Satellite accretion in action: a tidally disrupting dwarf spheroidal around the nearby spiral galaxy NGC 253
2016
We report the discovery of NGC 253-dw2, a dwarf spheroidal (dSph) galaxy candidate undergoing tidal disruption around a nearby
spiral galaxy, NGC 253 in the
Sculptor group: the first such event identified beyond the
Local Group. The dwarf was found using small-aperture amateur telescopes, and followed up with Suprime-Cam on the 8 m
Subaru Telescopein order to resolve its brightest stars. Using g- and R_c-band photometry, we detect a
red giant branchconsistent with an old, metal-poor
stellar populationat a distance of ~ 3.5 Mpc. From the distribution of likely member stars, we infer a highly elongated shape with a
semi-major axishalf-light radius of (2 +/- 0.4) kpc.
Star countsalso yield a luminosity estimate of ~ 2x10^6 L_Sun,V (M_V ~ -10.7). The morphological properties of NGC 253-dw2 mark it as distinct from normal dSphs and imply ongoing disruption at a projected distance of ~ 50 kpc from the main galaxy. Our observations support the hierarchical paradigm wherein massive galaxies continously accrete less massive ones, and provide a new case study for dSph
infalland dissolution dynamics. We also note the continued efficacy of small telescopes for making big discoveries.
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