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 NGC 5128 ( 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 NGC 5128 .
A qualitative analysis of the color magnitude diagrams indicates stellar populations consisting of an old , metal-poor red giant branch ( \gtrsim 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 ( \mu _ { 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 .