Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey

We summarize the recent discovery of an ultra-faint stellar system found near the Magellanic Clouds in data from the DECam Local Volume Exploration (DELVE) Survey. This new system, DELVE J0155−6815 (DELVE 2), is located at a heliocentric distance of 71±4 kpc, placing it at a 3D physical separation of 12 kpc from the center of Small Magellanic Cloud (SMC) and 28 kpc from the center of the Large Magellanic Cloud (LMC). DELVE 2 is identified as a resolved overdensity of old (age > 13.3 Gyr) and metal-poor ([Fe/H]=−2.0 dex) stars. We measure the system’s projected half-light radius and absolute magnitude as r_1/2 = 21 ± 4 pc and M_V =−2.1 ± 0.5 mag; this size and luminosity places the system in the ambiguous regime between the population of recently discovered ultra-faint globular clusters and the smallest ultra-faint dwarf galaxies. DELVE 2 is detected in Gaia DR2 with a clear proper motion signal, with multiple blue horizontal branch stars near the centroid of the system with proper motions consistent with the systemic mean. By comparing the spatial position and proper motion of DELVE 2 with simulations of the accreted satellite population of the LMC, we find that the system is very likely to be associated with the LMC.