Astronomy & Astrophysics manuscript no. Fornax_A_LTGs_AA c ESO 2020 September 4, 2020 The Fornax Deep Survey with VST X. The assembly history of the bright galaxies and intra-group light in the Fornax A subgroup M. A. Raj1; 2; 3, E. Iodice1; 3, N. R. Napolitano4, M. Hilker3, M. Spavone1, R. F. Peletier5, H-S. Su6, J. Falcón-Barroso7; 8, G. van de Ven9, M. Cantiello10, D. Kleiner11, A. Venhola6, S. Mieske12, M. Paolillo2; 13; 1, M. Capaccioli2, and P. Schipani1 1 INAF-Astronomical observatory of Capodimonte, via Moiariello 16, Naples, I-80131, Italy email: [email protected] 2 University of Naples “Federico II”, C.U, Monte Santangelo, Via Cinthia, 80126, Naples, Italy 3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany 4 School of Physics and Astronomy, Sun Yat-sen University Zhuhai Campus, 2 Daxue Road, Tangjia, Zhuhai, Guangdong 519082, P.R. China 5 Kapteyn Astronomical Institute, University of Groningen, PO Box 72, 9700 AV Groningen, The Netherlands 6 Division of Astronomy, Department of Physics, University of Oulu, Oulu, Finland 7 Instituto de Astrofìsica de Canarias, C Via Lactea s/n, 38200 La Laguna, Canary Islands, Spain 8 Departamento de Astrofìsica, Universidad de La Laguna, E-38200 La Laguna, Tenerife, Spain 9 Department of Astrophysics, University of Vienna, Türkenschanzstrasse, 17, 1180 Vienna, Austria 10 INAF-Astronomical Abruzzo Observatory, Via Maggini, 64100, Teramo, Italy 11 INAF - Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy 12 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile 13 INFN - Sezione di Napoli, Napoli, 80126, Italy Received 27 March 2020 ; Accepted 18 June 2020 ABSTRACT 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 sugges- tive of strangulation halting star formation in their outskirts or their Hi-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 10 of the IGL is 6 ± 2 × 10 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 arXiv:2006.11828v2 [astro-ph.GA] 3 Sep 2020 merging in the outskirts of the BGG NGC 1316 and, probably, the disrupted dwarf galaxies close to the group centre. Key words. Surveys – Galaxies: groups: individual: Fornax A – Galaxies: spiral – Galaxies: structure – Galaxies: evolution – Galaxies: photometry 1. Introduction formation, these galaxy clusters are formed from the merging of smaller structures such as galaxy groups (e.g. Blumenthal et al. Galaxies tend to gather in gravitationally bound systems during 1984; Sommer-Larsen 2006; Rudick et al. 2009). The terminol- their evolution, which are seen as dense knots in the cosmic web ogy "galaxy group" and "galaxy cluster" depends on various fac- filaments. In the Local Universe, it has been found that about tors, for example, the galaxy number density, the virial mass, half of the population of galaxies are found in groups and clus- X-ray luminosity, and velocity dispersion. Groups of galaxies ters (Karachentsev 2005). According to the hierarchical structure Article number, page 1 of 27 A&A proofs: manuscript no. Fornax_A_LTGs_AA 13 14 or poor clusters have masses in the range from 10 to 10 M deep photometry (e.g. Zibetti et al. 2005), exploring faint regions (Bower & Balogh 2004; Mamon 2007), and rich clusters are of galaxy outskirts, ICL and IGL have gained importance over 14 more massive > 10 M (e.g. Bahcall 1996). In addition to this, the last years (e.g. Rudick et al. 2009; Mihos et al. 2017; Iodice the intra-cluster medium (ICM) of rich clusters is hotter (X-ray et al. 2016; Spavone et al. 2017a; Iodice et al. 2017a,b; Spavone temperature= 2–14 keV) than that of poor clusters and groups, et al. 2018, and references therein). and the radial velocity dispersion of galaxies in rich clusters is As such, the Fornax cluster has been an environment of higher than that of groups (e.g. Bahcall 1988, 1996). interest. It is the second most massive galaxy concentration The definition of these gravitationally bound systems range within 20 Mpc, after the Virgo cluster, with a virial mass of 13 from binary galaxies to superclusters, all of which are impor- Mvir = 7 × 10 M (Drinkwater et al. 2001a). The Fornax clus- tant in the studies of environmental mechanisms. Several surveys ter has been extensively studied by several surveys in multiple have shown variations in observed properties of galaxies in dif- wavelengths (e.g. Martin & GALEX Team 2005; Scharf et al. ferent environments, that is, from the field to the core of clusters 2005; Jordán et al. 2007; Davies et al. 2013; Muñoz et al. 2015; in the Local Universe (e.g. Lewis et al. 2002; Kauffmann et al. Su et al. 2017; Eigenthaler et al. 2018; Zabel et al. 2019; Serra 2004; Peng et al. 2010; Grootes et al. 2017; Barsanti et al. 2018) et al. 2019). and also at higher redshifts, up to z ∼ 1 (e.g. Poggianti et al. The Fornax Deep Survey (FDS) with the VLT Survey Tele- 2008; Lubin et al. 2009; Cucciati et al. 2010; Cooper et al. 2012; scope (VST, Venhola et al. 2017; Iodice et al. 2019b) is one of Muzzin et al. 2012; Cucciati et al. 2017; Paulino-Afonso et al. the deepest and widest data sets mapping the Fornax cluster out 2018; Guglielmo et al. 2019). Such transitions in galaxy prop- to the virial radius (∼ 0:7 Mpc). With FDS we (i) mapped the sur- erties typically occur around cluster or group scales of ∼ 2–3 face brightness around the brightest cluster members NGC 1399 virial radii (Gómez et al. 2003). One such observed property is and NGC 1316 out to an unprecedented distance of about −2 the decrease in the star formation rate in galaxies of a given mor- ∼ 200 kpc (R ∼ 6Re) and down to µg ' 29–31 mag arcsec phological type in groups and clusters that is visible out to 2r200 (Iodice et al. 2016, 2017b); (ii) traced the spatial distribution (Lewis et al. 2002). The mechanisms causing such changes are of candidate globular clusters (GCs) inside ∼ 0:5 deg2 of the proposed to depend on the local density of the environment and, cluster core (D’Abrusco et al. 2016; Cantiello et al. 2018); hence, they are different in groups and clusters. (iii) studied the galaxy outskirts, detected the ICL and faint −2 The physical processes which are prominent in dense envi- (µg ' 28–30 mag arcsec ) features in the intra-cluster region in ronments of clusters are ram-pressure stripping (Gunn & Gott the core of the cluster (Iodice et al. 2016, 2017a, 2019b; Raj et al. 1972) and harassment (Moore et al. 1996). Ram-pressure strip- 2019) and in the outskirts of NGC 1316 (Iodice et al. 2017b); ping is not prevalent in poor clusters and galaxy groups as it (iv) provided the largest size and magnitude limited catalogue of depends on the velocity of the galaxy and the hot ICM. Mergers dwarf galaxies in the cluster (Venhola et al. 2017, 2018, 2019). and strangulation are more common in groups of galaxies (e.g. The analysis of the deep images from FDS suggests that the Barnes 1985; Zabludoff & Mulchaey 1998). Major mergers can Fornax cluster is not completely relaxed inside the virial ra- significantly alter the morphology of spiral galaxies by destroy- dius. The bulk of the gravitational interactions between galax- ing their discs and therefore producing a major remnant that re- ies takes place in the west-northwest core region, where most of sembles an elliptical galaxy (Dekel et al. 2005). Sometimes, the the bright early-type galaxies (ETGs) are located and where the disc can survive gas-rich mergers albeit resulting in the build-up intra-cluster baryons (i.e.