Ignacio Martín-NavarroLA BARBERA, FrancescoFrancescoLA BARBERAAlexandre VazdekisJesús Falcón-BarrosoIgnacio Ferreras2021-04-222021-04-2220150035-8711http://hdl.handle.net/20.500.12386/30846The hypothesis of a universal initial mass function (IMF) -- motivated by observations in nearby stellar systems -- has been recently challenged by the discovery of a systematic variation of the IMF with the central velocity dispersion, {\sigma}, of early-type galaxies (ETGs), towards an excess of low-mass stars in high-{\sigma} galaxies. This trend has been derived so far from integrated spectra, and remains unexplained at present. To test whether such trend depends on the local properties within a galaxy, we have obtained new, extremely deep, spectroscopic data, for three nearby ETGs, two galaxies with high {\sigma} (~300 km/s), and one lower mass system, with {\sigma} ~ 100 km/s. From the analysis of IMF-sensitive spectral features, we find that the IMF depends significantly on galactocentric distance in the massive ETGs, with the enhanced fraction of low-mass stars f mostly confined to their central regions. In contrast, the low-{\sigma} galaxy does not show any significant radial gradient in the IMF, well described by a shallower distribution, relative to the innermost regions of massive galaxies, at all radii. Such a result indicates that the IMF should be regarded as a local (rather than global) property, and suggests a significant difference between the formation process of the core and the outer regions of massive ETGs.STAMPAenArticle10.1093/mnras/stu24802-s2.0-84922522658http://arxiv.org/abs/1404.6533v2https://academic.oup.com/mnras/article/447/2/1033/25936502015MNRAS.447.1033MFIS/05 - ASTRONOMIA E ASTROFISICA