Chemodynamically Characterizing the Jhelum Stellar Stream with APOGEE-2

TL;DR

This study analyzes the chemical and kinematic properties of stars in the Jhelum stellar stream using APOGEE-2 and Gaia data, revealing its likely origin from an accreted dwarf galaxy with some similarities to other stellar streams.

Contribution

It provides the first detailed chemical and orbital analysis of Jhelum stream stars, identifying new members and comparing their properties to other known structures.

Findings

One new Jhelum star identified at the tip of the red giant branch with [Fe/H]=-2.2.

Jhelum and Gaia-Enceladus-Sausage stars show similar alpha-element trends.

Orbits suggest Jhelum and GES stars do not share a common origin.

Abstract

We present the kinematic and chemical profiles of red giant stars observed by the APOGEE-2 survey in the direction of the Jhelum stellar stream, a Milky Way substructure located in the inner halo of the Milky Way at a distance from the Sun of $\approx$ 13 kpc. From the six APOGEE-2 Jhelum pointings, we isolate stars with log($g$) $<$ 3.5, leaving a sample of 289 red giant stars. From this sample of APOGEE giants, we identified seven stars that are consistent with the astrometric signal from $Gaia$ DR2 for this stream. Of these seven, one falls onto the RGB along the same sequence as the Jhelum stars presented by \cite{ji20}. This new Jhelum member has [Fe/H]=-2.2 and is at the tip of the red giant branch. By selecting high orbital eccentricity, metal-rich stars, we identify red giants in our APOGEE sample that are likely associated with the $Gaia$-Enceladus-Sausage (GES) merger. We compare the abundance profiles of the Jhelum stars and GES stars and find similar trends in $\alpha$-elements, as expected for low-metallicity populations. However, we find that the orbits for GES and Jhelum stars are not generally consistent with a shared origin. The chemical abundances for the APOGEE Jhelum star and other confirmed members of the stream are similar to stars in known stellar streams and thus are consistent with an accreted dwarf galaxy origin for the progenitor of the stream, although we cannot rule out a globular cluster origin.