VEGAS: A VST Early-type GAlaxy Survey

Abstract

Context. In this paper, we present ultra-deep images of the compact group of galaxies HCG 86 as part of the VEGAS survey. Aims. Our main goals are to estimate the amount of intra-group light (IGL) as well as to study the light and colour distributions in order to address the main formation process of the IGL component in groups of galaxies. Methods. We derived the azimuthally averaged surface brightness profiles in the g, r, and i bands with g − r and r − i average colours and colour profiles for all group members. By fitting the light distribution, we extrapolated the contribution of the stellar halos plus the diffuse light from the brightest component of each galaxy. The results are compared with theoretical predictions. Results. The long integration time and wide area covered make our data reach deeper than previous literature studies of the IGL in compact groups of galaxies and allow us to produce an extended (∼160 kpc) map of the IGL, down to a surface brightness level of ∼30 mag arcsec−2 in the g band. The IGL in HCG 86 is mainly in diffuse form and has average colours of g − r ∼ 0.8 mag and r − i ∼ 0.4 mag. The fraction of IGL in HCG 86 is ∼16% of the total luminosity of the group, and this is consistent with estimates available for other compact groups and loose groups of galaxies of similar virial masses. A weak trend is present between the amount of IGL and the early-type to late-type galaxy ratio. A lack of a clear correlation is found between the amount of diffuse light and the cluster or group virial mass. Conclusions. By comparing the IGL fraction and colours with those predicted by simulations, the amount of IGL in HCG 86 would be the result of the disruption of satellites at an epoch of z ∼ 0.4. At this redshift, the observed colours are consistent with the scenario where the main contribution to the mass of the IGL comes from the intermediate-to-massive galaxies (1010 ≤ M* ≤ 1011 M⊙).

The Intra-Group Baryons in the LEO I Pair From the VST Early-Type GAlaxy Survey

“…The main steps we performed for the data analysis are briefly summarised below and discussed in detail in the next subsections. They have been tested and successfully applied to all VST images [see (Iodice et al, 2017;Spavone et al, 2018;Iodice et al, 2019a;Cattapan et al, 2019;Iodice et al, 2020;Raj et al, 2020;Spavone et al, 2020;Ragusa et al, 2021), and references therein], to study the LSB regime, in particular to detect the IGL. For the estimate and analysis of the IGL we use the g and r bands only, since these are the deepest images with the most efficient filters of OmegaCAM.…”

“…Using the same method described by Ragusa et al (Ragusa et al, 2021), the star-subtracted images are used to estimate the R lim and the average value of the residual background level4. Since images are sky-subtracted the residual background level is close to zero.…”

“…On the observational side, Sampaio-Santos et al (Sampaio-Santos et al, 2020) for a sample of 528 clusters at 0.2 ≤ z ≤ 0.35, didn't find an increasing dependence between the amount of ICL and M vir . Also from observations in the local Universe (z ≤ 0.05) it seems there is no evident relationship between the ICL fraction and the M vir [e.g., (Ragusa et al, 2021), and reference therein]. A large scatter is observed, where high ICL amount (~30-45%) occurs both in groups with and in massive clusters of galaxies, like Fornax and Antlia (Ragusa et al, 2022 in preparation), as well as low ICL amount (~5-10%) results both in groups and in massive clusters of galaxies, like Coma and Abell85 (Jiménez-Teja et al, 2019;Montes et al, 2021).…”

“…The VST Early-type GAlaxy Survey (Capaccioli et al, 2015) takes its place in this context as a pivotal survey with an increasingly important role in the development of the deep and wide-field photometry. VEGAS1 is a multi-band u, g, r, i imaging survey, able to map the surface brightness of galaxy down to the azimuthally averaged surface brightness μ g ~31 mag arcsec −2 and out to ~15 effective radii (R e ) [see (Iodice et al, 2017;Spavone et al, 2018;Iodice et al, 2019a;Cattapan et al, 2019;Iodice et al, 2020;Raj et al, 2020;Spavone et al, 2020;Ragusa et al, 2021), and references therein]. In this work we present new deep data of the LEO I pair, NGC 3379-NGC 3384, as part of the VEGAS sample.…”

The Transition Region between Brightest Cluster Galaxies and Intra-Cluster Light in Galaxy Groups and Clusters

“…In fact, the validity of the results presented in this work depends on the accuracy of our semi-analytic model in predicting the right amounts of the BCG and ICL masses. Starting from the latter, it has been shown in several works, theoretical (e.g., Contini et al 2014;Tang et al 2018;Henden et al 2020;Cañas et al 2020;Alonso Asensio et al 2020) but most importantly observational (e.g., Montes & Trujillo 2014;Edwards et al 2016;Harris et al 2017;Alamo-Martínez & Blakeslee 2017;Montes & Trujillo 2018;DeMaio et al 2018;Edwards et al 2020;DeMaio et al 2020;Spavone et al 2020;Raj et al 2020;Ragusa et al 2021;Furnell et al 2021;Chen et al 2021;Yoo et al 2021), that our semi-analytic model provides a good description of the formation and evolution of the ICL. Not just its mass at different redshifts, or the fraction as a function of halo mass, but several other properties that have been confirmed by observational studies.…”