The properties of red giant stars along the Sagittarius tidal tails ^⋆

¹ Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, 264209 Weihai, PR China
e-mail: swb@sdu.edu.cn
² Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, PR China
³ Research School of Astronomy and Astrophysics, The Australian National University, Weston Creek, ACT 2611, Australia
⁴ University of Chinese Academy of Sciences 19A Yuquan Rd, Shijingshan District, 100049 Beijing, PR China
⁵ Physics and Geosciences, Angelo State University, San Angelo, TX 76904, USA
⁶ Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, 210042 Nanjing, PR China

Received: 3 June 2016
Accepted: 30 September 2016

Abstract

Aims. We aim to measure the metallicity distribution and velocity distribution of red giant branch (RGB) stars along the Sagittarius dwarf galaxy (Sgr) streams. Thanks to the large number of stars of the Sloan Digital Sky Survey (SDSS) sample, we can study the properties of streams as a function of the Λ_⊙ from the Sgr core.

Methods. Using the ~22 000 RGB stars from the ninth data release of SDSS, we selected 1100 RGB stars belonging to the streams of the Sgr. As compared with red horizontal branch stars (Shi et al. 2012, ApJ, 751, 130) the RGB stars constitute a large sample size and extend to a metal-poor component of [Fe/H] ~−3.0 dex. In particular, this RGB sample has a significant number of stars in the second wrap of the leading stream of the Sgr (leading arm 2), and thus provides a good opportunity to understand the properties of the leading stream.

Results. We derive a metallicity gradient of −(2.3 ± 0.5) × 10^-3 dex deg^-1 in leading arm 2 for the first time, of −(1.6 ± 0.4) × 10^-6 dex deg^-1 for the leading arm 1, and of −(1.3 ± 0.3) × 10^-3 dex deg^-1 for the trailing arm 1. We check the distribution of Sgr stars in phase space and find a velocity dispersion of ~21.5 km s^-1 for leading arm 1. Finally, we identify a possible new branch in leading arm 1.