The wonderous multi-phase ISM of elliptical galaxies

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Triggered by new observations within the ATLAS$3D survey the picture of the interstellar medium (ISM) in elliptical (early-type) galaxies (ETGs) has changed dramatically over the last two years. Traditionally, ETGs have been considered as simple systems, sometimes containing a reservoir of hot gas but otherwise devoid of a significant multi-phase ISM. Recently, ETGs have been demonstrated to show a structured multi-phase ISM with a significant amount of turbulent cold molecular gas at their centers, warm neutral and ionized gas at larger radii embedded in coronae of hot ionized gas. The gas building up the ISM can originate from cooling of a hot halo - either built up at early times or fed by late infalling gas-rich satellites - or from stellar gas loss of evolving stellar populations. We propose to perform high-resolution three-dimensional hydrodynamic simulations of the multi-phase interstellar medium in ETGs using a novel implementation of smoothed-particle hydrodynamics (SPHgal). The code has improved mixing capabilities, metal diffusion, metal (gas-phase) and energy (momentum) feedback from SNII, SNIa, AGB stars, and AGN. We will address the following fundamental questions: How does a multi-phase interstellar medium develop in massive ETGs in the presence of cooling, feedback from SNII, SNIa, and mass-loss from evolved stellar populations? What is the respective impact of kinetic and thermal feedback and radiation from a nuclear accreting black hole? How can molecular gas form in the extreme environment of the centers of ETGs? This question will be addressed by using a chemical network to follow the formation of H2 and CO in combination with an approximate UV radiative transfer. What is the relative importance of gas cooling from a hot corona, ejected by supernovae, or ejected from AGB stars for the formation of a multi-phase ISM in ETGs? Can feedback from accreting nuclear black holes drive the observed nuclear outflows of molecular gas? How do different galaxy structures affect the answers to the above questions? Within the proposed project we will be able to give a first detailed insight into the new world of the multi-phase ISM of elliptical galaxies.