As part of the ongoing CALIFA survey , we have conducted a thorough bidimensional analysis of the ionized gas in two E/S0 galaxies , NGC 6762 and NGC 5966 , aiming to shed light on the nature of their warm ionized ISM .
Specifically , we present optical ( 3745-7300 Å ) integral field spectroscopy obtained with the PMAS/PPAK integral field spectrophotometer .
Its wide field-of-view ( 1 \arcmin x 1 \arcmin ) covers the entire optical extent of each galaxy down to faint continuum surface brightnesses .
To recover the nebular lines , we modeled and subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT spectral synthesis code .
The pure emission-line spectra were used to investigate the gas properties and determine the possible sources of ionization .
We show the advantages of IFU data in interpreting the complex nature of the ionized gas in NGC 6762 and NGC 5966 .
In NGC 6762 , the ionized gas and stellar emission display similar morphologies , while the emission line morphology is elongated in NGC 5966 , spanning \sim 6 kpc , and is oriented roughly orthogonal to the major axis of the stellar continuum ellipsoid .
Whereas gas and stars are kinematically aligned in NGC 6762 , the gas is kinematically decoupled from the stars in NGC 5966 .
A decoupled rotating disk or an “ ionization cone ” are two possible interpretations of the elongated ionized gas structure in NGC 5966 .
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 ( H \alpha ) \lesssim 3 Å ] and have very low excitation , log ( [ O iii ] \lambda 5007/H \beta ) \lesssim 0.5 .
Based on optical diagnostic ratios ( [ O iii ] \lambda 5007/H \beta , [ N ii ] \lambda 6584/H \alpha , [ S ii ] \lambda 6717,6731/H \alpha , [ O i ] \lambda 6300/H \alpha ) , 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 NGC 6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism .
In the case of NGC 5966 , 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 can not be ruled out .
Further study of this object is needed to clarify the nature of its elongated gas structure .