The stellar initial mass function (IMF) seems to be variable and notuniversal, as argued in the literature in the last three decades. Severalrelations among the low-mass end of the IMF slope and other stellar population,photometric or kinematic parameters of massive early-type galaxies (ETGs) havebeen proposed, but a consolidated agreement on a factual cause of the observedvariations has not been reached yet. We investigate the relations between theIMF and other stellar population parameters in NGC 3311, the central galaxy ofthe Hydra I cluster. NGC 3311 is characterized by old and metal-rich stars,like other massive ETGs, but has unusual increasing stellar velocity dispersionand [$\alpha/$Fe] profiles. We use spatially resolved MUSE observations toobtain stellar population properties using Bayesian full-spectrum fitting inthe central part of NGC 3311 to compare the IMF slope against other stellarparameters with the goal of assessing their relations/dependencies. For NGC3311, we unambiguously invalidate the previously observed direct correlationbetween the IMF slope and the local stellar velocity dispersion, confirmingsome doubts already raised in the literature. This relation may arise as aspatial coincidence only, between the region with the largest stellar velocitydispersion, with that where the oldest, $\textit{in situ}$ population is foundand dominates. We also show robust evidence that the proposed IMF-metallicityrelation is contaminated by the degeneracy between these two parameters. Thetightest correlations we found are those between stellar age and IMF andbetween galactocentric radius and IMF. The variation of the IMF is not due tokinematical, dynamical, or global properties in NGC 3311. We speculate that IMFmight be dwarf-dominated in the "red-nuggets" formed at high redshifts thatended up being the central cores of today's giant ellipticals. [Abridged]

The pattern speed with which galactic bars rotate is intimately linked to theamount of dark matter in the inner regions of their host galaxies. Inparticular, dark matter haloes act to slow down bars via torques exertedthrough dynamical friction. Observational studies of barred galaxies tend tofind that bars rotate fast, while hydrodynamical cosmological simulations ofgalaxy formation and evolution in the $\Lambda$CDM framework have previouslyfound that bars slow down excessively. This has led to a growing tensionbetween fast bars and the $\Lambda$CDM cosmological paradigm. In this study werevisit this issue, using the Auriga suite of high resolution,magneto-hydrodynamical cosmological zoom-in simulations of galaxy formation andevolution in the $\Lambda$CDM framework, finding that bars remain fast down to$z=0$. In Auriga, bars form in galaxies that have higher stellar-to-dark matterratios and are more baryon-dominated than in previous cosmological simulations;this suggests that in order for bars to remain fast, massive spiral galaxiesmust lie above the commonly used abundance matching relation. While this workmay resolve the aforementioned tension between fast bars and $\Lambda$CDM, itaccentuates the recently reported discrepancy between the dynamically inferredstellar-to-dark matter ratios of massive spirals and those inferred fromabundance matching. Our results highlight the potential of using bar dynamicsto constrain models of galaxy formation and evolution.

The characterization of the large amount of gas residing in the galaxy halos,the so called circumgalactic medium (CGM), is crucial to understand galaxyevolution across cosmic time. We focus here on the the cool ($T\sim10^4$ K)phase of this medium around star-forming galaxies in the local universe, whoseproperties and dynamics are poorly understood. We developed semi-analyticalparametric models to describe the cool CGM as an outflow of gas clouds from thecentral galaxy, as a result of supernova explosions in the disc (galacticwind). The cloud motion is driven by the galaxy gravitational pull and by theinteractions with the hot ($T\sim10^6$ K) coronal gas. Through a bayesiananalysis, we compare the predictions of our models with the data of theCOS-Halos and COS-GASS surveys, which provide accurate kinematic information ofthe cool CGM around more than 40 low-redshift star-forming galaxies, probingdistances up to the galaxy virial radii. Our findings clearly show that asupernova-driven outflow model is not suitable to describe the dynamics of thecool circumgalactic gas. Indeed, to reproduce the data, we need extremescenarios, with initial outflow velocities and mass loading factors that wouldlead to unphysically high energy coupling from the supernovae to the gas andwith supernova efficiencies largely exceeding unity. This strongly suggeststhat, since the outflows cannot reproduce most of the cool gas absorbers, thelatter are likely the result of cosmological inflow in the outer galaxy halos,in analogy to what we have previously found for early-type galaxies.