  We have observed emission line objects located in a 0.26 deg^2 field in the
M96 (Leo) group, coincident with the intergalactic HI cloud. The emission line
objects were selected using the same procedure as used for the search for
intracluster planetary nebulae in the Virgo cluster, and their m_5007
luminosity function has a bright cut-off ~1.2 magnitude fainter than for the
PNLF associated with the elliptical galaxies in the M96 group.Therefore the
vast majority of these emission line objects are compatible with not being
intragroup planetary nebulae at the Leo group distance of 10 Mpc. Spectroscopic
follow-up of two emission line objects in this Leo field showed that indeed
these do not have the [OIII] doublet expected for a real PN. The brighter
source is identified as a starburst object at redshift z = 3.128, because of a
second emission in the near infrared, identified as FeII (\lambda 2220 AA).
  From these data we derive three main results: (i) from the absence of PN we
can determine a more stringent upper limit to the surface brightness in any old
stellar population associated with the Leo HI cloud. (ii) This translates to an
upper limit of 1.6% for the fraction of luminosity in a diffuse intragroup
component in the densest 3 x 2 deg area of the Leo group,relative to the light
in galaxies. (iii) Using this Leo field as a blank field, we derive an average
fraction of 13.6% background emission line objects that enter in surveys of
Virgo intracluster PN. The small fraction confirms the validity of the
selection criteria for intracluster PN candidates in Virgo.
