Chemodynamically Characterizing the Jhelum Stellar Stream with APOGEE-2

Abstract

We present the kinematic and chemical profiles of red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (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 ≈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-2 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 red giant branch (RGB) along the same sequence as the Jhelum stars presented by Ji et al. This new Jhelum member has [Fe/H] = −2.2 and is at the tip of the RGB. By selecting high orbital eccentricity, metal-rich stars, we identify red giants in our APOGEE2 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 α-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-2 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.