2023/04/25 by Guozhen Hu, Zhengyi Shao, Hu, Guozhen +3
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2304.12929
openalex publication_date 2023/04/25 · openalex created_date 2023/04/27 · openalex updated_date 2026/07/28
We investigate the angular momentum of mono-abundance populations (MAPs) of the Milky Way thick disk by using a sample of 26,076 giant stars taken from APOGEE DR17 and Gaia EDR3. The vertical and perpendicular angular momentum components, LZ and LP, of MAPs in narrow bins have significant variations across the [α/M]-[M/H] plane. LZ and LP systematically change with [M/H] and [α/M] and can be alternatively quantified by the chemical gradients: d[\rm M/H]/dLZ = 1.2× 10-3 dex kpc-1 km-1 s, d\rm [M/H]/dLP = -5.0× 10-3 dec kpc-1 km-1 s, and d[α/\rm M]/dLZ = -3.0× 10-4 dex kpc-1 km-1 s, d[α/\rm M]/dLP = 1.2× 10-3 dec kpc-1 km-1 s. These correlations can also be explained as the chemical-dependence of the spatial distribution shape of MAPs. We also exhibit the corresponding age dependence of angular momentum components. Under the assumption that the guiding radius (Rg) is proportional to LZ, it provides direct observational evidence of the inside-out structure formation scenario of the thick disk, with dRg/dAge = -1.9 kpc Gyr-1. The progressive changes in the disk thickness can be explained by the upside-down formation or/and the consequent kinematical heating.