GeminiFocus April 2018 | Page 9

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 . 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 dissolves 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 extended 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 metallicity of [ Fe / H ] = -2.09 dex . However , the agemetallicity 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 results 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 .
As the in-depth analysis of DES 1 , Eri III , and Tuc V has demonstrated , by utilizing the outstanding imaging capabilities of Gemini Observatory , 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 : blair . conn @ anu . edu . au
Helmut Jerjen is Deputy Associate Director of Education and Graduate Program Convenor at the Research School of Astronomy & Astrophysics , Australian National University . He can be reached at : helmut . jerjen @ anu . edu . au
April 2018 GeminiFocus