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The Initial Mass Function

Martin-Navarro et al. (2015a) Martin-Navarro et al. (2015b) Martin-Navarro et al. (2015c) Martin-Navarro et al. (2019)

Of extreme importance to understand the star formation and feedback puzzle is to know the mass distribution of stars when they are formed, the so-called initial mass function (IMF). The traditionally adopted universality of the IMF has been challenged both, on star-forming and on quiescent systems (e.g., La Barbera+2013; Zhang+2018). Regarding the latter, spectral features that are sensitive to the giant vs dwarf stellar ratio have been used as a discriminant of the IMF. The finding of bottom-heavy IMF in massive early-type galaxies (e.g., van Dokkum & Conroy 2010; Cenarro+2003) was later supported by dynamical studies (Capellari+2012) and may be the consequence of the different physical properties of the insterstellar medium when these galaxies formed their stars. However, what is exactly the physical driver of the observed IMF variations remains debated. To aid theorists, we searched for correlations between the observed IMF and other properties of the galaxies. In (Martin-Navarro et al. 2015a; Martin-Navarro et al. 2015b; La Barbera et al. 2016) we showed, for the first time, that enhanced dwarf-to-giant ratio was only present in the cores of massive galaxies and seemed to follow stellar metallicity). However, analyses of a much larger sample (Martin-Navarro et al. 2019) indicates that changes in the metallicity were not able to fully explain IMF variations and that, interestingly, there seems to exist a suggestive connection between low angular momentum orbits and the 2D distribution of the IMF.

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AGN feedback

Martin-Navarro & Mezcua (2018, ApJL, 855, L20) Martin-Navarro et al. (2018, Nature, 553, 307) del Moral-Castro et al. (2019)

The bulk of the population of massive galaxies appear red and dead (not forming stars) at the present time. This so-called quenching of star-formation is one of the most poorly understood yet fundamental aspects of galaxy evolution. As stellar feedback is not powerful enough to expel the gas from the strong potential wells of these galaxies, standard explanations invoke AGN as the main agent for massive galaxy quenching. This explanation seems to be supported by the observed co-evolution of galaxies and their central black holes (e.g., Magorrian+2018), which could indicate that all galaxies experience nuclear activity for at least some part of their evolution. Despite its critical role in our understanding of galaxy evolution, we still do not know (1) the mechanism(s) that trigger an AGN or (2) its effect on galaxy properties.

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AGN in cosmological simulations

Perucho et al. (2017, MNRAS, 471, L120) Perucho et al. (2019, MNRAS, 482, 3718)

We use magneto-hydrodynamical simulations to understand the interplay between jets and the ambient medium in both, galaxies and clusters. An important result was to show that the efficiency of the energy transfer to the ambient medium, as well as the spatial and temporal scales involved, can be very different for relativistic (both kinematically and thermodynamically) and non-relativistic jets .