Abstract
Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraints on the cosmological context of galaxy assembly in the Λ CDM 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 VST Elliptical GAlaxies Survey (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.
Highlights
Theories of galaxy formation within the currently accepted Λ Cold Dark Matter cosmological paradigm predict that galaxies grow through a combination of in situ star formation and accretion of stars from other galaxies [1]
The large field of view (FOV) of the OmegaCAM mounted on VLT Survey Telescope (VST), together with its high efficiency and spatial resolution allows us to map with a reasonable integration time the surface brightness of a galaxy out to isophotes encircling about 95% of the total light
We adopt an empirically motivated, two-component approach most common in the literature, as well as an alternative approach, which is motivated by the predictions of numerical simulations, in which we fitted the surface brightness profiles of our galaxies with three components: two dominant
Summary
Theories of galaxy formation within the currently accepted Λ Cold Dark Matter cosmological paradigm predict that galaxies grow through a combination of in situ star formation and accretion of stars from other galaxies [1]. In this paper we use extremely deep images of six massive early-type galaxies (ETGs) from the VEGAS survey (described below) to constrain the properties of their accreted stellar components. Simulated galaxies show evidence of substructure in the form of inflections (‘breaks’), at which the surface brightness profile either becomes steeper or shallower (e.g., [3,4]). These inflections correspond to variations in the ratio between individual accreted components as a function of radius [5,6,7]. Observatory (Chile), we carried out deep and detailed photometric mapping of six massive early-type galaxies (ETGs) in the VEGAS sample
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