North-South asymmetries in the Galactic thin disk associated with the vertical phase spiral as seen using LAMOST-Gaia stars
Monthly Notices of the Royal Astronomical Society(2024)
摘要
We select 1,052,469 (754,635) thin disk stars from Gaia eDR3 and LAMOST
DR7 in the range of Galactocentric radius R (guiding center radius
R_g) from 8 to 11 kpc to investigate the asymmetries between the
North and South of the disk midplane. More specifically we analyze the vertical
velocity dispersion profiles (σ_v_z(z)) in different bins of R
(R_g) and [Fe/H]. We find troughs in the profiles of
σ_v_z(z) located in both the North (z ∼ 0.7 kpc) and South (z
∼ -0.5 kpc) of the disk at all radial and chemical bins studied. The
difference between the Northern and Southern vertical velocity dispersion
profiles (Δσ_v_z(|z|)) shows a shift between curves of
different R and R_g. A similar shift exists in these NS asymmetry
profiles further divided into different [Fe/H] ranges. The sample
binned with R_g more clearly displays the features in the velocity
dispersion profiles. The shift in the peaks of the Δσ_v_z
profiles and the variation in the phase spiral shape binned by metallicity
indicate the variation of the vertical potential profiles and the radial
metallicity gradient. The wave-like signal in NS asymmetry of
σ_v_z(z) largely originates from phase spiral; while the NS
asymmetry profiles of [Fe/H] only display a weak wave-like feature near solar
radius. We perform a test particle simulation to qualitatively reproduce the
observed results. A quantitative explanation of the NS asymmetry in the
metallicity profile needs careful consideration of the spiral shape and the
perturbation model, and we leave this for future work.
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