Discovery of a New, Polar-Orbiting Debris Stream in the Milky Way Stellar Halo

TL;DR

This paper reports the discovery of a new, low-metallicity, polar-orbiting stellar debris stream in the Milky Way's halo, identified through stellar velocities and characterized by distinct metallicity and orbital properties.

Contribution

The study introduces the first identification of the Cetus Polar Stream, a previously unknown debris stream with unique metallicity and orbital features, expanding knowledge of the Milky Way's halo structure.

Findings

Discovery of the Cetus Polar Stream (CPS) in the Milky Way halo.

CPS has a metallicity of [Fe/H] = -2.1 and a nearly polar orbit.

Some CPS stars may contaminate previous Sagittarius dwarf tidal debris samples.

Abstract

We show that there is a low metallicity tidal stream that runs along l=143 deg. in the South Galactic Cap, about 34 kpc from the Sun, discovered from SEGUE stellar velocities. Since the most concentrated detections are in the Cetus constellation, and the orbital path is nearly polar, we name it the Cetus Polar Stream (CPS). Although it is spatially coincident with the Sgr dwarf trailing tidal tail at b=-70 deg., the metallicities ([Fe/H] = -2.1), ratio of blue straggler to blue horizontal branch stars, and velocities of the CPS stars differ from Sgr. Some CPS stars may contaminate previous samples of Sgr dwarf tidal debris. The unusual globular cluster NGC 5824 is located along an orbit fit to the CPS, with the correct radial velocity.