179 research outputs found
The SWELLS Survey. VI. hierarchical inference of the initial mass functions of bulges and discs
The long-standing assumption that the stellar initial mass function (IMF) is
universal has recently been challenged by a number of observations. Several
studies have shown that a "heavy" IMF (e.g., with a Salpeter-like abundance of
low mass stars and thus normalisation) is preferred for massive early-type
galaxies, while this IMF is inconsistent with the properties of less massive,
later-type galaxies. These discoveries motivate the hypothesis that the IMF may
vary (possibly very slightly) across galaxies and across components of
individual galaxies (e.g. bulges vs discs). In this paper we use a sample of 19
late-type strong gravitational lenses from the SWELLS survey to investigate the
IMFs of the bulges and discs in late-type galaxies. We perform a joint analysis
of the galaxies' total masses (constrained by strong gravitational lensing) and
stellar masses (constrained by optical and near-infrared colours in the context
of a stellar population synthesis [SPS] model, up to an IMF normalisation
parameter). Using minimal assumptions apart from the physical constraint that
the total stellar mass within any aperture must be less than the total mass
within the aperture, we find that the bulges of the galaxies cannot have IMFs
heavier (i.e. implying high mass per unit luminosity) than Salpeter, while the
disc IMFs are not well constrained by this data set. We also discuss the
necessity for hierarchical modelling when combining incomplete information
about multiple astronomical objects. This modelling approach allows us to place
upper limits on the size of any departures from universality. More data,
including spatially resolved kinematics (as in paper V) and stellar population
diagnostics over a range of bulge and disc masses, are needed to robustly
quantify how the IMF varies within galaxies.Comment: Accepted for publication in MNRAS. 15 pages, 8 figures. Code
available at https://github.com/eggplantbren/SWELLS_Hierarchica
The SWELLS survey. IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy
We construct a fully self-consistent mass model for the lens galaxy J2141 at
z=0.14, and use it to improve on previous studies by modelling its
gravitational lensing effect, gas rotation curve and stellar kinematics
simultaneously. We adopt a very flexible axisymmetric mass model constituted by
a generalized NFW dark matter halo and a stellar mass distribution obtained by
deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of
the galaxy, with the (spatially constant) M/L ratio as a free parameter. We
model the stellar kinematics by solving the anisotropic Jeans equations. We
find that the inner logarithmic slope of the dark halo is weakly constrained
(gamma = 0.82^{+0.65}_{-0.54}), and consistent with an unmodified NFW profile.
We infer the galaxy to have (i) a dark matter fraction within 2.2 disk radii of
0.28^{+0.15}_{-0.10}, independent of the galaxy stellar population, implying a
maximal disk for J2141; (ii) an apparently uncontracted dark matter halo, with
concentration c_{-2} = 7.7_{-2.5}^{+4.2} and virial velocity v_{vir} =
242_{-39}^{+44} km/s, consistent with LCDM predictions; (iii) a slightly oblate
halo (q_h = 0.75^{+0.27}_{-0.16}), consistent with predictions from
baryon-affected models. Comparing the stellar mass inferred from the combined
analysis (log_{10} Mstar/Msun = 11.12_{-0.09}^{+0.05}) with that inferred from
SPS modelling of the galaxies colours, and accounting for a cold gas fraction
of 20+/-10%, we determine a preference for a Chabrier IMF over Salpeter IMF by
a Bayes factor of 5.7 (substantial evidence). We infer a value beta_{z} = 1 -
sigma^2_{z}/sigma^2_{R} = 0.43_{-0.11}^{+0.08} for the orbital anisotropy
parameter in the meridional plane, in agreement with most studies of local disk
galaxies, and ruling out at 99% CL that the dynamics of this system can be
described by a two-integral distribution function. [Abridged]Comment: Accepted for publication in MNRAS. 17 pages, 9 figure
The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies
The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres
Short-range ordering in a battery electrode, the 'cation-disordered' rocksalt Li1.25Nb0.25Mn0.5O2.
Cation order, with a local structure related to γ-LiFeO2, is observed in the nominally cation-disordered Li-excess rocksalt Li1.25Nb0.25Mn0.5O2via X-ray diffraction, neutron pair distribution function analysis, magnetic susceptibility and NMR spectroscopy. The correlation length of ordering depends on synthesis conditions and has implications for the electrochemistry of these phases.EPSRC: EP/L015978/1
Basic Energy Science, US Department of Energy: DE-SC001258
The SWELLS survey. III. Disfavouring "heavy" initial mass functions for spiral lens galaxies
We present gravitational lens models for 20 strong gravitational lens systems
observed as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS)
project. Fifteen of the lenses are taken from paper I while five are newly
discovered systems. The systems are galaxy-galaxy lenses where the foreground
deflector has an inclined disc, with a wide range of morphological types, from
late-type spiral to lenticular. For each system, we compare the total mass
inside the critical curve inferred from gravitational lens modelling to the
stellar mass inferred from stellar population synthesis (SPS) models, computing
the stellar mass fraction f* = M(SPS)/M(lens). We find that, for the lower mass
SWELLS systems, adoption of a Salpeter stellar initial mass function (IMF)
leads to estimates of f* that exceed 1. This is unphysical, and provides strong
evidence against the Salpeter IMF being valid for these systems. Taking the
lower mass end of the SWELLS sample sigma(SIE) < 230 km/s, we find that the IMF
is lighter (in terms of stellar mass-to-light ratio) than Salpeter with 98%
probability, and consistent with the Chabrier IMF and IMFs between the two.
This result is consistent with previous studies of spiral galaxies based on
independent techniques. In combination with recent studies of massive
early-type galaxies that have favoured a heavier Salpeter-like IMF, this result
strengthens the evidence against a universal stellar IMF.Comment: Accepted for publication in MNRAS. Some changes (none major) to
address the referee's comments. 18 pages, 8 figure
EnROL: A multicentre randomised trial of conventional versus laparoscopic surgery for colorectal cancer within an enhanced recovery programme
BACKGROUND: During the last two decades the use of laparoscopic resection and a multimodal approach known as an enhanced recovery programme, have been major changes in colorectal perioperative care. Clinical outcome improves using laparoscopic surgery to resect colorectal cancer but until recently no multicentre trial evidence had been reported regarding whether the benefits of laparoscopy still exist when open surgery is optimized within an enhanced recovery programme. The EnROL trial (Enhanced Recovery Open versus Laparoscopic) examines the hypothesis that laparoscopic surgery within an enhanced recovery programme will provide superior postoperative outcomes when compared to conventional open resection of colorectal cancer within the same programme. METHODS/DESIGN: EnROL is a phase III, multicentre, randomised trial of laparoscopic versus open resection of colon and rectal cancer with blinding of patients and outcome observers to the treatment allocation for the first 7 days post-operatively, or until discharge if earlier. 202 patients will be recruited at approximately 12 UK hospitals and randomised using minimization at a central computer system in a 1:1 ratio. Recruiting surgeons will previously have performed >100 laparoscopic colorectal resections and >50 open total mesorectal excisions to minimize conversion. Eligible patients are those suitable for elective resection using either technique. Excluded patients include: those with acute intestinal obstruction and patients in whom conversion from laparoscopic to open procedure is likely. The primary outcome is physical fatigue as measured by the physical fatigue domain of the multidimensional fatigue inventory 20 (MFI-20) with secondary outcomes including postoperative hospital stay; complications; reoperation and readmission; quality of life indicators; cosmetic assessments; standardized performance indicators; health economic analysis; the other four domains of the MFI-20. Pathological assessment of surgical quality will also be undertaken and compliance with the enhanced recovery programme will be recorded for all patients. DISCUSSION: Should this trial demonstrate that laparoscopic surgery confers a significant clinical and/or health economic benefit this will further support the transition to this type of surgery, with implications for the training of surgeons and resource allocation. TRIAL REGISTRATION: ISRCTN48516968
The SWELLS survey. II. Breaking the disk-halo degeneracy in the spiral galaxy gravitational lens SDSS J2141-0001
The degeneracy among the disk, bulge and halo contributions to galaxy
rotation curves prevents an understanding of the distribution of baryons and
dark matter in disk galaxies. In an attempt to break this degeneracy, we
present an analysis of the spiral galaxy strong gravitational lens SDSS
J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space
Telescope multicolor imaging, gas and stellar kinematics data derived from
long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the
Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bulge,
disk and halo components and infer the contribution of each component, using
information from gravitational lensing and gas kinematics. This analysis yields
a best-fitting total (disk plus bulge) stellar mass of log_{10}(Mstar/Msun) =
10.99(+0.11,-0.25). The photometric data combined with stellar population
synthesis models yield log_{10}(Mstar/Msun) = 10.97\pm0.07, and 11.21\pm0.07
for the Chabrier and Salpeter IMFs, respectively. Accounting for the expected
gas fraction of \simeq 20% reduces the lensing plus kinematics stellar mass by
0.10\pm0.05 dex, resulting in a Bayes factor of 11.9 in favor of a Chabrier
IMF. The dark matter halo is roughly spherical, with minor to major axis ratio
q_{halo}=0.91(+0.15,-0.13). The dark matter halo has a maximum circular
velocity of V_{max}=276(+17,-18) km/s, and a central density parameter of
log_{10}\Delta_{V/2}=5.9(+0.9,-0.5). This is higher than predicted for
uncontracted dark matter haloes in LCDM cosmologies, log_{10}\Delta_{V/2}=5.2,
suggesting that either the halo has contracted in response to galaxy formation,
or that the halo has a higher than average concentration. At 2.2 disk scale
lengths the dark matter fraction is f_{DM}=0.55(+0.20,-0.15), suggesting that
SDSS J2141-0001 is sub-maximal.Comment: 24 pages, 20 figures, accepted to MNRAS, minor change
The slope of the mass profile and the tilt of the fundamental plane in early-type galaxies
We present a survey, using the Chandra X-ray observatory, of the central
gravitating mass profiles in a sample of 10 galaxies, groups and clusters,
spanning ~2 orders of magnitude in virial mass. We find the total mass
distributions from ~0.2--10Re, where Re is the optical effective radius of the
central galaxy, are remarkably similar to powerlaw density profiles. The
negative logarithmic slope of the mass density profiles, alpha, systematically
varies with Re, from alpha=2, for systems with Re~4kpc to alpha=1.2 for systems
with Re>30kpc. Departures from hydrostatic equilibrium are likely to be small
and cannot easily explain this trend. We show that the conspiracy between the
baryonic (Sersic) and dark matter (NFW/ Einasto) components required to
maintain a powerlaw total mass distribution naturally predicts an
anti-correlation between alpha and Re that is very close to what is observed.
The systematic variation of alpha with Re implies a dark matter fraction within
Re that varies systematically with the properties of the galaxy in such a
manner as to reproduce, without fine tuning, the observed tilt of the
fundamental plane. We speculate that establishing a nearly powerlaw total mass
distribution is therefore a fundamental feature of galaxy formation and the
primary factor which determines the tilt of the fundamental plane.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in MNRAS.
Minor revisions to match accepted versio
MORE CARE Overview
International audienceThis paper provides an overview of MORE CARE, a European R&D project financed within the 5th Framework Energy Programme. This project has as main objective the development of an advanced control software system, aiming to optimize the overall performance of isolated and weakly interconnected systems in liberalized market environments by increasing the share of wind energy and other renewable forms, including advanced on-line security functions. The main features of the control system comprise advanced software modules for load and wind power forecasting, unit commitment and economic dispatch of the conventional and renewable units and on-line security assessment capabilities integrated in a friendly Man-Machine environment. Pilot installations of advanced control functions are foreseen on the islands of Crete, Ireland and Madeira
The SWELLS survey:V. A Salpeter stellar initial mass function in the bulges of massive spiral galaxies
Recent work has suggested that the stellar initial mass function (IMF) is not universal, but rather is correlated with galaxy stellar mass, stellar velocity dispersion or morphological type. In this paper, we investigate variations of the IMF within individual galaxies. For this purpose, we use strong lensing and gas kinematics to measure independently the normalization of the IMF of the bulge and disc components of a sample of five massive spiral galaxies with substantial bulge components taken from the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). We find that the stellar masses of the bulges are tightly constrained by the lensing and kinematic data. A comparison with masses based on stellar population synthesis models fitted to optical and near-infrared photometry favours a Salpeter-like normalization of the IMF. Conversely, the disc masses are less well constrained due to degeneracies with the dark matter halo, but are consistent with Milky Way-type IMFs in agreement with previous studies. The discs are submaximal at 2.2 disc scale lengths, but due to the contribution of the bulges, the galaxies are baryon dominated at 2.2 disc scale lengths. Globally, our inferred IMF normalization is consistent with that found for early-type galaxies of comparable stellar mass (>10(11) M-circle dot). Our results suggest a non-universal IMF within the different components of spiral galaxies, adding to the well-known differences in stellar populations between discs and bulges
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