Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
Creators: name: Mau, S.
name: Cerny, W.
name: Pace, A. B.
name: Choi, Y.
name: Drlica-Wagner, A.
name: Santana-Silva, L.
name: Riley, A. H.
name: Erkal, D.
name: Stringfellow, G. S.
name: Adamów, M.
name: Carlin, J. L.
name: Gruendl, R. A.
name: Hernandez-Lang, D.
name: Kuropatkin, N.
name: Li, T. S.
name: Martínez-Vázquez, C. E.
name: Morganson, E.
name: Mutlu-Pakdil, B.
name: Neilsen, E. H.
name: Nidever, D. L.
name: Olsen, K. A. G.
name: Sand, D. J.
name: Tollerud, E. J.
name: Tucker, D. L.
name: Yanny, B.
name: Zenteno, A.
name: Allam, S.
name: Barkhouse, W. A.
name: Bechtol, K.
name: Bell, E. F.
name: Balaji, P.
name: Crnojević, D.
name: Esteves, J.
name: Ferguson, P. S.
name: Gallart, C.
name: Hughes, A. K.
name: James, D. J.
name: Jethwa, P.
name: Johnson, L. C.
name: Kuehn, K.
name: Majewski, S.
name: Mao, Y. -Y.
name: Massana, P.
name: McNanna, M.
name: Monachesi, A.
name: Nadler, E. O.
name: Noël, N. E. D.
name: Palmese, A.
name: Paz-Chinchon, F.
name: Pieres, A.
name: Sanchez, J.
name: Shipp, N.
name: Simon, J. D.
name: Soares-Santos, M.
name: Tavangar, K.
name: van der Marel, R. P.
name: Vivas, A. K.
name: Walker, A. R.
name: Wechsler, R. H.
Publisher: name: arXiv
Year: 2019
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 ${\rm D}_{\odot} = 116.3_{-0.6}^{+0.6}$ kpc, a half-light radius of $r_h = 2.3_{-0.3}^{+0.4}$ arcmin, an age of $τ&gt; 12.85$ Gyr, a metallicity of $Z = 0.0002_{-0.0002}^{+0.0001}$, and an absolute magnitude of $M_V = -5.55_{-0.11}^{+0.11}$ mag. 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 ${\rm D}_{\odot} = 19.0_{-0.6}^{+0.5} kpc$, a half-light radius of $r_h = 0.97_{-0.17}^{+0.24}$ arcmin, an age of $τ= 12.5_{-0.7}^{+1.0}$ Gyr, a metallicity of $Z = 0.0005_{-0.0001}^{+0.0002}$, and an absolute magnitude of $M_V = -0.2_{-0.6}^{+0.8}$ mag, 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.
description: 17 pages, 6 figures, 1 table; updated to match published version; updated to address erratum