The Faint End of the Centaurus A Satellite Luminosity Function

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 deg 2 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 eleven out of the thirteen candidate dwarf galaxies identified around Cen A and presented in Crnojević et al. (2016b): 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 eleven dwarf satellites discovered by the PISCeS survey, as well as thirteen 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.

Wide-field Survey of Dwarf Satellite Systems around 10 Hosts in the Local Volume

“…Carlsten et al (2019a) applied this to the catalog of candidate satellites of M101 of Bennet et al (2017) and was able to show that the majority were background contaminants while confirming two as actual companions. The results of Carlsten et al (2019a) have since been confirmed by Bennet et al (2019) using considerable HST follow-up.…”

The Satellite Luminosity Function of M101 into the Ultra-faint Dwarf Galaxy Regime

“…We consider the M101 luminosity function to be 90% complete down to MV ≈−7.7 mag, and 50% complete down to MV ≈−7.4 mag (hollow symbol; we also mark the magnitude range between these two values with a dashed line); see Section 4 for details. The data for the other luminosity functons come from Smercina et al (2018) for M94, Crnojević et al (2019) for Cen A, Chiboucas et al (2013) and Smercina et al (2017) for M81, Martin et al (2016) & McConnachie et al (2018 for M31 and McConnachie (2012) for the MW. Note that this is a lower limit for the MW due to incomplete spatial coverage; no attempt was made to correct any luminosity function for incompleteness.…”

“…Note that this is a lower limit for the MW due to incomplete spatial coverage; no attempt was made to correct any luminosity function for incompleteness. We denote the region where the Cen A and M81 luminosity functions become incomplete with hollow symbols and dashed lines, as reported by Crnojević et al (2019) and Chiboucas et al (2013), respectively. Galaxies are listed in descending order of stellar mass.…”

“…There is good agreement between both datasets, although the HST-derived magnitude uncertainties tend to be slightly larger. Previous studies (Merritt et al 2016;Bennet et al 2017;Crnojević et al 2019) have shown that the smaller primary mirror on HST is less effective at detecting the diffuse low surface brightness outer regions of unresolved targets. In addition, the small pixel scale of HST means that it is not optimised for unresolved LSB candidates.…”

The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

“…A number of studies carrying out deep satellite searches around Milky Way analogues in the Local Volume are currenly underway (Smercina et al 2018;Crnojević et al 2019;Bennet et al 2019;Carlsten et al 2019). This should significantly increase the number of systems with well-resolved satellite populations which will allow for higher-precision measurements of satellite radial distributions and the variation in satellite luminosity function amplitudes (Bennet et al 2019).…”