204 research outputs found
The Three-Dimensional Mass Distribution in NGC 1700
A variety of modeling techniques is used with surface photometry from the
literature and recently acquired high-accuracy stellar kinematic data to
constrain the three-dimensional mass distribution in the luminous cuspy
elliptical galaxy NGC 1700. First, we model the radial velocity field and
photometry, and, using a Bayesian technique, estimate the triaxiality T and
short-to-long axis ratio c in five concentric annuli between approximately 1
and 3 effective radii. The results are completely consistent with T being
constant inside about 2.5 r_e (36 arcsec; 6.7/h kpc). Adding an assumption of
constant T as prior information gives an upper limit of T < 0.16 (95%
confidence); this relaxes to T < 0.22 if it is also assumed that there is
perfect alignment between the angular momentum and the galaxy's intrinsic short
axis. Near axisymmetry permits us then to use axisymmetric models to constrain
the radial mass profile. Using the Jeans (moment) equations, we demonstrate
that 2-integral, constant-M/L models cannot fit the data; but a 2-integral
model in which the cumulative enclosed M/L increases by a factor of roughly 2
from the center out to 12/h kpc can. Three-integral models constructed by
quadratic programming show that, in fact, no constant-M/L model is consistent
with the kinematics. Anisotropic 3-integral models with variable M/L, while not
uniquely establishing a minimum acceptable halo mass, imply, as do the moment
models, a cumulative M/L_B approximately 10 h at 12/h kpc. We conclude that NGC
1700 represents the best stellar dynamical evidence to date for dark matter in
elliptical galaxies.Comment: 26 pages, Latex, AASTeX v4.0, with 11 eps figures. To appear in The
Astronomical Journal, January 1999. Figures 1 and 3 are color but are
readable in b/
The puzzlingly large Ca II triplet absorption in dwarf elliptical galaxies
We present central CaT, PaT, and CaT* indices for a sample of fifteen dwarf
elliptical galaxies (dEs). Twelve of these have CaT* ~ 7 A and extend the
negative correlation between the CaT* index and central velocity dispersion
sigma, which was derived for bright ellipticals (Es), down to 20 < sigma < 55
km/s. For five dEs we have independent age and metallicity estimates. Four of
these have CaT* ~ 7 A, much higher than expected from their low metallicities
(-1.5 < [Z/H] < -0.5). The observed anti-correlation of CaT* as a function of
sigma or Z is in flagrant disagreement with theory. We discuss some of the
amendments that have been proposed to bring the theoretical predictions into
agreement with the observed CaT*-values of bright Es and how they can be
extended to incorporate also the observed CaT*-values of dEs. Moreover, 3 dEs
in our sample have CaT* ~ 5 A, as would be expected for metal-poor stellar
systems. Any theory for dE evolution will have to be able to explain the
co-existence of low-CaT* and high-CaT* dEs at a given mean metallicity. This
could be the first direct evidence that the dE population is not homogeneous,
and that different evolutionary paths led to morphologically and kinematically
similar but chemically distinct objects.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Keplerian discs around post-AGB stars: a common phenomenon?
Aims: We aim at showing that the broad-band SED characteristics of our sample
of post-AGB stars are best interpreted, assuming the circumstellar dust is
stored in Keplerian rotating passive discs.
Methods: We present a homogeneous and systematic study of the Spectral Energy
Distributions (SEDs) of a sample of 51 post-AGB objects. The selection criteria
to define the whole sample were tuned to cover the broad-band characteristics
of known binary post-AGB stars. The whole sample includes 20 dusty RV Tauri
stars from the General Catalogue of Variable Stars (GCVS). We supplemented our
own Geneva optical photometry with literature data to cover a broad range of
fluxes from the UV to the far-IR.
Results: All the SEDs display very similar characteristics: a large IR excess
with a dust excess starting near the sublimation temperature, irrespective of
the effective temperature of the central star. Moreover, when available, the
long wavelength fluxes show a black-body slope indicative of the presence of a
component of large mm sized grains.
Conclusions: We argue that in all systems, gravitationally bound dusty discs
are present. The discs must be puffed-up to cover a large opening angle for the
central star and we argue that the discs have some similarity with the passive
discs detected around young stellar objects. We interpret the presence of a
disc to be a signature for binarity of the central object, but this will need
confirmation by long-term monitoring of the radial velocities. We argue that
dusty RV Tauri stars are those binaries which happen to be in the Population II
instability strip.Comment: 29 pages, 5 figures, accepted for publication in A&
Kinematics of elliptical galaxies with a diffuse dust component
Observations show that early-type galaxies contain a considerable amount of
interstellar dust, most of which is believed to exist as a diffusely
distributed component. We construct a four-parameter elliptical galaxy model in
order to investigate the effects of such a smooth absorbing component on the
projection of kinematic quantities, such as the line profiles and their
moments. We investigate the dependence on the optical depth and on the dust
geometry. Our calculations show that both the amplitude and the morphology of
these quantities can be significantly affected. Dust effects should therefore
be taken in consideration when interpreting photometric and kinematic
properties, and correlations that utilize these quantities.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Generalisations of the Tully-Fisher relation for early and late-type galaxies
We study the locus of dwarf and giant early and late-type galaxies on the
Tully-Fisher relation (TFR), the stellar mass Tully-Fisher relation (sTFR) and
the so-called baryonic or HI gas+stellar mass Tully-Fisher relation (gsTFR). We
show that early-type and late-type galaxies, from dwarfs to giants, trace
different yet approximately parallel TFRs. Surprisingly, early-type and
late-type galaxies trace a single yet curved sTFR over a range of 3.5 orders of
magnitude in stellar mass. Moreover, all galaxies trace a single, linear gsTFR,
over 3.5 orders of magnitude in HI gas+stellar mass. Dwarf ellipticals,
however, lie slightly below the gsTFR. This may indicate that early-type
dwarfs, contrary to the late-types, have lost their gas, e.g. by galactic winds
or ram-pressure stripping. Overall, environment only plays a secondary role in
shaping these relations, making them a rather ``clean'' cosmological tool. LCDM
simulations predict roughly the correct slopes for these relations.Comment: 4 pages, 2 figures, accepted for publication in Astrophysical Journa
Observational evidence for a connection between supermassive black holes and dark matter haloes
We present new velocity dispersion measurements of sample of 12 spiral
galaxies for which extended rotation curves are available. These data are used
to refine a recently discovered correlation between the circular velocity and
the central velocity dispersion of spiral galaxies. We find a slightly steeper
slope for our larger sample, we confirm the negligible intrinsic scatter on
this correlation, and we find a striking agreement with a corresponding
relation for elliptical galaxies. We combine this correlation with the
well-known MBH-sigma relation to obtain a tight correlation between the
circular velocities of galaxies and the masses of the supermassive black holes
they host. This correlation is the observational evidence for an intimate link
between dark matter haloes and supermassive black holes. Apart from being an
important ingredient for theoretical models of galaxy formation and evolution,
the relation between MBH and circular velocity can serve as a practical tool to
estimate black hole masses in spiral galaxies.Comment: 5 pages, 2 figures, accepted for publication in MNRAS pink page
Player migration and opportunity: examining the efficacy of the UEFA home-grown rule in six European football leagues.
The introduction of UEFAs home-grown rule occurred for the start of the 2006–2007 season with the full quota in place
from the 2008–2009 season, which imposed quotas on European clubs. From 2008, clubs are required to have at least 8
players classified as home-grown in the 25-player squad, up from 4 in 2006–2007 and 6 in 2007–2008. This study
examines the efficacy of this rule across the six major European leagues (England, France, Germany, Holland, Italy
and Spain) in relation to playing opportunities (minutes played and appearances) between 1999 and 2015. This was
also examined in relation to age. Since the home-grown rule was introduced for the six nations hosting the major
leagues, the rule had different impacts by nationality. Only Germany saw significant increases in the proportion of
minutes played by their players when comparing the periods before and after the home-grown rules were imposed.
Holland, albeit seeing a slight decrease overall, saw significant increases for playing time for under 21s and 22- to 25-year olds. England and Italy were the two nations where statistically significant decreases in indigenous playing opportunities were recorded since the home-grown rules were introduced
Embedded disks in Fornax dwarf ellipticals
We present photometric and kinematic evidence for the presence of stellar
disks, seen practically edge-on, in two Fornax dwarf galaxies, FCC204 (dS0(6))
and FCC288 (dS0(7)). This is the first time such structures have been
identified in Fornax dwarfs. FCC2088 has only a small bulge and a bright
flaring and slightly warped disk that can be traced out to 23" from the center
(2.05 kpc for H_0=75 km/s/Mpc). FCC204's disk can be traced out to 20" (1.78
kpc). This galaxy possesses a large bulge. These results can be compared to the
findings of Jerjen et al. (2000) and Barazza et al. (2002) who discovered
nucleated dEs with spiral and bar features in the Virgo Cluster.Comment: 8 pages, 8 figures, accepted for publication in A&
Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365
We present a flexible and efficient method to construct triaxial dynamical
models of galaxies with a central black hole, using Schwarzschild's orbital
superposition approach. Our method is general and can deal with realistic
luminosity distributions, which project to surface brightness distributions
that may show position angle twists and ellipticity variations. The models are
fit to measurements of the full line-of-sight velocity distribution (wherever
available). We verify that our method is able to reproduce theoretical
predictions of a three-integral triaxial Abel model. In a companion paper (van
de Ven, de Zeeuw & van den Bosch), we demonstrate that the method recovers the
phase-space distribution function. We apply our method to two-dimensional
observations of the E3 galaxy NGC 4365, obtained with the integral-field
spectrograph SAURON, and study its internal structure, showing that the
observed kinematically decoupled core is not physically distinct from the main
body and the inner region is close to oblate axisymmetric.Comment: 21 Pages, 14 (Colour) Figures, Companion paper is arXiv:0712.0309
Accepted to MNRAS. Full resolution version at
http://www.strw.leidenuniv.nl/~bosch/papers/RvdBosch_triaxmethod.pd
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