60 research outputs found
Measuring the slopes of mass profiles for dwarf spheroidals in triaxial CDM potentials
We generate stellar distribution functions (DFs) in triaxial haloes in order
to examine the reliability of slopes inferred by applying mass estimators of the form (i.e. assuming spherical symmetry, where and are
luminous effective radius and global velocity dispersion, respectively) to two
stellar sub-populations independently tracing the same gravitational potential.
The DFs take the form , are dynamically stable, and are generated within
triaxial potentials corresponding directly to subhaloes formed in cosmological
dark-matter-only simulations of Milky Way and galaxy cluster haloes.
Additionally, we consider the effect of different tracer number density
profiles (cuspy and cored) on the inferred slopes of mass profiles. For the
isotropic DFs considered here, we find that halo triaxiality tends to introduce
an anti-correlation between and when estimated for a variety of
viewing angles. The net effect is a negligible contribution to the systematic
error associated with the slope of the mass profile, which continues to be
dominated by a bias toward greater overestimation of masses for
more-concentrated tracer populations. We demonstrate that simple mass estimates
for two distinct tracer populations can give reliable (and cosmologically
meaningful) lower limits for , irrespective of the degree of
triaxiality or shape of the tracer number density profile.Comment: 5 pages, 4 figures, submitted to MNRA
The Growth in Size and Mass of Cluster Galaxies since z=2
We study the formation and evolution of Brightest Cluster Galaxies starting
from a population of quiescent ellipticals and following them to .
To this end, we use a suite of nine high-resolution dark matter-only
simulations of galaxy clusters in a CDM universe. We develop a scheme
in which simulation particles are weighted to generate realistic and
dynamically stable stellar density profiles at . Our initial conditions
assign a stellar mass to every identified dark halo as expected from abundance
matching; assuming there exists a one-to-one relation between the visible
properties of galaxies and their host haloes. We set the sizes of the luminous
components according to the observed relations for massive quiescent
galaxies. We study the evolution of the mass-size relation, the fate of
satellite galaxies and the mass aggregation of the cluster central. From ,
these galaxies grow on average in size by a factor 5 to 10 of and in mass by 2
to 3. The stellar mass growth rate of the simulated BCGs in our sample is of
1.9 in the range consistent with observations, and of 1.5 in the
range . Furthermore the satellite galaxies evolve to the present day
mass-size relation by . Assuming passively evolving stellar populations,
we present surface brightness profiles for our cluster centrals which resemble
those observed for the cDs in similar mass clusters both at and at .
This demonstrates that the CDM cosmology does indeed predict minor and
major mergers to occur in galaxy clusters with the frequency and mass ratio
distribution required to explain the observed growth in size of passive
galaxies since . Our experiment shows that Brightest Cluster Galaxies can
form through dissipationless mergers of quiescent massive galaxies,
without substantial additional star formation.Comment: submitted to MNRAS, 10 pages, 8 figures, 2 table
Weighing the Galactic disk using phase-space spirals III. Probing distant regions of the disk using the Gaia EDR3 proper motion sample
We have applied our method for weighing the Galactic disk using phase-space
spirals to the Gaia EDR3 proper motion sample. For stars in distant regions of
the Galactic disk, the latitudinal proper motion has a close projection with
vertical velocity, such that the phase-space spiral in the plane of vertical
position and vertical velocity can be observed without requiring that all stars
have available radial velocity information. We divided the Galactic plane into
360 separate data samples, each corresponding to an area cell in the Galactic
plane in the distance range of 1.4-3.4 kpc, with an approximate cell length of
200-400 pc. Roughly half of our data samples were disqualified altogether due
to severe selection effects, especially in the direction of the Galactic
centre. In the remainder, we were able to infer the vertical gravitational
potential by fitting an analytic model of the phase-space spiral to the data.
This work is the first of its kind, in the sense that we are weighing distant
regions of the Galactic disk with a high spatial resolution, without relying on
the strong assumptions of axisymmetry. Post-inference, we fit a thin disk scale
length of kpc, although this value is sensitive to the considered
spatial region. We see surface density variations as a function of azimuth on
the order of 10-20 %, which is roughly the size of our estimated sum of
potential systematic biases. With this work, we have demonstrated that our
method can be used to weigh distant regions of the Galactic disk despite strong
selection effects. We expect to reach even greater distances and improve our
accuracy with future Gaia data releases and further improvements to our method.Comment: 18 pages, 19 figures, accepted for publication in A&
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