Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey. (arXiv:1912.03301v1 [astro-ph.GA])

Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey. (arXiv:1912.03301v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Mau_S/0/1/0/all/0/1">S. Mau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cerny_W/0/1/0/all/0/1">W. Cerny</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pace_A/0/1/0/all/0/1">A. B. Pace</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Choi_Y/0/1/0/all/0/1">Y. Choi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Drlica_Wagner_A/0/1/0/all/0/1">A. Drlica-Wagner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Santana_Silva_L/0/1/0/all/0/1">L. Santana-Silva</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riley_A/0/1/0/all/0/1">A. H. Riley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Erkal_D/0/1/0/all/0/1">D. Erkal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stringfellow_G/0/1/0/all/0/1">G. S. Stringfellow</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Adamow_M/0/1/0/all/0/1">M. Adamów</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carlin_J/0/1/0/all/0/1">J. L. 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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.

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