Signatures of a Tidally Induced Spiral Arm at the Anticenter of the Milky Way and a Kinematically Extended Anticenter Stream Using DESI DR2

TL;DR

This study uses DESI DR2 data to analyze the anticenter region of the Milky Way, revealing that the Monoceros Ring is likely a tidally induced spiral arm caused by the Sagittarius dwarf galaxy, and characterizing the kinematics of the Anticenter Stream.

Contribution

It provides new evidence linking the Monoceros Ring to a tidally induced spiral arm from Sgr interactions and details the kinematic properties of the Anticenter Stream using extensive spectroscopic data.

Findings

Monoceros Ring has kinematics consistent with a tidally induced spiral arm.

Sagittarius Dwarf's recent passages are dated at 0.25 and 1.10 Gyrs ago.

Anticenter Stream is kinematically decoupled from the Monoceros Ring.

Abstract

Using the Dark Energy Spectroscopic Instrument Milky Way Survey (DESI MWS), we examine the 6D space of the anticenter region of the stellar disk (150$^\circ$ $<$ Galactic longitude $<$ 220$^\circ$) using 61,883 main sequence turn-off stars. We focus on two well-known stellar overdensities in the anticenter, the Monoceros Ring (MRi) and Anticenter Stream (ACS). We find that the MRi overdensity has kinematics consistent with a tidally induced spiral arm, a type of dynamic spiral arm created by an interaction with a satellite galaxy, most likely the Sagittarius Dwarf Spheroidal galaxy (Sgr). We use the kinematics of the MRi to calculate the two most recent passage times of Sgr are 0.25 $\pm$ 0.09 Gyrs and 1.10 $\pm$ 0.23 Gyrs from the present day. We validate that the ACS is kinematically decoupled from the MRi because they are moving in opposite radial and vertical directions. We find that the kinematics associated with the ACS are not confined to our defined overdensity. The features we see in the ACS region are likely part of a broader distribution of stars with the same kinematic signature as detected in other places, like the vertical wave in the outer disk and phase spiral.