Paper

Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey

Gruendl, R A, Jethwa, P, Tavangar, K, Carlin, J L, Monachesi, A, Balaji, P, Palmese, A, Riley, A H, R P van der Marel, Mau, S, Adamów, M, Tucker, D L, Erkal, D, Neilsen, E H, Santana-Silva, L, Li, T S, Nidever, D L, Bell, E F, Crnojević, D, Cerny, W, Ferguson, P S, Vivas, A K, Kuehn, K, Simon, J D, Bechtol, K, Olsen, K A G, Nadler, E O, Soares-Santos, M, Esteves, J, Majewski, S, McNanna, M, Zenteno, A, Johnson, L C, Martínez-Vázquez, C E, Sanchez, J, James, D J, Y -Y Mao, Morganson, E, Massana, P, Hughes, A K, Walker, A R, Pace, A B, Barkhouse, W A, Shipp, N, Sand, D J, Stringfellow, G S, Tollerud, E J, Choi, Y, Mutlu-Pakdil, B, Yanny, B, Hernandez-Lang, D, Gallart, C, DELVE Collaboration, Kuropatkin, N, Allam, S, Wechsler, R H, Paz-Chinchon, F, Pieres, A, Noël, N E D, Drlica-Wagner, A

2021

Overview

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 \\(\\tau > 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 \\(\\tau = 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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Clustering / Dwarf galaxies / Exploration / Horizontal branch stars / Magellanic clouds / Metallicity / Milky Way / Satellites / Star clusters / Stellar systems