Kinematics and Stellar Population Properties of the Andromeda Galaxy by the Spectroscopic Observations of the Guoshoujing Telescope

TL;DR

This study uses spectroscopic data from the Guoshoujing Telescope to analyze the kinematics and stellar populations of the Andromeda Galaxy, revealing its rotation, age distribution, metallicity, and dust properties.

Contribution

First spectroscopic analysis of Andromeda using GSJT data, providing detailed kinematic and stellar population properties across the galaxy.

Findings

Rotation velocities extend to about 7 kpc along the major axis.

Bulge stars are more dynamically thermal, disk stars are rotation-supported.

Bulge formed approximately 12 Gyr ago, disk is younger with some regions as young as 1 Gyr.

Abstract

The Andromeda galaxy was observed by the Guoshoujing Telescope (GSJT, formly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope -- LAMOST) during the 2009 commissioning phase. Due to the absence of standard stars for flux calibration, we use the photometric data of 15 intermediate bands in the Beijing-Arizona-Taipei-Connecticut (BATC) survey to calibrate the spectra. Total 59 spectra located in the bulge and disk of the galaxy are obtained. Kinematic and stellar population properties of the stellar content are derived with these spectra. We obtain the global velocity field and calculate corresponding rotation velocities outer to about 7 kpc along the major axis. These rotation velocity measurements complement those of the gas content, such as the H {\sc i} and CO. The radial velocity dispersion presents that the stars in the bulge are more dynamically thermal and the disk is more rotation-supported. The age distribution shows that the bulge was formed about 12 Gyr ago, the disk is relatively younger, and the ages of some regions along the spiral arms can reach as young as about 1 Gyr. These young stellar populations have relatively richer abundance and larger reddening. The overall average metallicity of the galaxy approximates the solar metallicity and a very weak abundance gradient is gained. The reddening map gives a picture of a dust-free bulge and a distinct dusty ring in the disk.