Systematic trends in total-mass profiles from dynamical models of early-type galaxies

We study trends in the slope of the total mass profiles and dark matter fractions within the central half-light radius of 258 early-type galaxies, using data from the volume-limited ATLAS$^{\mathrm{3D}}$ survey. We use three distinct sets of dynamical models, which vary in their assumptions and also allow for spatial variations in the stellar mass-to-light ratio, to test the robustness of our results. We confirm that the slopes of the total mass profiles are approximately isothermal, and investigate how the total-mass slope depends on various galactic properties. The most statistically-significant correlations we find are a function of either surface density, $\Sigma_e$, or velocity dispersion, $\sigma_e$. However there is evidence for a break in the latter relation, with a nearly universal logarithmic slope above \log_{10}[\sigma_e/(\si{km~s^{-1}})]\sim 2.1 and a steeper trend below this value. For the 142 galaxies above that critical $\sigma_e$ value, the total mass-density logarithmic slopes have a mean value $\left\langle\gamma^\prime\right\rangle = -2.192 \pm 0.016$ ($1\sigma$ error) with an observed rms scatter of only $\sigma_{\gamma^\prime}=0.167 \pm 0.016$. Considering the observational errors, we estimate an intrinsic scatter of $\sigma_{\gamma^\prime}^\mathrm{intr} \approx 0.15$. These values are broadly consistent with those found by strong lensing studies at similar radii and agree, within the tight errors, with values recently found at much larger radii via stellar dynamics or HI rotation curves (using significantly smaller samples than this work).Comment: 17 pages, 11 figures, 3 tables. Published in MNRA

Do Job Security Guarantees Work?

We investigate the effect of employer job security guarantees on employee perceptions of job security. Using linked employer-employee data from the 1998 British Workplace Employee Relations Survey, we find job security guarantees reduce employee perceptions of job insecurity. This finding is robust to endogenous selection of job security guarantees by employers engaging in organisational change and workforce reductions. Furthermore, there is no evidence that increased job security through job guarantees results in greater work intensification, stress, or lower job satisfaction

Mathematical theory of the Goddard trajectory determination system

Basic mathematical formulations depict coordinate and time systems, perturbation models, orbital estimation techniques, observation models, and numerical integration methods

VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO

We present high spatial resolution near-infrared spectra and images of the nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K- and 0.11" in H-band, four times higher than previous studies. The observed gas motions suggest a kinematically hot disk which is orbiting a central object and is oriented nearly perpendicular to the nuclear jet. We model the central rotation and velocity dispersion curves of the [FeII] gas orbiting in the combined potential of the stellar mass and the (dominant) black hole. Our physically most plausible model, a dynamically hot and geometrically thin gas disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the physical state of the gas is not well understood, we also consider two limiting cases: first a cold disk model, which completely neglects the velocity dispersion; it yields an M_bh estimate that is almost two times lower. The other extreme case is to model a spherical gas distribution in hydrostatic equilibrium through Jeans equation. Compared to the hot disk model the best-fit black hole mass increases by a factor of 1.5. This wide mass range spanned by the limiting cases shows how important the gas physics is even for high resolution data. Our overall best-fitting black hole mass is a factor of 2-4 lower than previous measurements. With our revised M_bh estimate, Cen A's offset from the M_bh-sigma relation is significantly reduced; it falls above this relation by a factor of ~2, which is close to the intrinsic scatter of this relation. (Abridged)Comment: 12 pages, 14 figures, including minor changes following the referee report; accepted for publication in The Astrophysical Journa

A black-hole mass measurement from molecular gas kinematics in NGC4526

The masses of the supermassive black-holes found in galaxy bulges are correlated with a multitude of galaxy properties, leading to suggestions that galaxies and black-holes may evolve together. The number of reliably measured black-hole masses is small, and the number of methods for measuring them is limited, holding back attempts to understand this co-evolution. Directly measuring black-hole masses is currently possible with stellar kinematics (in early-type galaxies), ionised-gas kinematics (in some spiral and early-type galaxies) and in rare objects which have central maser emission. Here we report that by modelling the effect of a black-hole on the kinematics of molecular gas it is possible to fit interferometric observations of CO emission and thereby accurately estimate black hole masses. We study the dynamics of the gas in the early-type galaxy NGC4526, and obtain a best fit which requires the presence of a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit). With next generation mm-interferometers (e.g. ALMA) these observations could be reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing time. The use of molecular gas as a kinematic tracer should thus allow one to estimate black-hole masses in hundreds of galaxies in the local universe, many more than accessible with current techniques.Comment: To appear in Nature online on 30/01/2013. 3 Pages, 2 Figures (plus two pages of supplementary information

The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions

The mean ages of early-type galaxies obtained from the analysis of optical spectra, give a mean age of 8 Gyr at z = 0, with 40% being younger than 6 Gyr. Independent age determinations are possible by using infrared spectra (5-21 microns), which we have obtained with the Infrared Spectrograph on the Spitzer Observatory. This age indicator is based on the collective mass loss rate of stars, where mass loss from AGB stars produces a silicate emission feature at 9-12 microns. This feature decreases more rapidly than the shorter wavelength continuum as a stellar population ages, providing an age indicator. From observations of 30 nearby early-type galaxies, 29 show a spectral energy distribution dominated by stars and one has significant emission from the ISM and is excluded. The infrared age indicators for the 29 galaxies show them all to be old, with a mean age of about 10 Gyr and a standard deviation of only a few Gyr. This is consistent with the ages inferred from the values of M/L_B, but is inconsistent with the ages derived from the optical line indices, which can be much younger. All of these age indicators are luminosity-weighted and should be correlated, even if multiple-age components are considered. The inconsistency indicates that there is a significant problem with either the infrared and the M/L_B ages, which agree, or with the ages inferred from the optical absorption lines.Comment: Accepted for publication in Ap

A SAURON study of dwarf elliptical galaxies in the Virgo Cluster

Dwarf elliptical galaxies are the most common galaxy type in nearby galaxy clusters, yet they remain relatively poorly studied objects and many of their basic properties have yet to be quantified. In this contribution we present the preliminary results of a study of 4 Virgo and 1 field galaxy obtained with the SAURON integral field unit on the William Herschel Telescope (La Palma). While traditional long-slit observations are likely to miss more complicated kinematic features, with SAURON we are able to study both kinematics and stellar populations in two dimensions, obtaining a much more detailed view of the mass distribution and star formation histories.Comment: 2 pages, 1 figure; to appear in the proceedings of the conference "A Universe of dwarf galaxies" (Lyon, June 14-18, 2010

The benchmark black hole in NGC 4258: dynamical models from high-resolution two-dimensional stellar kinematics

NGC 4258 is the galaxy with the most accurate (maser-based) determination for the mass of the supermassive black hole (SMBH) in its nucleus. In this work we present a two-dimensional mapping of the stellar kinematics in the inner 3.0 x 3.0 arcsec = 100 x 100 pc of NGC 4258 using adaptative-optics observations obtained with the Near-Infrared Integral Field Spectrograph of the GEMINI North telescope at a 0.11 arcsec (4 pc) angular resolution. The observations resolve the radius of influence of the SMBH, revealing an abrupt increase in the stellar velocity dispersion within 10 pc from the nucleus, consistent with the presence of a SMBH there. Assuming that the galaxy nucleus is in a steady state and that the velocity dispersion ellipsoid is aligned with a cylindrical coordinate system, we constructed a Jeans anisotropic dynamical model to fit the observed kinematics distribution. Our dynamical model assumes that the galaxy has axial symmetry and is constructed using the multi-gaussian expansion method to parametrize the observed surface brightness distribution. The Jeans dynamical model has three free parameters: the mass of the central SMBH, the mass-luminosity ratio of the galaxy and the anisotropy of the velocity distribution. We test two types of models: one with constant velocity anisotropy, and another with variable anisotropy. The model that best reproduces the observed kinematics was obtained considering that the galaxy has radially varying anisotropy, being the best-fitting parameters with 3$\sigma$ significance $M_\bullet=4.8^{+0.8}_{-0.9}\times 10^7\,{\rm M_\odot}$ and $\Gamma_k = 4.1^{+0.4}_{-0.5}$. This value for the mass of the SMBH is just 25 per cent larger than that of the maser determination and 50 per cent larger that a previous stellar dynamical determination obtained via Schwarzschild models.Comment: Accepted for publication in MNRAS, 19 pages, 19 figure

Spatial kinematics of Brightest Cluster Galaxies and their close companions from Integral Field Unit spectroscopy

We present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) at z~0.1. Three of the BCGs have close companions within a projected radius of 20 kpc and one has no companion within that radius. We calculate the dynamical masses of the BCGs and their companions to be 1.4x10^11<M_dyn (M_solar)<1.5x10^12. We estimate the probability that the companions of the BCGs are bound using the observed masses and velocity offsets. We show that the lowest mass companion (1:4) is not bound while the two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs continue to grow from major merging even at z~0. We analyse the stellar kinematics of these systems using the \lambda_R parameter developed by the SAURON team. This offers a new and unique means to measure the stellar angular momentum of BCGs and make a direct comparison to other early-type galaxies. The BCGs and their companions have similar ellipticities to those of other early-type galaxies but are more massive. We find that not all these massive galaxies have low \lambda_R_e as one might expect. One of the four BCGs and the two massive companions are found to be fast-rotating galaxies with high angular momentum, thereby providing a new test for models of galaxy evolution and the formation of Intra-Cluster Light.Comment: 5 pages. Accepted for publication in MNRAS Letter

Musculoskeletal Geometry, Muscle Architecture and Functional Specialisations of the Mouse Hindlimb

Mice are one of the most commonly used laboratory animals, with an extensive array of disease models in existence, including for many neuromuscular diseases. The hindlimb is of particular interest due to several close muscle analogues/homologues to humans and other species. A detailed anatomical study describing the adult morphology is lacking, however. This study describes in detail the musculoskeletal geometry and skeletal muscle architecture of the mouse hindlimb and pelvis, determining the extent to which the muscles are adapted for their function, as inferred from their architecture. Using I2KI enhanced microCT scanning and digital segmentation, it was possible to identify 39 distinct muscles of the hindlimb and pelvis belonging to nine functional groups. The architecture of each of these muscles was determined through microdissections, revealing strong architectural specialisations between the functional groups. The hip extensors and hip adductors showed significantly stronger adaptations towards high contraction velocities and joint control relative to the distal functional groups, which exhibited larger physiological cross sectional areas and longer tendons, adaptations for high force output and elastic energy savings. These results suggest that a proximo-distal gradient in muscle architecture exists in the mouse hindlimb. Such a gradient has been purported to function in aiding locomotor stability and efficiency. The data presented here will be especially valuable to any research with a focus on the architecture or gross anatomy of the mouse hindlimb and pelvis musculature, but also of use to anyone interested in the functional significance of muscle design in relation to quadrupedal locomotion