  Dust enshrouded activity can ideally be studied by mid-infrared (MIR)
observations. In order to explore the AGN versus star forming origin of the
nuclear MIR emission of galaxies, observations of high spatial resolution are
required. Here we report on 11.3mic. observations with VISIR at the VLT,
reaching 0.35'' spatial resolution (FWHM). During the scientific verification
of VISIR we have observed a sample of 36 nearby galaxies having a variety of
optically classified nuclear activity: 17 black hole driven active galactic
nuclei (AGN), 10 starbursts (SBs) and 9 quiet spirals. 16/17 AGN are detected
and unresolved, 5/10 SBs are detected and resolved with structured emission up
to a few arcsec, while for 5/10 SB and all 9 quiet nuclei low upper limits are
provided. The morphology of the resolved SB nuclei follows that seen at radio
frequencies. The compactness of AGN and the extent of the SB nuclei is
consistent with predictions from radiative transfer models and with MIR spectra
of lower spatial resolution. We explore the nuclear MIR surface brightness as a
quantitative measure. While AGN and SB cannot be distinguished with MIR data
from 4m class telescopes, our data provide evidence that, up to a distance of
100 Mpc, AGN and SB can well be separated by means of MIR surface brightness
when using 8m class telescopes.
