  Massive Early-Type Galaxies (ETGs) show several strong CO absorption features
in their H- and K-band spectra that cannot be explained by state-of-the-art
stellar population models. For many years, the disagreement has been attributed
to the presence of intermediate-age stellar components that are dominated by
stars in the Asymptotic Giant Branch (AGB) phase. However, no robust evidence
of this scenario has been provided so far. One way to test this claim is by
comparison of CO indices for ETGs and for relic galaxies. Lacking the
intermediate-age stellar populations, relic galaxies provide us with a unique
opportunity to address the origin of strong CO absorptions in ETGs. Here, we
utilize the prototype relic galaxy NGC 1277 and compare the CO absorption
features of this galaxy with the ones of a representative sample of massive
ETGs. We show that the CO lines in both systems have similar strengths,
significantly stronger than the predictions of stellar population synthesis
models. We conclude that intermediate-age stellar populations in massive ETGs
are not the culprit of the strong CO absorptions.
