A TIDALLY DISRUPTING DWARF GALAXY IN THE HALO OF NGC 253

作者：Toloba Elisa; Sand David J; Spekkens Kristine; Crnojevic Denija; Simon Joshua D; Guhathakurta Puragra; Strader Jay; Caldwell Nelson; McLeod Brian; Seth Anil C

来源：Astrophysical Journal Letters, 2016, 816(1): L5.

DOI：10.3847/2041-8205/816/1/L5

• galaxies: dwarf
• galaxies: halos
• galaxies: individual (NGC 253)
• galaxies: photometry
• galaxies: stellar content

We report the discovery of Scl-MM-Dw2, a new dwarf galaxy at a projected separation of similar to 50 kpc from NGC 253, as part of the Panoramic Imaging Survey of Centaurus and Sculptor project (PISCeS). We measure a tip of the red giant branch (RGB) distance of 3.12. +/- 0.30 Mpc, suggesting that Scl-MM-Dw2 is likely a satellite of NGC 253. We qualitatively compare the distribution of RGB stars in the color-magnitude diagram with theoretical isochrones and find that it is consistent with an old, similar to 12 Gyr, and metal-poor, -2.3 < [Fe/H]. < -1.1, stellar population. We also detect a small number of asymptotic giant branch stars consistent with a metal-poor 2-3 Gyr population in the center of the dwarf. Our non-detection of HI in a deep Green Bank Telescope spectrum implies a gas fractionM(HI)/L-V < 0.02M(circle dot) L-circle dot. The stellar and gaseous properties of Scl-MM-Dw2 suggest that it is a dwarf spheroidal galaxy. Scl-MM-Dw2 has a luminosity of M-V = -12.1 +/- 0.5 mag and a half-light radius of r(h) = 2.94 +/- 0.46 kpc, which makes it moderately larger than dwarf galaxies in the Local Group of the same luminosity. However, Scl-MM-Dw2 is very elongated (epsilon= 0.66 +/- 0.06), and it has an extremely low surface brightness (mu(0,V) = 27.7 +/- 0.6 mag arcsec(-2)). Its elongation and diffuseness make it an outlier in the ellipticity-luminosity and surface brightness-luminosity scaling relations. These properties suggest that this dwarf is being tidally disrupted by NGC 253.

• 出版日期2016-1-1