A Deeper Look at DES Dwarf Galaxy Candidates: Grus I and Indus II. (arXiv:2005.06478v1 [astro-ph.GA])

A Deeper Look at DES Dwarf Galaxy Candidates: Grus I and Indus II. (arXiv:2005.06478v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Cantu_S/0/1/0/all/0/1">Sarah A. Cantu</a> (1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Pace_A/0/1/0/all/0/1">Andrew B. Pace</a> (3 and 1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Marshall_J/0/1/0/all/0/1">Jennifer Marshall</a> (1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Strigari_L/0/1/0/all/0/1">Louis E. Strigari</a> (1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Crnojevic_D/0/1/0/all/0/1">Denija Crnojevic</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Simon_J/0/1/0/all/0/1">Joshua D. Simon</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Drlica_Wagner_A/0/1/0/all/0/1">A. Drlica-Wagner</a> (6 and 7 and 8), <a href="http://arxiv.org/find/astro-ph/1/au:+Bechtol_K/0/1/0/all/0/1">K. Bechtol</a> (9 and 10), <a href="http://arxiv.org/find/astro-ph/1/au:+Martinez_Vazquez_C/0/1/0/all/0/1">Clara E. Martínez-Vázquez</a> (11), <a href="http://arxiv.org/find/astro-ph/1/au:+Santiago_B/0/1/0/all/0/1">B. Santiago</a> (12 and 13), <a href="http://arxiv.org/find/astro-ph/1/au:+Amara_A/0/1/0/all/0/1">A. Amara</a> (14), <a href="http://arxiv.org/find/astro-ph/1/au:+Stringer_K/0/1/0/all/0/1">K. M. Stringer</a> (1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Diehl_H/0/1/0/all/0/1">H. T. Diehl</a> (15), The <a href="http://arxiv.org/find/astro-ph/1/au:+Collaboration_DES/0/1/0/all/0/1">DES Collaboration</a> ((1) George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy Texas A&M University, (2) Department of Physics & Astronomy Texas A&M University, (3) McWilliams Center for Cosmology Carnegie Mellon University (4) Department of Chemistry and Physics University of Tampa, (5) Observatories of the Carnegie Institution for Science, (6) Fermi National Accelerator Laboratory, (7) Kavli Institute for Cosmological Physics, (8) Department of Astronomy and Astrophysics University of Chicago, (9) Physics Department 2320 Chamberlin Hall University of Wisconsin-Madison, (10) LSST, (11) Cerro Tololo Inter-American Observatory NSF's National Optical-Infrared Astronomy Research Laboratory, (12) Instituto de Física UFRGS, (13) Laboratório Interinstitucional de e-Astronomia – LIneA, (14) Department of Physics ETH Zurich, (15) Fermi National Accelerator Laboratory)

We present deep $g$- and $r$-band Magellan/Megacam photometry of two dwarf
galaxy candidates discovered in the Dark Energy Survey (DES), Grus I and Indus
II (DES J2038-4609). For the case of Grus I, we resolved the main sequence
turn-off (MSTO) and $sim 2$ mags below it. The MSTO can be seen at $g_0sim
24$ with a photometric uncertainty of $0.03$ mag. We show Grus I to be
consistent with an old, metal-poor ($sim 13.3$ Gyr, [Fe/H]$sim-1.9$) dwarf
galaxy. We derive updated distance and structural parameters for Grus I using
this deep, uniform, wide-field data set. We find an azimuthally averaged
half-light radius more than two times larger ($sim 151^{+21}_{-31}$ pc; $sim
4.^{prime} 16^{+0.54}_{-0.74}$) and an absolute $V$-band magnitude $sim-4.1$
that is $sim 1$ magnitude brighter than previous studies. We obtain updated
distance, ellipticity, and centroid parameters which are in agreement with
other studies within uncertainties. Although our photometry of Indus II is
$sim 2-3$ magnitudes deeper than the DES Y1 Public release, we find no
coherent stellar population at its reported location. The original detection
was located in an incomplete region of sky in the DES Y2Q1 data set and was
flagged due to potential blue horizontal branch member stars. The best fit
isochrone parameters are physically inconsistent with both dwarf galaxies and
globular clusters. We conclude that Indus II is likely a false-positive,
flagged due to a chance alignment of stars along the line of sight.

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