At a Crossroads: Stellar Streams in the South Galactic Cap

Abstract

We examine the distribution of old, metal-poor stars in a portion of the recently released PanSTARRs survey. We find an interesting confluence of four new cold stellar stream candidates that appear to converge on or pass near the south Galactic pole. The stream candidates, which we designate as Murrumbidgee, Molonglo, Orinoco, and Kwando, lie at a distance of ≈20 kpc and range in length from 13° to 95°, or about 5 to 33 kpc. The stream candidates are between 100 and 300 pc in width and are estimated to contain between 3000 and 8000 stars each, suggesting progenitors similar to modern day globular clusters. The trajectories of the streams imply orbits that range from hyperbolic to nearly circular. The Molonglo stream is nearly parallel to, at the same distance as, and offset by only 2.°5 from the previously discovered ATLAS stream, suggesting a possible common origin. Orinoco and Kwando also have similarly shaped, moderately eccentric, obliquely viewed orbits that suggest distinct progenitors within a common, larger parent body.