1,145 research outputs found
Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations
We investigate the kinematic signatures induced by spiral and bar structure
in a set of simulations of Milky Way-sized spiral disc galaxies. The set
includes test particle simulations that follow a quasi-stationary density
wave-like scenario with rigidly rotating spiral arms, and -body simulations
that host a bar and transient, co-rotating spiral arms. From a location similar
to that of the Sun, we calculate the radial, tangential and line-of-sight
peculiar velocity fields of a patch of the disc and quantify the fluctuations
by computing the power spectrum from a two-dimensional Fourier transform. We
find that the peculiar velocity power spectrum of the simulation with a bar and
transient, co-rotating spiral arms fits very well to that of APOGEE red clump
star data, while the quasi-stationary density wave spiral model without a bar
does not. We determine that the power spectrum is sensitive to the number of
spiral arms, spiral arm pitch angle and position with respect to the spiral
arm. However, it is necessary to go beyond the line of sight velocity field in
order to distinguish fully between the various spiral models with this method.
We compute the power spectrum for different regions of the spiral discs, and
discuss the application of this analysis technique to external galaxies.Comment: 14 pages, 11 figures. Improved and MNRAS Accepte
The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc
<~ R <~ 14 kpc from the first year of data from the Apache Point Observatory
Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities
of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg
out to distances of 10 kpc using an axisymmetric kinematical model that
includes a correction for the asymmetric drift of the warm tracer population
(\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to
be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately
flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also
measure the Sun's position and velocity in the Galactocentric rest frame,
finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial
velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{\phi,sun} =
242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's
radial velocity and with the observed proper motion of Sgr A*. We investigate
various systematic uncertainties and find that these are limited to offsets at
the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that
we consider, we find that V_c(R_0) 99% confidence. We find an
offset between the Sun's rotational velocity and the local circular velocity of
26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12
km/s. This larger offset reconciles our value for V_c with recent claims that
V_c >~ 240 km/s. Combining our results with other data, we find that the Milky
Way's dark-halo mass within the virial radius is ~8x10^{11} M_sun.Comment: submitted to Ap
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