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