The Faint End of the Centaurus A Satellite Luminosity Function

Abstract

Abstract The Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) is constructing a wide-field map of the resolved stellar populations in the extended halos of these two nearby, prominent galaxies. We present new Magellan/Megacam imaging of a ∼3 deg2 area around Centaurus A (Cen A), which filled in much of our coverage to its south, leaving a nearly complete halo map out to a projected radius of ∼150 kpc and allowing us to identify two new resolved dwarf galaxies. We have additionally obtained deep Hubble Space Telescope (HST) optical imaging of 11 out of the 13 candidate dwarf galaxies identified around Cen A and presented in Crnojević et al. 2016a: seven are confirmed to be satellites of Cen A, while four are found to be background galaxies. We derive accurate distances, structural parameters, luminosities, and photometric metallicities for the seven candidates confirmed by our HST/ACS imaging. We further study the stellar population along the ∼60 kpc long (in projection) stream associated with Dw3, which likely had an initial brightness of M V ∼ −15 and shows evidence for a metallicity gradient along its length. Using the total sample of 11 dwarf satellites discovered by the PISCeS survey, as well as 13 brighter previously known satellites of Cen A, we present a revised galaxy luminosity function for the Cen A group down to a limiting magnitude of M V ∼ −8, which has a slope of −1.14 ± 0.17, comparable to that seen in the Local Group and in other nearby groups of galaxies.