A close look at the Centaurus A group of galaxies

Abstract

Aims. We study a sample of five dwarf irregular galaxies in the CenA/M 83 group, which are companions to the giant elliptical CenA. We aim at deriving their physical properties over their lifetime and compare them to those of dwarfs located in different environments. Methods. We use archival HST/ACS data and apply synthetic color-magnitude diagram fitting in order to reconstruct the past star formation activity of the target galaxies. Results. The average star formation rate for the studied galaxies ranges from 10 −3 M yr −1 up to ∼7 × 10 −2 M yr −1 , and their mean metallicities correlate with their luminosities (from [Fe/H] ∼ −1.4 up to ∼−1.0). The form of the star formation histories varies across the sample, with quiescent periods alternating with intermittent enhancements in the star formation (from a few up to several times the average lifetime value). The dwarfs in this sample formed ∼35% to 60% of their stellar content prior to ∼5 Gyr ago. Conclusions. The resulting star formation histories for the CenA companions are similar to those found for comparable Local Group and M 81 group dwarfs. We consider this sample of dwarfs together with five previously studied M 83 dwarf irregular companions. We find no trend of the average star formation rate with tidal index or distance from the main galaxy of the group. However, dwarfs with higher baryonic masses do show higher average star formation rates, underlining the importance of intrinsic properties in governing the evolution of these galaxies. On the other hand, there is also a clear trend when looking at the recent (∼0.5−1 Gyr) level of activity. Namely, dwarfs within a denser region of the group appear to have had their star formation quenched while dwarfs located in the group outskirts show a wide range of possible star formation rates, thus indicating that external processes play a fundamental role, complementary to mass, in shaping the star formation histories of dwarf galaxies.

The dwarf galaxy satellite system of Centaurus A

“…We mock-observed these systems from random directions by placing them at a distance of 3.8 Mpc and selecting all luminous galaxies that (1) lie within a cone of opening angle 3.5 • around the host galaxy, (2) are no closer than 0.5 • to the host, and (3) have a distance of less than 800 kpc from the host, mimicking the selection volume of our observed galaxies. The V-band magnitudes M V of the selected Crnojević et al 2010Crnojević et al , 2012Crnojević et al , 2019Müller et al 2017a), and our newly confirmed members (red circles).…”

“…In Fig. 9, we present several of the scaling relations for our newly confirmed dwarf galaxies and compare them to other known Local Group (McConnachie 2012) and Centaurus A dwarf galaxies (Crnojević et al 2010(Crnojević et al , 2012(Crnojević et al , 2019Müller et al 2017a). It is apparent that the Centaurus A dwarf galaxies follow the relations as spanned by the Local Group dwarfs.…”

The Extended Halo of Centaurus A: Uncovering Satellites, Streams, and Substructures*

“…Our luminosity estimate for this object is a lower limit given its disrupting state, and thus the HI mass to light ratio is certainly even lower than the limit we derive, hinting at a genuine lack of gas for this dwarf. Previous HI studies of Cen A early-type satellites only find upper limits of M HI 7 × 10 5 M ⊙ with M HI /L B 0.25M ⊙ /L ⊙,B for this class of objects (Bouchard et al 2007), suggesting that the environment of Cen A is very effective at removing gas reservoirs in these low-mass dwarfs (see also Crnojević et al 2012).…”

Metal-poor galaxies in the local universe

“…One of the intriguing questions in this context, particularly with respect to dwarf galaxies, is the importance of a galaxy's intrinsic properties ("nature") vs. the importance of external influences ("nurture"). Clearly, both play a role in shaping dwarf galaxies in groups and clusters (e.g., [5,25,28,29,33,42,99,100,68,69,70,71,72,126,128,162]). …”