VEGAS: a VST Early-type GAlaxy Survey

Abstract

Context. This paper is based on the multi-band VST Early-type GAlaxy Survey (VEGAS) with the VLT Survey Telescope (VST). We present new deep photometry of the IC 1459 group in g and r band. Aims. The main goal of this work is to investigate the photometric properties of the IC 1459 group, and to compare our results with those obtained for other galaxy groups studied in VEGAS, in order to provide an initial view of the variation of their properties as a function of the evolution of the system. Methods. For all galaxies in the IC 1459 group, we fit isophotes and extract the azimuthally averaged surface-brightness profiles, the position angle, and ellipticity profiles as a function of the semi-major axis. We also extract the average colour profile. In each band, we estimate the total magnitude, effective radius, mean colour, and total stellar mass for each galaxy in the group. We then look at the structure of the brightest galaxies and the faint features in their outskirts, considering also the intragroup component. Results. The wide field of view, long integration time, high angular resolution, and arcsec-level seeing of OmegaCAM at VST allow us to map the light distribution of IC 1459 down to a surface brightness level of 29.26 mag arcsec−2 in g band and 28.85 mag arcsec−2 in r band, and out to 7−10Re, and to detect the optical counterpart of HI gas around IC 1459. We also carry out an in-depth exploration of three low-density environments and provide information to understand how galaxy and group properties change with the group evolution stage. Conclusions. Good agreement is found between our results and predictions of numerical simulations regarding the structural properties of the brightest galaxies of the groups. We suggest that the structure of the outer envelope of he brightest cluster galaxies (i.e. the signatures of past mergers and tidal interactions), the intra-group light, and the HI amount and distribution may be used as indicators of the evolutionary stage and mass assembly of galaxy groups.

The Fornax Deep Survey with VST

“…FCC 276 has bluer colours (g − r ∼ 0.3 mag), comparable colours to the ETGs in the low-density region of the cluster, but a high accreted mass fraction ( f h,T = 0.87) that is consistent with that typical for all the others ETGs in the high-density region of the cluster, suggesting that this galaxy might be in a transition phase of mass assembly. In particular the bluer colours are related to a distinct kinematical component in the centre (R 10 arcsec), which has v max ∼ 50 km s −1 and σ ∼ 180 km s −1 (Carollo et al 1997;Iodice et al 2019bIodice et al , 2020.…”

“…The un-relaxed component of the stellar envelope appears as a change in the slope at larger radii of the surface brightness profiles. In this context, the study of the surface brightness profiles of galaxies at the faintest levels is potentially one of the main tools available to quantify the contribution of the accreted mass, which becomes particularly efficient when the outer stellar envelope starts to be dominant beyond the transition radius (Iodice et al 2016(Iodice et al , 2017a(Iodice et al , 2020Spavone et al 2017Spavone et al , 2018. To this aim, in this paper we used the r-band azimuthally averaged surface brightness profiles of ETGs inside the virial radius of the Fornax cluster (Iodice et al 2019b) to perform a multi-component fit to estimate the relative contribution of the accreted component with respect to that formed in situ.…”

The Fornax Deep Survey with VST

“…Although the Fornax A subgroup has the lowest ratio among the groups discussed above, a major fraction of the IGL with respect to the IC 1459 group, which has comparable ETG-to-LTG ratio, comes from the past merger of NGC 1316 and disrupted dwarf galaxies. In the IC 1459, no signs of interactions are found with a galaxy of comparable mass (Iodice et al 2020).…”

“…In the Fornax A group, as well as in the NGC 1533 triplet (Cattapan et al 2019), that have a comparable IGL fraction, mergers would have partly contributed to the IGL, and signs of past mergers are confined in the BGG's envelope (in the form of loops and shells). As pointed out by Iodice et al (2020), given the low IGL fraction (∼2%) and the structure and properties of galaxy members, the IC 1459 group is still in an early mass assembly phase.…”

“…8 we also compare the IGL derived for the Fornax A group with values obtained for other groups of galaxies, from observations of comparable depth and with the same image analysis. In particular, we plot the fraction of IGL to the total luminosity of the bright member galaxies as a function of the BGG stellar mass (in the range 10 11 -10 12 M ) for four groups: Fornax A (NGC 1316), NGC 5018 (Spavone et al 2018), NGC 1533 (Cattapan et al 2019), and IC 1459 (Iodice et al 2020). Compared with theoretical predictions, the IGL fraction in each group reflects their assembly history.…”