The Phoenix Stream: A Cold Stream in the Southern Hemisphere

Abstract

We report the discovery of a stellar stream in the Dark Energy Survey 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 τ=11.5±0.5 Gyr and [Fe/H]<−1.6, located 17.5±0.9 kpc from the Sun, gives an adequate description of the stream stellar population. The stream is detected over an extension of 8°.1 (2.5 kpc) and has a width of ∼54 pc assuming a Gaussian profile, indicating that a globular cluster (GC) is a probable progenitor. There is no known GC within 5 kpc that is compatible with being the progenitor of the stream, assuming that the stream traces its orbit. We examined overdensities (ODs) along the stream, however, no obvious counterpart-bound stellar system is visible in the coadded images. We also find ODs along the stream that appear to be symmetrically distributed-consistent with the epicyclic OD 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 OD.

Stellar Streams Discovered in the Dark Energy Survey

“…We measure a distance of 19.1 kpc ( -= m M 16.4), which is slightly larger than the value measured previously (  17.5 9 kpc). Similar to Balbinot et al (2016), we find no indication of a distance gradient.…”

“…It remains a clumpy and knotted stream, consisting of a more or less symmetric distribution of overdensities. The parameters that we derive for the Phoenix stream largely agree with those of Balbinot et al (2016). We measure a distance of 19.1 kpc ( -= m M 16.4), which is slightly larger than the value measured previously (  17.5 9 kpc).…”

“…Since the DES analysis of the Phoenix stream is discussed in great detail in Balbinot et al (2016), we offer only a brief discussion here. The Y3A2 data provide a deeper and more complete catalog with improved photometric accuracy; however, the qualitative characteristics of the Phoenix stream are predominantly unchanged.…”

Velocity Variations in the Phoenix–hermus Star Stream

“…Although Sesar et al (2015) proposed that the Phoenix stream is a recently disrupted cluster and Li et al (2016) proposed an association with a more diffuse structure in Eridanus, the attraction of the Phoenix-Hermus association is that it is a single simple system, which perhaps surprisingly accurately combines two completely independent sets of sky position and velocity data. The two stream segments are both metal-poor, [Fe/H]<−1.6 and <−1.2 for Phoenix and Hermus, respectively (Grillmair 2014;Balbinot et al 2016), helping to bolster the confidence of a single common progenitor. However, the available photometric measures are relatively low signal to noise and the moderate resolution spectra do not give highprecision velocities, so that more and better quality data will strengthen (or not) the association.…”

The outer envelopes of globular clusters. II. NGC 1851, NGC 5824 and NGC 1261*

“…They lament their lack of sufficient spatial coverage to investigate more fully the origin. Quite recently, Balbinot et al (2016) present a new discovery of a stellar stream, the Phoenix stream, in the Dark Energy Survey's first year data that lies in the direction of NGC 1261, presenting a promising connection at first. However, the authors comment that there is no clear connection between NGC 1261 and the Phoenix stream.…”