Figure 6.
Images showing
how candidate Tuc V
appears in the discovery
data (left panel) and
in the Gemini data
(right panel). Open
circles show the
position of foreground
stars. The dense core
region displayed in
the discovery image
dissolves into a series of
low-density knots in the
Gemini data, indicating
that Tuc V may not be a
coherent cluster.
like the other two candidates. We could not
confirm an overdensity that matched the
discovery detection. In Figure 6, we can see
how Tuc V looks in the discovery data (left
panel) and with the deeper Gemini data
(right panel). In the Gemini data, Tuc V dis-
solves into a series of low density knots
rather than a coherent cluster as one would
expect. So what is this intriguing object?
Tuc V has a 3D spatial distance of only 13
kpc from the Small Magellanic Cloud’s (SMC)
core. The SMC is also known to have an ex-
tended stellar halo with the SMC Northern
Overdensity (SMCNOD) residing at 8 kpc
from the SMC’s center. So at 13 kpc, Tuc V is
plausibly within the stellar halo of the SMC.
The best fit isochrone for Tuc V suggests an
11.8 Gyr stellar population with a metallic-
ity of [Fe/H] = -2.09 dex. However, the age-
metallicity degeneracy of isochrone fitting
makes an SMCNOD-type stellar population
with an age of 6 Gyr and [Fe/H] = -1.3 dex
consistent with the data. Our GMOS-S re-
sults advance the picture that Tuc V is not
a bound stellar system, but a disrupted star
cluster, merging dwarf galaxy, or a stellar
feature in the SMC halo.
standing imaging capabilities of Gemini Ob-
servatory, we are able to determine whether
a newly detected ultra-faint stellar system
belongs to the class of dwarf galaxies or star
clusters. We will continue our study of these
objects with Gemini, as each of them raises
very interesting questions on how they
formed and how they entered the Milky Way.
Our Galaxy may harbor hundreds of satellite
galaxies and clusters, most of which have
yet to be discovered and explored. Finding
and teasing apart their mysteries will drive
this field forward into the future, helping us
to better understand the substructure of our
Galaxy’s halo.
Blair Conn, a former Gemini Assistant Scientist
in Chile, is an ARC Postdoctoral Researcher at
the Australian National University. He can be
reached at: [email protected]
Helmut Jerjen is Deputy Associate Director of
Education and Graduate Program Convenor at
the Research School of Astronomy & Astrophys-
ics, Australian National University. He can be
reached at: [email protected]
As the in-depth analysis of DES 1, Eri III, and
Tuc V has demonstrated, by utilizing the out-
January 2019 / 2018 Year in Review
GeminiFocus
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