VEGAS: A VST Early-type GAlaxy Survey

Abstract

Context. We present the VST Early-type GAlaxy Survey (VEGAS), which is designed to obtain deep multiband photometry in g, r, i, of about one hundred nearby galaxies down to 27.3, 26.8, and 26 mag/arcsec 2 respectively, using the ESO facility VST/OmegaCAM. Aims. The goals of the survey are 1) to map the light distribution up to ten effective radii, r e ; 2) to trace color gradients and surface brightness fluctuation gradients out to a few r e for stellar population characterization; and 3) to obtain a full census of the satellite systems (globular clusters and dwarf galaxies) out to 20% of the galaxy virial radius. The external regions of galaxies retain signatures of the formation and evolution mechanisms that shaped them, and the study of nearby objects enables a detailed analysis of their morphology and interaction features. To clarify the complex variety of formation mechanisms of early-type galaxies (ETGs), wide and deep photometry is the primary observational step, which at the moment has been pursued with only a few dedicated programs. The VEGAS survey has been designated to provide these data for a volume-limited sample with exceptional image quality. Methods. In this commissioning photometric paper we illustrate the capabilities of the survey using g-and i-band VST/OmegaCAM images of the nearby galaxy NGC 4472 and of smaller ETGs in the surrounding field. Results. Our surface brightness profiles reach rather faint levels and agree excellently well with previous literature. Genuine new results concern the detection of an intracluster light tail in NGC 4472 and of various substructures at increasing scales. We have also produced extended (g − i) color profiles. Conclusions. The VST/OmegaCAM data that we acquire in the context of the VEGAS survey provide a detailed view of substructures in the optical emission from extended galaxies, which can be as faint as a hundred times below the sky level.

THE FORNAX DEEP SURVEY WITH VST. I. THE EXTENDED AND DIFFUSE STELLAR HALO OF NGC 1399 OUT TO 192 kpc

“…The absence of a significant number of luminous stellar streams and tidal tails between the galaxies in the core of the Fornax cluster suggests that the epoch of this strong interaction goes back to an early formation epoch. Thus, the extended stellar halo around NGC1399 is characterized by a more diffuse and well-mixed component, including the ICL, with respect to that of M87 or M49 in the Virgo cluster (Mihos et al 2005;Capaccioli et al 2015). This is an indication that the Fornax cluster could be in a more dynamically evolved phase than the Virgo cluster.…”

“…This remains valid even considering that the Virgo cluster is about 3Mpc closer, so the faint structure in the light distribution detected in the Fornax cluster would have an absolute magnitude only ∼0.3mag brighter. On the other hand, at the same faint level of surface brightness, around the giant bright galaxies M49, M86, and M87, several tidal tails are detected, some of them very extended, up to 100 kpc (Mihos et al 2005;Janowiecki et al 2010;Rudick et al 2010;Capaccioli et al 2015;Longobardi et al 2015a). This observational fact might suggest that we are tracing two different epochs of the halo assembly in the two clusters: the Fornax cluster could be in a more dynamically evolved phase (Grillmair et al 1994;Jordán et al 2007), where most of the gravitational interactions between galaxies have already taken place and streams and tails are already dispersed into the intracluster medium or are below the observable surface brightness level.…”

“…R. Peletier) and VEGAS (P.I. M. Capaccioli, Capaccioli et al 2015) being performed at the ESO VST. The VST is a 2.6 m wide-field optical survey telescope, located at Cerro Paranal in Chile (Schipani et al 2012).…”

“…The data reduction has been performed with the VST-Tube imaging pipeline: a detailed description of it, including calibrations and error estimates, is given by Capaccioli et al (2015). The observing strategy adopted for this data set allows us to derive an average sky image from exposures taken as close as possible in space and time to the scientific ones.…”

“…The blue triangles are magnitudes derived from Caon et al (1994), green squares are from Dirsch et al (2003), the red asterisks are the original data from Schombert (1986), and the open red circles are the same magnitudes corrected for a 30% higher value of the sky level. Capaccioli et al (2015) and Seigar et al (2007), the error estimates 11 on the surface brightness magnitudes take the uncertainties on the photometric calibration (∼0.003-0.006 mag) and sky subtraction (∼0.11-0.2 counts) into account. We noticed that, for a large area of the mosaic (∼50 to ∼80 arcmin from the galaxy center), the fluctuations on the background level are not larger than 10% (see bottom panel of Figure 2), whereas, on a smaller range of radii, for 30 R 40 arcmin and for 80 R 90 arcmin from the galaxy center, the deviations from the average zero level of the background affect by about 20% the surface brightness for μ g  27 mag arcsec −2 and μ i   25 mag arcsec −2 .…”