The Phoenix stream: a cold stream in the Southern hemisphere

TL;DR

The paper reports the discovery and characterization of the Phoenix stellar stream in DES Year 1 data, revealing a cold, old, metal-poor stream likely originating from a globular cluster, with detailed analysis of its properties and potential progenitors.

Contribution

This work presents the first detection and detailed analysis of the Phoenix stream, including its stellar population, extent, width, and possible progenitor, expanding knowledge of stellar streams in the Southern hemisphere.

Findings

Phoenix stream is 8.1° long and ~54 pc wide.

Stellar population is approximately 11.5 Gyr old with [Fe/H] < -1.6.

No known globular cluster is identified as the progenitor.

Abstract

We report the discovery of a stellar stream in the Dark Energy Survey (DES) Year 1 (Y1A1) data. The discovery was made through simple color-magnitude filters and visual inspection of the Y1A1 data. We refer to this new object as the Phoenix stream, after its resident constellation. After subtraction of the background stellar population we detect a clear signal of a simple stellar population. By fitting the ridge line of the stream in color-magnitude space, we find that a stellar population with age $\tau=11.5\pm0.5$ Gyr and $[Fe/H]<-1.6$ located 17.5$\pm$0.9 kpc from the Sun gives an adequate description of the stream stellar population. The stream is detected over an extension of 8$^{\circ}.$1 (2.5 kpc) and has a width of $\sim$54 pc assuming a Gaussian profile, indicating that a globular cluster is a probable progenitor. There is no known globular cluster within 5 kpc compatible with being the progenitor of the stream, assuming that the stream traces its orbit. We examined overdensities along the stream, however no obvious counterpart bound stellar system is visible in the coadded images. We also find overdensities along the stream that appear to be symmetrically distributed - consistent with the epicyclic overdensity scenario for the formation of cold streams - as well as a misalignment between the Northern and Southern part of stream. Despite the close proximity we find no evidence that this stream and the halo cluster NGC 1261 have a common accretion origin linked to the recently found EriPhe overdensity (Li et al. 2016).