2018/04/30 by S. Khanna, Shourya Khanna, Sanjib Sharma +27 · 8 citations
Physics and Astronomy · #Amplitude #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Galactic plane #Galaxy #Gamma-ray bursts and supernovae #Milky Way #Physics #Radial velocity #Red clump #Stars #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.1093/mnras/sty2924
published in Monthly Notices of the Royal Astronomical Society 482(3), 4215-4232 (Oxford University Press) · 20 pages, 16 figures, accepted for publication in MNRAS
openalex publication_date 2018/10/29 · arxiv created 2018/11/03 · arxiv updated 2018/11/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 APOGEE survey find significant fluctuations in velocity for stars in the mid-plane (||z|| <0.25 kpc) out to 5 kpc, suggesting that the dynamical influence of non-axisymmetric features, i.e. the Milky Way’s bar, spiral arms, and merger events extends out to the Solar neighbourhood. Their measured power spectrum has a characteristic amplitude of 11 km s−1 on a scale of 2.5 kpc. The existence of such large-scale streaming motions has important implications for determining the Sun’s motion about the Galactic Centre. Using Red Clump stars from GALAH and APOGEE, we map the line-of-sight velocities around the Sun (d < 5 kpc), and ||z|| <1.25 kpc from the mid-plane. By subtracting a smooth axisymmetric model for the velocity field, we study the residual fluctuations and compare our findings with mock survey generated by galaxia. We find negligible large-scale fluctuations away from the plane. In the mid-plane, we reproduce the earlier APOGEE power spectrum but with 20 per cent smaller amplitude (9.3 km s−1) 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 km s−1. 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 km s−1. Taking this into account, we estimate the amplitude of real fluctuations to be <4.6 km s−1, about a factor of three less than the APOGEE result.