The Fornax Deep Survey (FDS) with the VST

Abstract

Context. Galaxies either live in a cluster, a group, or in a field environment. In the hierarchical framework, the group environment bridges the field to the cluster environment, as field galaxies form groups before aggregating into clusters. In principle, environmental mechanisms, such as galaxy–galaxy interactions, can be more efficient in groups than in clusters due to lower velocity dispersion, which lead to changes in the properties of galaxies. This change in properties for group galaxies before entering the cluster environment is known as preprocessing. Whilst cluster and field galaxies are well studied, the extent to which galaxies become preprocessed in the group environment is unclear. Aims. We investigate the structural properties of cluster and group galaxies by studying the Fornax main cluster and the infalling Fornax A group, exploring the effects of galaxy preprocessing in this showcase example. Additionally, we compare the structural complexity of Fornax galaxies to those in the Virgo cluster and in the field. Methods. Our sample consists of 582 galaxies from the Fornax main cluster and Fornax A group. We quantified the light distributions of each galaxy based on a combination of aperture photometry, Sérsic+PSF (point spread function) and multi-component decompositions, and non-parametric measures of morphology. From these analyses, we derived the galaxy colours, structural parameters, non-parametric morphological indices (Concentration C; Asymmetry A, Clumpiness S; Gini G; second order moment of light M20), and structural complexity based on multi-component decompositions. These quantities were then compared between the Fornax main cluster and Fornax A group. The structural complexity of Fornax galaxies were also compared to those in Virgo and in the field. Results. We find significant (Kolmogorov-Smirnov test p-value < α = 0.05) differences in the distributions of quantities derived from Sérsic profiles (g′−r′, r′−i′, Re, and μ̄e,r′), and non-parametric indices (A and S) between the Fornax main cluster and Fornax A group. Fornax A group galaxies are typically bluer, smaller, brighter, and more asymmetric and clumpy. Moreover, we find significant cluster-centric trends with r′−i′, Re, and μ̄e,r′, as well as A, S, G, and M20 for galaxies in the Fornax main cluster. This implies that galaxies falling towards the centre of the Fornax main cluster become fainter, more extended, and generally smoother in their light distribution. Conversely, we do not find significant group-centric trends for Fornax A group galaxies. We find the structural complexity of galaxies (in terms of the number of components required to fit a galaxy) to increase as a function of the absolute r′-band magnitude (and stellar mass), with the largest change occurring between −14 mag ≲Mr′ ≲ −19 mag (7.5 ≲ log10(M*/M⊙) ≲ 9.7). This same trend was found in galaxy samples from the Virgo cluster and in the field, which suggests that the formation or maintenance of morphological structures (e.g., bulges, bar) are largely due to the stellar mass of the galaxies, rather than the environment they reside in.

Galaxy populations in the Hydra I cluster from the VEGAS survey I. Optical properties of a large sample of dwarf galaxies

“…• Background galaxies: Small galaxies that show features like spiral arms or bars. These properties are not likely to appear in low-mass dwarfs (Janz et al 2014;Su et al 2021), thus we conclude that they are background galaxies. We are aware that some massive dwarf galaxies can show prominent disk-like features, with star forming regions, resembling spiral galaxies (Lisker et al 2006;Michea et al 2021).…”

“…The set of the former processes is usually called mass quenching because they are all related to the mass of the galaxy. These internal mechanisms usually affect mostly massive early-type galaxies (Su et al 2021). Studies focused on isolated early-type galaxies, for which external influences can be excluded, have shown that mass quenching is effective only for galaxies more massive than 10 9 M (Geha et al 2012).…”

A tale of two tails: insights from simulations into the formation of the peculiar dwarf galaxy NGC 1427A

“…For each oriented snapshot we fed its surface brightness map to statmorph (Rodriguez-Gomez et al 2019) isolating the region of the map within 27 mag/arcsec 2 . As a reference, Su et al (2021) find an Asymmetry of 0.23 for NGC 1427A. We tried to add the Asymmetry to the constraints described in Section 4.1.…”

Brought to Light. II. Revealing the Origins of Cloaked Spiral Features in Cluster Passive Dwarf Galaxies

“…However, recent studies suggest they are not as simple as once thought. Most cluster dwarf ETGs are not well fit by a single Sérsic profile and often contain additional structures such as bars and lenses (Janz et al 2012, Su et al 2021). Nuclei are a common feature, especially in more massive dwarf ETGs (Lotz et al 2004;Côté et al 2006;Paudel et al 2010Paudel et al , 2011Neumayer et al 2020).…”