1,368 research outputs found
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 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, , or
velocity dispersion, . 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 value, the total
mass-density logarithmic slopes have a mean value
(
error) with an observed rms scatter of only . Considering the observational errors, we estimate an intrinsic scatter
of . 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
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
Fast and slow rotators in the densest environments: a FLAMES/GIRAFFE IFS study of galaxies in Abell 1689 at z=0.183
We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the
massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that
of ATLAS3D, we extend the baseline of the kinematic morphology-density relation
by an order of magnitude in projected density and show that it is possible to
use existing instruments to identify slow and fast rotators beyond the local
Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude
similar to those in the Virgo cluster. The overall slow rotator fraction of our
Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection
criteria. This suggests that the fraction of slow rotators in a cluster is not
strongly dependent on its density. However, within Abell 1689, we find that the
fraction of slow rotators increases towards the centre, as was also found in
the Virgo cluster.Comment: Accepted by MNRA
Made-to-measure galaxy models - II Elliptical and Lenticular Galaxies
We take a sample of 24 elliptical and lenticular galaxies previously analysed
by the SAURON project using three-integral dynamical models created with
Schwarzschild's method, and re-analyse them using the made-to-measure (M2M)
method of dynamical modelling. We obtain good agreement between the two methods
in determining the dynamical mass-to-light (M/L) ratios for the galaxies with
over 80% of ratios differing by < 10% and over 95% differing by < 20%. We show
that (M/L)_M2M is approximately equal to (M/L)_Sch. For the global velocity
dispersion anisotropy parameter delta, we find similar values but with fewer of
the made-to-measure models tangentially anisotropic by comparison with their
SAURON Schwarzschild counterparts. Our investigation is the largest comparative
application of the made-to-measure method to date.Comment: 14 pages, 8 figures and 5 table
SDSS-IV MaNGA: The intrinsic shape of slow rotator early-type galaxies
By inverting the distributions of galaxies' apparent ellipticities and
misalignment angles (measured around the projected half-light radius ) between their photometric and kinematic axes, we study the intrinsic shape
distribution of 189 slow rotator early-type galaxies with stellar masses
, extracted from a
sample of about 2200 galaxies with integral-field stellar kinematics from the
DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow
rotators, Graham+18 showed that there is clear structure in the misalignment
angle distribution, with two peaks at both and
misalignment (characteristic of oblate and prolate rotation respectively). Here
we invert the observed distribution from Graham+18. The large sample allows us
to go beyond the known fact that slow rotators are weakly triaxial and to place
useful constraints on their intrinsic triaxiality distribution (around ) for the first time. The shape inversion is generally non-unique. However,
we find that, for a wide set of model assumptions, the observed distribution
clearly requires a dominant triaxial-oblate population. For some of our models,
the data suggest a hint for a minor triaxial-prolate population, but a dominant
prolate population is ruled out.Comment: Accepted for publication in ApJL, 10 pages, 4 figures, 1 tabl
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?
We examine the properties of a morphologically-selected sample of 0.4<z<1.0
spheroidal galaxies in the GOODS fields in order to ascertain whether their
increase in abundance with time arises primarily from mergers. To address this
question we determine scaling relations between the dynamical mass determined
from stellar velocity dispersions, and the stellar mass determined from optical
and infrared photometry. We exploit these relations across the larger sample
for which we have stellar masses in order to construct the first statistically
robust estimate of the evolving dynamical mass function over 0<z<1. The trends
observed match those seen in the stellar mass functions of Bundy et al. 2005
regarding the top-down growth in the abundance of spheroidal galaxies. By
referencing our dynamical masses to the halo virial mass we compare the growth
rate in the abundance of spheroidals to that predicted by the assembly of dark
matter halos. Our comparisons demonstrate that major mergers do not fully
account for the appearance of new spheroidals since z~1 and that additional
mechanisms, such as morphological transformations, are required to drive the
observed evolution.Comment: Accepted to ApJL; New version corrects the Millennium merger
predictions--further details at
http://www.astro.utoronto.ca/~bundy/millennium
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
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
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