2020ApJ...890..136M

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of D_☉=116.3_–0.6^+0.6kpc, a half-light radius of r_h=2.3_–0.3^+0.4arcmin, an age of τ> 12.85Gyr, a metallicity of Z=0.0002_–0.0002^+0.0001, and an absolute magnitude of M_V=-5.55_–0.11^+0.11mag. This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of D_☉=19.0_–0.6^+0.5kpc, a half-light radius of r_h=0.97_–0.17^+0.24arcmin, an age of τ=12.5_–0.7^+1.0Gyr, a metallicity of Z=0.0005_–0.0001^+0.0002, and an absolute magnitude of M_V=-0.2_–0.6^+0.8mag, consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.