Exposing Sgr tidal debris behind the Galactic disk with M giants selected in WISE$\cap$2MASS

TL;DR

This paper demonstrates how combining WISE and 2MASS infrared data can effectively identify M giant stars to trace the Sagittarius tidal stream behind the Galactic disk, confirming model deviations and implications for dark matter.

Contribution

It introduces a new method for selecting M giants using combined infrared surveys to map the Sagittarius stream behind the Galactic disk.

Findings

Successfully identified M giants behind the Galactic disk.

Detected deviation of the Sgr trailing tail velocity from existing models.

Supported the low orbital precession hypothesis, implying less dark matter within 100 kpc.

Abstract

We show that a combination of infrared photometry from WISE and 2MASS surveys can yield highly pure samples of M giant stars. We take advantage of the new WISE$\cap$2MASS M giant selection to trace the Sagittarius trailing tail behind the Galactic disk in the direction of the anti-centre. The M giant candidates selected via broad-band photometry are confirmed spectroscopically using AAOmega on the AAT in 3 fields around the extremity of the Sgr trailing tail in the Southern Galactic hemisphere. We demonstrate that at the Sgr longitude $\tilde \Lambda_{\odot} = 204^{\circ}$, the line-of-sight velocity of the trailing tail starts to deviate from the track of the Law & Majewski (2010) model, confirming the prediction of Belokurov et al. (2014). This discovery serves to substantiate the measurement of low differential orbital precession of the Sgr stream which in turn may imply diminished dark matter content within 100 kpc.