18,592 research outputs found
Satellite Kinematics II: The Halo Mass-Luminosity Relation of Central Galaxies in SDSS
The kinematics of satellite galaxies reflect the masses of the extended dark
matter haloes in which they orbit, and thus shed light on the mass-luminosity
relation (MLR) of their corresponding central galaxies. In this paper we select
a large sample of centrals and satellites from the Sloan Digital Sky Survey
(SDSS) and measure the kinematics (velocity dispersions) of the satellite
galaxies as a function of the -band luminosity of the central galaxies.
Using the analytical framework presented in Paper I, we use these data to infer
{\it both} the mean and the scatter of the MLR of central galaxies, carefully
taking account of selection effects and biases introduced by the stacking
procedure. As expected, brighter centrals on average reside in more massive
haloes. In addition, we find that the scatter in halo masses for centrals of a
given luminosity, , also increases with increasing luminosity.
As we demonstrate, this is consistent with , which reflects
the scatter in the conditional probability function , being
independent of halo mass. Our analysis of the satellite kinematics yields
, in excellent agreement with constraints from
clustering and group catalogues, and with predictions from a semi-analytical
model of galaxy formation. We thus conclude that the amount of stochasticity in
galaxy formation, which is characterized by , is well
constrained, is independent of halo mass, and is in good agreement with current
models of galaxy formation.Comment: 17 pages, 12 figures, MNRAS submitte
Satellite Kinematics I: A New Method to Constrain the Halo Mass-Luminosity Relation of Central Galaxies
Satellite kinematics can be used to probe the masses of dark matter haloes of
central galaxies. In order to measure the kinematics with sufficient
signal-to-noise, one uses the satellite galaxies of a large number of central
galaxies stacked according to similar properties (e.g., luminosity). However,
in general the relation between the luminosity of a central galaxy and the mass
of its host halo will have non-zero scatter. Consequently, this stacking
results in combining the kinematics of satellite galaxies in haloes of
different masses, which complicates the interpretation of the data. In this
paper we present an analytical framework to model satellite kinematics,
properly accounting for this scatter and for various selection effects. We show
that in the presence of scatter in the halo mass-luminosity relation, the
commonly used velocity dispersion of satellite galaxies can not be used to
infer a unique halo mass-luminosity relation. In particular, we demonstrate
that there is a degeneracy between the mean and the scatter of the halo
mass-luminosity relation. We present a new technique that can break this
degeneracy, and which involves measuring the velocity dispersions using two
different weighting schemes: host-weighting (each central galaxy gets the same
weight) and satellite-weighting (each central galaxy gets a weight proportional
to its number of satellites). The ratio between the velocity dispersions
obtained using these two weighting schemes is a strong function of the scatter
in the halo mass-luminosity relation, and can thus be used to infer a unique
relation between light and mass from the kinematics of satellite galaxies.Comment: 8 pages, 3 figures, MNRAS submitte
Maturing Satellite Kinematics into a Competitive Probe of the Galaxy-Halo Connection
The kinematics of satellite galaxies moving in a dark matter halo are a
direct probe of the underlying gravitational potential. Thus, the phase-space
distributions of satellites represent a powerful tool to determine the
galaxy-halo connection from observations. By stacking the signal of a large
number of satellite galaxies this potential can be unlocked even for haloes
hosting a few satellites on average. In this work, we test the impact of
various modelling assumptions on constraints derived from analysing satellite
phase-space distributions in the non-linear, 1-halo regime. We discuss their
potential to explain the discrepancy between average halo masses derived from
satellite kinematics and gravitational lensing previously reported.
Furthermore, we develop an updated, more robust analysis to extract constraints
on the galaxy-halo relation from satellite properties in spectroscopic galaxy
surveys such as the SDSS. We test the accuracy of this approach using a large
number of realistic mock catalogues. Furthermore, we find that constraints
derived from such an analysis are complementary and competitive with respect to
the commonly used galaxy clustering and galaxy-galaxy lensing observables.Comment: 24 pages, 15 figures; resubmitted to MNRAS after first referee repor
The effect of tides on the Sculptor dwarf spheroidal galaxy
Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter
dominated objects in the Universe. Their dynamical masses are commonly derived
using the kinematics of stars under the assumption of equilibrium. However,
these objects are satellites of massive galaxies (e.g.\ the Milky Way) and thus
can be influenced by their tidal fields. We investigate the implication of the
assumption of equilibrium focusing on the Sculptor dSph by means of ad-hoc
-body simulations tuned to reproduce the observed properties of Sculptor
following the evolution along some observationally motivated orbits in the
Milky Way gravitational field. For this purpose, we used state-of-the-art
spectroscopic and photometric samples of Sculptor's stars. We found that the
stellar component of the simulated object is not directly influenced by the
tidal field, while the mass of the more diffuse DM halo is
stripped. We conclude that, considering the most recent estimate of the
Sculptor proper motion, the system is not affected by the tides and the stellar
kinematics represents a robust tracer of the internal dynamics. In the
simulations that match the observed properties of Sculptor, the present-day
dark-to-luminous mass ratio is within the stellar half-light radius
( kpc) and within the maximum radius of the analysed dataset
( kpc).Comment: 19 pages, 10 figures, accepted for publication in MNRAS. V3: updated
after editor comments See our playlist for simulation videos:
https://av.tib.eu/series/633/supplemental+videos+of+the+paper+the+effect+of+tides+on+the+sculptor+dwarf+spheroidal+galax
IK-FA, a new heuristic inverse kinematics solver using firefly algorithm
In this paper, a heuristic method based on Firefly Algorithm is proposed for inverse kinematics problems in articulated robotics. The proposal is called, IK-FA. Solving inverse kinematics, IK, consists in finding a set of joint-positions allowing a specific point of the system to achieve a target position. In IK-FA, the Fireflies positions are assumed to be a possible solution for joints elementary motions. For a robotic system with a known forward kinematic model, IK-Fireflies, is used to generate iteratively a set of joint motions, then the forward kinematic model of the system is used to compute the relative Cartesian positions of a specific end-segment, and to compare it to the needed target position. This is a heuristic approach for solving inverse kinematics without computing the inverse model. IK-FA tends to minimize the distance to a target position, the fitness function could be established as the distance between the obtained forward positions and the desired one, it is subject to minimization. In this paper IK-FA is tested over a 3 links articulated planar system, the evaluation is based on statistical analysis of the convergence and the solution quality for 100 tests. The impact of key FA parameters is also investigated with a focus on the impact of the number of fireflies, the impact of the maximum iteration number and also the impact of (a, ß, ¿, d) parameters. For a given set of valuable parameters, the heuristic converges to a static fitness value within a fix maximum number of iterations. IK-FA has a fair convergence time, for the tested configuration, the average was about 2.3394 × 10-3 seconds with a position error fitness around 3.116 × 10-8 for 100 tests. The algorithm showed also evidence of robustness over the target position, since for all conducted tests with a random target position IK-FA achieved a solution with a position error lower or equal to 5.4722 × 10-9.Peer ReviewedPostprint (author's final draft
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