Phlegethon, a nearby $75\deg$-long retrograde stellar stream

TL;DR

The paper reports the discovery of a 75-degree long, nearby, retrograde stellar stream in Gaia DR2, demonstrating the effectiveness of the STREAMFINDER algorithm in detecting ultra-faint, extended structures that can probe the Galactic potential.

Contribution

This work introduces the discovery of Phlegethon, a nearby, ultra-faint stellar stream, using a new detection algorithm, highlighting its potential for Galactic studies.

Findings

Stream is 75 degrees long and 3.8 kpc from the Sun.

Stream has a low surface brightness of ~34.3 mag/arcsec^2.

Stream's mass is approximately 2580 solar masses.

Abstract

We report the discovery of a $75\deg$ long stellar stream in Gaia DR2 catalog, found using the new STREAMFINDER algorithm. The structure is probably the remnant of a now fully disrupted globular cluster, lies $\approx 3.8 \, {\rm kpc}$ away from the Sun in the direction of the Galactic bulge, and possesses highly retrograde motion. We find that the system orbits close to the Galactic plane at Galactocentric distances between $4.9$ and $19.8 \, {\rm kpc}$. The discovery of this extended and extremely low surface brightness stream ($\Sigma_G\sim 34.3 \, {\rm mag \, arcsec^{-2}}$) with a mass of only $2580\pm140 \, {\rm\,M_\odot}$, demonstrates the power of the STREAMFINDER algorithm to detect even very nearby and ultra-faint structures. Due to its proximity and length we expect that Phlegethon will be a very useful probe of the Galactic acceleration field.