxies have significant star formation. Noting the rarity of quiescent
galaxies without prominent bulges, we argue that a prominent bulge (and
perhaps, by association, a supermassive black hole) is an important condition
for quenching star formation on galactic scales over the last 10Gyr, in
qualitative agreement with the AGN feedback paradigm.Comment: The Astrophysical Journal, in press; 20 pages with 13 figure
- …