Testing kinematic distances under a realistic Galactic potential
arxiv(2024)
摘要
Obtaining reliable distance estimates to gas clouds within the Milky Way is
challenging in the absence of certain tracers. The kinematic distance approach
has been used as an alternative, derived from the assumption of circular
trajectories around the Galactic centre. Consequently, significant errors are
expected in regions where gas flow deviates from purely circular motions. We
aim to quantify the systematic errors that arise from the kinematic distance
method in the presence of a Galactic potential that is non-axisymmetric. We
investigate how these errors differ in certain regions of the Galaxy and how
they relate to the underlying dynamics. We perform 2D isothermal hydrodynamical
simulation of the gas disk with the moving-mesh code Arepo, adding the
capability of using an external potential provided by the Agama library for
galactic dynamics. We introduce a new analytic potential of the Milky Way,
taking elements from existing models and adjusting parameters to match recent
observational constraints. We find significant errors in the kinematic distance
estimate for gas close to the Sun, along sight lines towards the Galactic
centre and anti-centre, and significant deviations associated with the Galactic
bar. Kinematic distance errors are low within the spiral arms as gas resides
close to local potential minima and the resulting line-of-sight velocity is
close to what is expected for an axisymmetric potential. Interarm regions
exhibit large deviations at any given Galactic radius. This is caused by the
gas being sped up or slowed down as it travels into or out of the spiral arm.
We are able to define 'zones of avoidance' in the lv-diagram, where the
kinematic distance method is particularly unreliable and should only be used
with caution. We report a power law relation between the kinematic distance
error and the deviation of the project line-of-sight velocity from circular
motion.
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