We have employed FORS1 and 2 at the Very Large Telescope at ESO to acquire deep B and R -band CCD images of 16 dwarf elliptical galaxies in the direction of the Virgo cluster .
For each dwarf we measure the apparent R -band surface brightness fluctuation ( SBF ) magnitude \overline { m } _ { R } and the ( B - R ) _ { 0 } colour in a number of fields at different galactocentric distances .
From the field-to-field variation of the two quantities we determine the SBF distance by means of the ( B - R ) _ { 0 } - \overline { M } _ { R } relation .
The derived distances of the dwarfs are ranging from 14.9 Mpc to 21.3 Mpc , with a mean 1 \sigma uncertainty of 1.4 Mpc or 8 % of the distance , confirming that there is considerable depth in the distance distribution of early-type cluster members .
For VCC1104 ( IC3388 ) our SBF distance modulus of ( m - M ) _ { SBF } = 31.15 \pm 0.19 ( 17.0 \pm 1.5 Mpc ) is in good agreement with the Harris et al .
( 1998 ) result of ( m - M ) _ { TRGB } = 30.98 \pm 0.19 mag ( 15.7 \pm 1.5 Mpc ) based on HST observations and the tip magnitude of the red giant branch .
Combining our results with existing distances for giant Virgo ellipticals we identify two major galaxy concentrations in the distance distribution : a broad primary clump around ( M - m ) = 31.0 mag ( 15.8 Mpc ) and a narrow secondary clump around 31.33 mag ( 18.5 Mpc ) .
An adaptive kernel analysis finds the two concentrations to be significant at the 99 % ( 2.5 \sigma ) and 89 % ( 1.6 \sigma ) levels .
While the near-side clump of Virgo early-type galaxies can be associated to the subcluster centered on M87 , the second clump is believed to be mainly due to the backside infalling group of galaxies around M86 . The ages and metallicities of the dE stellar populations are estimated by combining the observed ( B - R ) _ { 0 } colours with Worthey ’ s stellar population synthesis models .
It appears that the Virgo dEs cover a wider range in metallicity , from [ Fe/H ] \approx - 1.4 
( VCC0815 ) to -0.5 ( NGC4415 ) , than Fornax cluster dEs .
The derived metallicities place the Virgo dEs on the extension of the metallicity–luminosity relation defined by the low-luminousity Local Group dEs .
The data further suggest an age range from genuinly old ( \sim 17 Gyrs ) stellar systems like IC3019 and IC0783 to intermediate-age ( 8 - 12 Gyrs ) dwarfs like NGC4431 and IC3468 .