Another Look at the EBS: A Stellar Debris Stream and a Possible Progenitor

TL;DR

This paper reexamines the Eastern Banded Structure (EBS) stellar stream using SDSS data, identifying a potential progenitor, Hydra I, and discussing its orbit, origin, and dynamical history.

Contribution

It provides new analysis of the EBS stream, identifies Hydra I as a likely progenitor remnant, and suggests the progenitor was probably a globular cluster based on dynamical evidence.

Findings

EBS is an 18-degree-long stellar stream with a distinct orbit.

Hydra I is a prominent concentration likely representing the progenitor.

The progenitor was probably a globular cluster that experienced significant dynamical heating.

Abstract

Using the Sloan Digital Sky Survey Data Release 7, we reexamine the Eastern Banded Structure (EBS), a stellar debris stream first discovered in Data Release 5 and more recently detected in velocity space by Schlaufman et al. The visible portion of the stream is 18 degrees long, lying roughly in the Galactic Anticenter direction and extending from Hydra to Cancer. At an estimated distance of 9.7 kpc, the stream is approximately 170 pc across on the sky. The curvature of the stream implies a fairly eccentric box orbit that passes close to both the Galactic center and to the sun, making it dynamically distinct from the nearby Monoceros, Anticenter, and GD-1 streams. Within the stream is a relatively strong, 2 degree-wide concentration of stars with a very similar color-magnitude distribution that we designate Hydra I. Given its prominence within the stream and its unusual morphology, we suggest that Hydra I is the last vestige of the EBS's progenitor, possibly already unbound or in the final throes of tidal dissolution. Though both Hydra I and the EBS have a relatively high velocity dispersion, given the comparatively narrow width of the stream and the high frequency of encounters with the bulge and massive constituents of the disk that such an eccentric orbit would entail, we suggest that the progenitor was likely a globular cluster, and that both it and the stream have undergone significant heating over time.