VEGAS: A VST Early-type GAlaxy Survey

II. Photometric study of giant ellipticals and their stellar halos

¹ INAF–Astronomical Observatory of Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
e-mail: spavone@na.astro.it
² University of Naples Federico II, C.U. Monte Sant’Angelo, via Cinthia, 80126 Naples, Italy
³ INAF–Astronomical Observatory of Teramo, via Maggini, 64100 Teramo, Italy
⁴ Institute for Computational Cosmology, Durham DH13, UK
⁵ Centre for Astrophysics & Supercomputing, Swinburne University, Hawthorn, VIC 3122, Australia

Received: 14 June 2016
Accepted: 30 March 2017

Abstract

Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraint on the cosmological context of galaxy assembly in the ΛCDM model. Such observations are not trivial because of the extreme faintness of such regions. In this work, we investigated the photometric properties of six massive early-type galaxies (ETGs) in the VEGAS sample (NGC 1399, NGC 3923, NGC 4365, NGC 4472, NGC 5044, and NGC 5846) out to extremely low surface brightness levels with the goal of characterizing the global structure of their light profiles for comparison to state-of-the-art galaxy formation models. We carried out deep and detailed photometric mapping of our ETG sample taking advantage of deep imaging with VST/OmegaCAM in the g and i bands. By fitting the light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in situ and accreted stars. The very good agreement of our results with predictions from theoretical simulations demonstrates that the full VEGAS sample of ~100 ETGs will allow us to use the distribution of diffuse light as a robust statistical probe of the hierarchical assembly of massive galaxies.