From the Fire: A Deeper Look at the Phoenix Stream

TL;DR

This paper provides a detailed photometric analysis of the Phoenix stellar stream using six years of Dark Energy Survey data, revealing its structure, distance, and possible perturbations, offering insights into galactic dynamics and dark matter subhalos.

Contribution

It introduces a non-parametric modeling approach to characterize the Phoenix stream, improving measurements and identifying fluctuations and perturbations in the stream's structure.

Findings

Measured heliocentric distance as 17.4 kpc with small uncertainties.

Detected three peaks and one gap in the stream's linear intensity.

Observed fluctuations suggesting possible gravitational perturbations.

Abstract

We use six years of data from the Dark Energy Survey to perform a detailed photometric characterization of the Phoenix stellar stream, a 15-degree long, thin, dynamically cold, low-metallicity stellar system in the southern hemisphere. We use natural splines, a non-parametric modeling technique, to simultaneously fit the stream track, width, and linear density. This updated stream model allows us to improve measurements of the heliocentric distance ($17.4 \pm 0.1\,{\rm (stat.)} \pm 0.8\,{\rm (sys.)}$ kpc) and distance gradient ($-0.009 \pm 0.006$ kpc deg$^{-1}$) of Phoenix, which corresponds to a small change of $0.13 \pm 0.09$ kpc in heliocentric distance along the length of the stream. We measure linear intensity variations on degree scales, as well as deviations in the stream track on $\sim 2$-degree scales, suggesting that the stream may have been disturbed during its formation and/or evolution. We recover three peaks and one gap in linear intensity along with fluctuations in the stream track. Compared to other thin streams, the Phoenix stream shows more fluctuations and, consequently, the study of Phoenix offers a unique perspective on gravitational perturbations of stellar streams. We discuss possible sources of perturbations to Phoenix including baryonic structures in the Galaxy and dark matter subhalos.