On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus III and Tucana V

Blair C. Conn; Helmut Jerjen; Dongwon Kim; Mischa Schirmer

doi:10.3847/1538-4357/aa9eda

paper

On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus III and Tucana V

arXiv:1712.01439 · doi:10.3847/1538-4357/aa9eda

Abstract

We use deep Gemini/GMOS-S $g, r$ photometry to study the three ultra-faint dwarf galaxy candidates DES1, Eridanus III (Eri III) and Tucana V (Tuc V). Their total luminosities, $M_{V}$ (DES1) $= - 1.42 \pm 0.50$ and $M_{V}$ (Eri III) $= - 2.07 \pm 0.50$ , and mean metallicities, [Fe/H] $= - 2.3 8_{- 0.19}^{+ 0.21}$ and [Fe/H] $= - 2.4 0_{- 0.12}^{+ 0.19}$ , are consistent with them being ultra-faint dwarf galaxies as they fall just outside the 1-sigma confidence band of the luminosity-metallicity relation for Milky Way satellite galaxies. However, their positions in the size-luminosity relation suggests that they are star clusters. Interestingly, DES1 and Eri III are at relatively large Galactocentric distances with DES1 located at $D_{GC} = 74 \pm$ 4 kpc and Eri III at $D_{GC} = 91 \pm$ 4 kpc. In projection both objects are in the tail of gaseous filaments trailing the Magellanic Clouds and have similar 3D-separations from the Small Magellanic Cloud (SMC): $Δ D_{S M C, D E S 1}$ = 31.7 kpc and $Δ D_{S M C, E r i I I I}$ = 41.0 kpc, respectively. It is plausible that these stellar systems are metal-poor SMC satellites. Tuc V represents an interesting phenomenon in its own right. Our deep photometry at the nominal position of Tuc V reveals a low-level excess of stars at various locations across the GMOS field without a well-defined centre. A SMC Northern Overdensity-like isochrone would be an adequate match to the Tuc V colour-magnitude diagram, and the proximity to the SMC ( $12. 1^{\circ}$ ; $Δ D_{S M C, T u c V} = 13$ kpc) suggests that Tuc V is either a chance grouping of stars related to the SMC halo or a star cluster in an advanced stage of dissolution.

arXiv comment23 Pages, 26 Figures, Accepted for publication in ApJ

On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus III and Tucana V

Abstract

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