From the Fire: Characterizing the Phoenix Stellar Stream

We use six years of data from the Dark Energy Survey (DES) to present a detailed photometric characterization of the Phoenix stream, a 15-degree long, thin, dynamically cold, low-metallicity stream 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 (17.38±0.08 kpc) and distance gradient (0.01±0.02 kpc/deg) of Phoenix. We measure linear intensity variations on degree scales, as well as wiggles in the stream track on approximately 2-degree scales, suggesting that the stream may have been disturbed during its formation and/or evolution. We recover three peaks and three gaps in linear intensity along with fluctuations in the stream track. Such small-scale fluctuations are not common in other thin streams, and the study of Phoenix offers a unique perspective on the ways that gravitational perturbations affect stellar streams. We discuss possible sources of perturbations to Phoenix including baryonic structures in the Galaxy and dark matter subhalos.