Discovery of a close pair of faint dwarf galaxies in the halo of Centaurus A

D. Crnojević; D. J. Sand; N. Caldwell; P. Guhathakurta; B. McLeod; A. Seth; J. Simon; J. Strader; E. Toloba

doi:10.1088/2041-8205/795/2/L35

paper

Discovery of a close pair of faint dwarf galaxies in the halo of Centaurus A

arXiv:1409.4776 · doi:10.1088/2041-8205/795/2/L35

Abstract

As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of $\sim$ 90 kpc from the nearby elliptical galaxy NGC5128 (CenA). We measure a tip of the red giant branch distance to each dwarf, finding $D = 3.63 \pm 0.41$ Mpc for CenA-MM-Dw1 and $D = 3.60 \pm 0.41$ Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC5128. A qualitative analysis of the color magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch ( $≳ 12$ Gyr, [Fe/H] $\sim - 1.7$ to -1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities ( $M_{V} = - 10.9 \pm 0.3$ for CenA-MM-Dw1 and $- 8.4 \pm 0.6$ for CenA-MM-Dw2) and half-light radii ( $r_{h} = 1.4 \pm 0.04$ kpc for CenA-MM-Dw1 and $0.36 \pm 0.08$ kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. CenA-MM-Dw1's low central surface brightness ( $μ_{V, 0} = 27.3 \pm 0.1$ mag/arcsec $^{2}$ ) places it among the faintest and most extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a projected separation of only 3 arcmin ( $\sim 3$ kpc): we are possibly observing the first, faint satellite of a satellite in an external group of galaxies.

7 pages, 4 figures; ApJL submitted

Discovery of a close pair of faint dwarf galaxies in the halo of Centaurus A

Abstract

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