Abstract
Dwarf spheroidal galaxies (dSphs) have been extensively investigated in the Local Group, but their low luminosity and surface brightness make similar work in more distant galaxy groups challenging. Modern instrumentation unlocks the possibility of scrutinizing these faint systems in other environments, expanding the parameter space of group properties. We use MUSE spectroscopy to study the properties of 14 known or suspected dSph satellites of Cen A. Twelve targets are confirmed to be group members based on their radial velocities. Two targets are background galaxies at ∼50 Mpc: KK 198 is a face-on spiral galaxy, and dw1315−45 is an ultra-diffuse galaxy with an effective radius of ∼2300 pc. The 12 confirmed dSph members of the Cen A group have old and metal-poor stellar populations and follow the stellar metallicity-luminosity relation defined by the dwarf galaxies in the Local Group. In the three brightest dwarf galaxies (KK 197, KKs 55, and KKs 58), we identify globular clusters, as well as a planetary nebula in KK 197, although its association with this galaxy and/or the extended halo of Cen A is uncertain. Using four discrete tracers, we measure the velocity dispersion and dynamical mass of KK 197. This dSph appears dark matter dominated and lies on the radial acceleration relation of star-forming galaxies within the uncertainties. It also is consistent with predictions stemming from modified Newtonian dynamics. Surprisingly, in the dwarf KK 203 we find an extended Hα ring. Careful examination of Hubble Space Telescope photometry reveals a very low level of star formation at ages between 30 and 300 Myr. The Hα emission is most likely linked to a ∼40 Myr old supernova remnant, although other possibilities for its origin cannot be entirely ruled out.
Highlights
Dwarf galaxies make up the bulk of galaxies in the Universe (Binggeli et al 1990; Ferguson & Binggeli 1994)
We discuss the overall properties of the stellar populations of the observed dwarf galaxies (Sect. 3.1)
We discovered an additional Globular clusters (GCs) in the MUSE data that is visible in the Hubble Space Telescope (HST) data as well, it can be confused with a background galaxy shining through KKs 55
Summary
Dwarf galaxies make up the bulk of galaxies in the Universe (Binggeli et al 1990; Ferguson & Binggeli 1994). The taxonomy of gas-poor dwarfs is complex (Binggeli 1994) and includes three common nomenclatures: (i) Dwarf ellipticals (dEs) have been predominantly found in galaxy clusters (Sandage & Binggeli 1984) and make up the bright end of the dwarf galaxy population from ∼109 down to ∼107 L ; (ii) dwarf spheroidals (dSphs) have traditionally been studied in the Local Group (Mateo 1998) and constitute an intermediate luminosity range from ∼107 to ∼105 L ; and (iii) ultrafaint dwarfs (UFDs) were discovered in the Local Group after the advent of the Sloan Digital Sky Survey (SDSS, York et al 2000) and other deep optical surveys and represent the faintest galaxies known, with luminosities from ∼105 to ∼103 L (e.g., Willman et al 2005; Belokurov et al 2007; Koposov et al 2015; Kim & Jerjen 2015; Mau et al 2020) All these gas-poor dwarfs, form a single sequence in structural diagrams comparing stellar luminosity, effective radius, and effective surface brightness (Tolstoy et al 2009; Kormendy et al 2009). We will explore the dynamical properties of the whole satellite system
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