  As part of the CALIFA survey, we conducted a thorough 2D analysis of the
ionized gas in two E/S0 galaxies, NGC6762 and NGC5966, aiming to shed light on
the nature of their warm ionized ISM. We present optical IFS obtained with the
PMAS/PPAK spectrophotometer. To recover the nebular lines, we subtracted the
underlying stellar continuum from the observed spectra using the STARLIGHT
code. In NGC6762, the ionized gas and stellar emission display similar
morphologies, while the emission line morphology is elongated in NGC5966,
spanning ~6 kpc, and is oriented roughly orthogonal to the major axis of the
stellar continuum ellipsoid. Whereas gas and stars are kinematically aligned in
NGC6762, the gas is kinematically decoupled from the stars in NGC5966. A
decoupled rotating disk or an ionization cone are two possible interpretations
of the elongated ionized gas structure in NGC5966. The latter would be the
first ionization cone of such a dimension detected within a weak emission-line
galaxy. Both galaxies have weak emission-lines relative to the continuum
[EW(Ha)< 3 A] and have low excitation, log([OIII]5007/Hb) < 0.5. Based on
optical diagnostic ratios
([OIII]5007/Hb,[NII]6584/Ha,[SII]6717,6731/Ha,[OI]6300/Ha), both objects
contain a LINER nucleus and an extended LINER-like gas emission. The emission
line ratios do not vary significantly with radius or aperture, which indicates
that the nebular properties are spatially homogeneous. The gas emission in
NGC6762 can be best explained by photoionization by pAGB stars without the need
of invoking any other excitation mechanism. In the case of NGC5966, the
presence of a nuclear ionizing source seems to be required to shape the
elongated gas emission feature in the ionization cone scenario, although
ionization by pAGB stars cannot be ruled out.(abridged)
