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Fig. 5


Residuals after an average passive ETG spectrum (the thick black profile, see also Fig. 2) has been subtracted. As an example, on the top of the average passive spectrum, we plot the NGC 1366 spectrum. We collect Class-1 ETGs, with ionic and molecular emission lines but without clear PAH emission. Residual fluxes, arbitrarily scaled, confirm the lack of PAH features. Emission lines detected are indicated on the top of the plot. The NGC 4696 spectrum shows H2 S(1) and S(3) rotational lines.

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