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Based on MUSE integral-field data we present evidence for a radial variationat the low-mass end of the stellar initial-mass function (IMF) in the centralregions of the giant early-type galaxy NGC4486 (M87). We used state-of-the-artstellar population models and the observed strength of various IMF-sensitiveabsorption-line features to solve for the best low-mass tapered "bimodal" formof the IMF, while accounting also for radial variations in stellar metallicity,the overall $\alpha$-elements abundance, and the abundance of individualelements such as Ti, O, Na and Ca. Our analysis reveals a strong IMF gradientin M87, corresponding to an exceeding fraction of low-mass stars compared tothe case of the Milky Way toward the center of M87 that drops to nearlyMilky-way levels by 0.4 $R_e$. This IMF gradient is found to correlate wellwith both the radial profile for stellar metallicity and for $\alpha$-elementsabundance but not with stellar velocity dispersion. Such IMF variationscorrespond to over a factor two increase in stellar mass-to-light M/L ratiocompared to the case of a Milky-way like IMF, consistent with otherinvestigations into IMF gradients in early-type galaxies, including recentdynamical constraints on M/L radial variations in M87 by Oldham & Auger. Inaddition to constraining the IMF in M87 we also looked into the abundance ofSodium, which turned up to be super-Solar over the entire radial range of ourMUSE observations and to exhibit a considerable negative gradient. Thesefindings suggest an additional role of metallicity in boosting the Na-yields inthe central, metal-rich regions of M87 during its early and briefstar-formation history. Our work adds the case of M87 to the few objects thatas of today have radial constraints on their IMF or [Na/Fe] abundance, whilealso illustrating the accuracy that MUSE could bring to this kind ofinvestigations.

MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium