The Fornax Deep Survey with VST. X. The assembly history of the bright galaxies and intra-group light in the Fornax A subgroup

Raj, M. A.; Iodice, E.; Napolitano, N. R.; Hilker, M.; Spavone, M.; Peletier, R. F.; Su, H. -S.; Falcón-Barroso, J.; van de Ven, G.; Cantiello, M.; Kleiner, D.; Venhola, A.; Mieske, S.; Paolillo, M.; Capaccioli, M.; Schipani, P.
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Astronomy and Astrophysics

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Context. We present the study of the south-west group in the Fornax cluster centred on the brightest group galaxy (BGG) Fornax A, which was observed as part of the Fornax Deep Survey (FDS). This includes the analysis of the bright group members (mB < 16 mag) and the intra-group light (IGL).
Aims: The main objective of this work is to investigate the assembly history of the Fornax A group and to compare its physical quantities as a function of the environment to that of the Fornax cluster core.
Methods: For all galaxies, we extracted the azimuthally averaged surface brightness profiles in three optical bands (g, r, i) by modelling the galaxy's isophotes. We derived their colour (g - i) profiles, total magnitude, effective radius in all respective bands, stellar mass, and the break radius in the r-band. The long integration time and large covered area of the FDS allowed us to also estimate the amount of IGL.
Results: The majority of galaxies in the Fornax A group are late-type galaxies (LTGs), spanning a range of stellar mass of 8 < log(M* M☉) < 10.5. Six out of nine LTGs show a Type III (up-bending) break in their light profiles, which is either suggestive of strangulation halting star formation in their outskirts or their H I-richness causing enhanced star formation in their outer-discs. Overall, we do not find any correlations between their physical properties and their group-centric distance. The estimated luminosity of the IGL is 6 ± 2 × 1010 L☉ in the g-band, which corresponds to about 16% of the total light in the group.
Conclusions: The Fornax A group appears to be in an early-stage of assembly with respect to the cluster core. The environment of the Fornax A group is not as dense as that of the cluster core, with all galaxies except the BGG showing similar morphology, comparable colours and stellar masses, and Type III disc-breaks, without any clear trend in these properties with group-centric distances. The low amount of IGL is also consistent with this picture, since there were no significant gravitational interactions between galaxies that modified the galaxies' structure and contributed to the build-up of the IGL. The main contribution to the IGL is from the minor merging in the outskirts of the BGG NGC 1316 and, probably, the disrupted dwarf galaxies close to the group centre.
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