Two New Halo Debris Streams in the Sloan Digital Sky Survey

TL;DR

This paper reports the discovery of two new stellar streams, Hermus and Hyllus, in the Sloan Digital Sky Survey data, providing insights into their properties, potential origins, and relation to known globular clusters.

Contribution

The paper introduces two previously unknown stellar streams detected in SDSS data, with detailed analysis of their properties and possible origins, expanding knowledge of galactic halo structures.

Findings

Streams are 25-50 degrees long, 15-23 kpc from Sun.

Stars are metal-poor, with [Fe/H] ~ -2.3.

Streams likely from separate progenitors, possibly linked by a common accretion event.

Abstract

Using photometry from Data Release 10 of the northern footprint of the Sloan Digital Sky Survey, we detect two new stellar streams with lengths of between $25\arcdeg$ and $50\arcdeg$. The streams, which we designate Hermus and Hyllus, are at distances of between 15 and 23 kpc from the Sun and pass primarily through Hercules and Corona Borealis. Stars in the streams appear to be metal poor, with [Fe/H] $\sim -2.3$, though we cannot rule out metallicities as high as [Fe/H] = -1.2. While Hermus passes within $1\arcdeg$ (in projection) of the globular cluster NGC 6229, a roughly one magnitude difference in distance modulus, combined with no signs of connecting with NGC 6229's Roche lobe, argue against any physical association between the two. Though the two streams almost certainly had different progenitors, similarities in preliminary orbit estimates suggest that those progenitors may themselves have been a product of a single accretion event.