Stellar population studies can lead to different results for the same data depending on the choice of, for example, the models, the cosmology adopted, the wavelength range, the selection limits, the use of spectroscopy vs photometry, etc. For some of these, the user can freely choose, while others are assumed to be universal. This is the case of the Initial Mass Function (IMF), a fundamental parameter on the stellar population analysis, as it describes the distribution of the stellar masses in a single population of stars at the time of birth. For decades, it has been assumed to be universal, showing the same shape and steepness for all types of galaxies at all epochs.

However, recent results have claimed that this is no longer the case. In particular, it has been shown, from several approaches and techniques, that more massive galaxies demand steeper IMF slopes. In addition, it seems that a systematic correlation with the IMF slope and the velocity dispersion exists. If this is the case, this has a strong impact on our previous works, as we were characterizing massive galaxies assuming the standard Kroupa IMF.