A deep view on the Virgo cluster core

Abstract

Studies of dwarf spheroidal (dSph) galaxies with statistically significant sample sizes are still rare beyond the Local Group, since these low surface brightness objects can only be identified with deep imaging data. In galaxy clusters, where they constitute the dominant population in terms of number, they represent the faint end slope of the galaxy luminosity function and provide important insight on the interplay between galaxy mass and environment. In this study we investigate the optical photometric properties of early-type galaxies (dwarf ellipticals (dEs) and dSphs) in the Virgo cluster core region, by analysing their location on the colour magnitude relation (CMR) and the structural scaling relations down to faint magnitudes, and by constructing the luminosity function to compare it with theoretical expectations. Our work is based on deep CFHT V-and I-band data covering several square degrees of the Virgo cluster core that were obtained in 1999 using the CFH12K instrument. We visually select potential cluster members based on morphology and angular size, excluding spiral galaxies. A photometric analysis has been carried out for 295 galaxies, using surface brightness profile shape and colour as further criteria to identify probable background contaminants. 216 galaxies are considered to be certain or probable Virgo cluster members. Our study reveals 77 galaxies not catalogued in the VCC (with 13 of them already found in previous studies) that are very likely Virgo cluster members because they follow the Virgo CMR and exhibit low Sérsic indices. Those galaxies reach M V = −8.7 mag. The CMR shows a clear change in slope from dEs to dSphs, while the scatter of the CMR in the dSph regime does not increase significantly. Our sample might, however, be somewhat biased towards redder colours. The scaling relations given by the dEs appear to be continued by the dSphs indicating a similar origin. The observed change in the CMR slope may mark the point at which gas loss prevented significant metal enrichment. The almost constant scatter around the CMR possibly indicates a short formation period, resulting in similar stellar populations. The luminosity function shows a Schechter function's faint end slope of α = −1.50 ± 0.17, implying a lack of galaxies related to the expected number of low-mass dark matter haloes from theoretical models. Our findings could be explained by suppressed star formation in low-mass dark matter halos or by tidal disruption of dwarfs in the dense core region of the cluster.

An extensive catalogue of early-type galaxies in the nearby Universe

“…Column 11 lists the identification number of the galaxy in the catalogue of Virgo cluster galaxies by Lieder et al (2012), [LHH2012].…”

“…These values have generally already been corrected for Galactic foreground extinction (McConnachie 2012). A '8' indicates that the galaxy is a member of the Virgo Cluster whose value for mV comes from Lieder et al (2012). A '9' indicates that the galaxy is a member of the Hydra Cluster whose extinction-corrected value for mV comes from Misgeld et al (2008).…”

“…As with the magnitudes, we prefer data on (V − I) from Karick et al (2003) over those from Mieske et al (2007). A '5' indicates that the colour has been calculated based data on mV and mI from Lieder et al (2012) for the Virgo Cluster. A '6' indicates that the colour has been calculated based on data on mV and mI from Misgeld et al (2008) for the Hercules Cluster.…”

“…ǫ = 0. A '11' indicates that the galaxy is part of the Virgo cluster and its Re is based on the physical Re published by Lieder et al (2012). A '12' indicates galaxies in the Hydra cluster whose Re is based on the angular Re in Misgeld et al (2008).…”

A normal abundance of faint satellites in the fossil group NGC 6482

“…In particular for galaxies with faint total magnitudes, this would indicate that they are background galaxies following Lieder et al (2012).…”