  We exclude hydrogen burning stars, of any mass above the hydrogen-burning
limit and any metallicity, as significant contributors to the massive halos
deduced from rotation curves to dominate the outer parts of spiral galaxies. We
present and analyse images of 4 nearly edge-on bulgeless spiral galaxies
(UGC711, NGC2915, UGC12426, UGC1459) obtained with ISOCAM (The CAMera
instrument on board the Infrared Space Observatory) at 14.5micron and
6.75micron. Our sensitivity limit for detection of any diffuse infrared
emission associated with the dark halos in these galaxies is a few tens of
microJy per 6arcsec x 6arcsec pixel, with this limit currently set by remaining
difficulties in modelling the non-linear behaviour of the detectors. All four
galaxies show zero detected signal from extended non-disk emission, consistent
with zero halo-like luminosity density distribution. The 95percent upper limit
on any emission, for NGC2915 in particular, allows us to exclude very low mass
main sequence stars (M > 0.08 Msun), and young brown dwarfs (< 1 Gyr) as
significant contributors to dark matter in galactic halos. Combining our
results with those of the Galactic microlensing surveys, which exclude objects
with M < 0.01 Msun, excludes almost the entire possible mass range of compact
baryonic objects from contributing to galactic dark matter.
