426 research outputs found
M2M modelling of the Galactic disc via PRIMAL: Fitting to Gaia Error Added Data
We have adapted our made-to-measure (M2M) algorithm PRIMAL to use mock Milky
Way like data constructed from an N-body barred galaxy with a boxy bulge in a
known dark matter potential. We use M0 giant stars as tracers, with the
expected error of the ESA space astrometry mission Gaia. We demonstrate the
process of constructing mock Gaia data from an N-body model, including the
conversion of a galactocentric Cartesian coordinate N-body model into
equatorial coordinates and how to add error to it for a single stellar type. We
then describe the modifications made to PRIMAL to work with observational
error. This paper demonstrates that PRIMAL can recover the radial profiles of
the surface density, radial velocity dispersion, vertical velocity dispersion
and mean rotational velocity of the target disc, along with the pattern speed
of the bar, to a reasonable degree of accuracy despite the lack of accurate
target data. We also construct mock data which take into account dust
extinction and show that PRIMAL recovers the structure and kinematics of the
disc reasonably well. In other words, the expected accuracy of the Gaia data is
good enough for PRIMAL to recover these global properties of the disc, at least
in a simplified condition, as used in this paper.Comment: 16 pages, 10 figures, submitted to MNRAS 17th Dec 2013, accepted 30th
June 201
Gas and Stellar Motions and Observational Signatures of Co-Rotating Spiral Arms
We have observed a snapshot of our N-body/Smoothed Particle Hydrodynamics
simulation of a Milky Way-sized barred spiral galaxy in a similar way to how we
can observe the Milky Way. The simulated galaxy shows a co-rotating spiral arm,
i.e. the spiral arm rotates with the same speed as the circular speed. We
observed the rotation and radial velocities of the gas and stars as a function
of the distance from our assumed location of the observer at the three lines of
sight on the disc plane, (l, b) = (90, 0), (120, 0) and (150,0) deg. We find
that the stars tend to rotate slower (faster) behind (at the front of) the
spiral arm and move outward (inward), because of the radial migration. However,
because of their epicycle motion, we see a variation of rotation and radial
velocities around the spiral arm. On the other hand, the cold gas component
shows a clearer trend of rotating slower (faster) and moving outward (inward)
behind (at the front of) the spiral arm, because of the radial migration. We
have compared the results with the velocity of the maser sources from Reid et
al. (2014), and find that the observational data show a similar trend in the
rotation velocity around the expected position of the spiral arm at l = 120
deg. We also compared the distribution of the radial velocity from the local
standard of the rest, V_LSR, with the APOGEE data at l = 90 deg as an example.Comment: 10 pages, 7 figures, accepted for publication in MNRA
The stellar kinematics of co-rotating spiral arms in Gaia mock observations
We have observed an N-body/Smoothed Particle Hydrodynamics simulation of a
Milky Way like barred spiral galaxy. We present a simple method that samples
N-body model particles into mock Gaia stellar observations and takes into
account stellar populations, dust extinction and Gaia's science performance
estimates. We examine the kinematics around a nearby spiral arm at a similar
position to the Perseus arm at three lines of sight in the disc plane;
(l,b)=(90,0), (120,0) and (150,0) degrees. We find that the structure of the
peculiar kinematics around the co-rotating spiral arm, which is found in Kawata
et al. (2014b), is still visible in the observational data expected to be
produced by Gaia despite the dust extinction and expected observational errors
of Gaia. These observable kinematic signatures will enable testing whether the
Perseus arm of the Milky Way is similar to the co-rotating spiral arms commonly
seen in N-body simulations.Comment: 9 pages 4 Figures, submitted to MNRAS 22nd Dec 201
Made-to-Measure Modelling of Globular Clusters
We present the first application of the made-to-measure method for modelling
dynamical systems to globular clusters. Through the made-to-measure algorithm,
the masses of individual particles within a model cluster are adjusted while
the system evolves forward in time via a gravitational -body code until the
model cluster is able to reproduce select properties of an observed cluster.
The method is first applied to observations of mock isotropic and anisotropic
clusters while fitting against the cluster's three dimensional or projected
density profile, density weighted mean-squared velocity profile, or its density
profile with individual mean-squared velocity profiles. We find that a
cluster's three-dimensional density profile can easily be reproduced by the
made-to-measure method, with minor discrepancies in the outer regions if
fitting against a cluster's projected surface density or projected kinematic
properties. If an observed cluster is anisotropic, only fitting against the
cluster's density profile and individual mean-squared velocity profiles will
fully recover the full degree of anisotropy. Partial anisotropy can be
recovered as long as two kinematic properties are included in the fit. We
further apply the method to observations of the Galactic globular cluster M4
and generate a complete six-dimensional representation of the cluster that
reproduces observations of its surface density profile, mean-squared proper
motion velocity profile, and mean-squared line of sight velocity profile. The
M2M method predicts M4 is primarily isotropic with a mass of and a half-mass radius of pc.Comment: 11 pages, 10 figures, submitted to MNRAS for publicatio
- …