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تسجيل مستخدم جديدThe GALAH Survey: Velocity fluctuations in the Milky Way using red clump giants
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If the Galaxy is axisymmetric and in dynamical equilibrium, we expect negligible fluctuations in the residual line-of-sight velocity field. Recent results using the apg{} survey find significant fluctuations in velocity for stars in the midplane ($|z|<$0.25 kpc) out to 5 kpc, suggesting that the dynamical influence of non-axisymmetric features i.e., the Milky Ways bar, spiral arms and merger events extends out to the Solar neighborhood. Their measured power spectrum has a characteristic amplitude of 11 kms{} on a scale of 2.5 kpc. The existence of such large-scale streaming motions has important implications for determining the Suns motion about the Galactic Centre. Using Red Clump stars from glh{} and apg{}, we map the line-of-sight velocities around the Sun (d$<$5 kpc), and $|z|<$1.25 kpc from the midplane. By subtracting a smooth axisymmetric model for the velocity field, we study the residual fluctuations and compare our findings with mock survey generated by glx{}. We find negligible large-scale fluctuations away from the plane. In the mid-plane, we reproduce the earlier apg{} power spectrum but with 20% smaller amplitude (9.3 kms{}) after taking into account a few systematics (e.g., volume completeness). Using a flexible axisymmetric model the power-amplitude is further reduced to 6.3 kms{}. Additionally, our simulations show that, in the plane, distances are underestimated for high-mass Red Clump stars which can lead to spurious power-amplitude of about 5.2 kms{}. Taking this into account, we estimate the amplitude of real fluctuations to be $<$4.6 kms{}, about a factor of three less than the apg{} result.
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