The wonderous multi-phase ISM of elliptical galaxies

在ATLAS$3D探测的新观测触发下，椭圆(早期类型)星系(ETG)中星际介质(ISM)的图像在过去两年中发生了巨大变化。传统上，ETG一直被认为是简单的系统，有时包含热气藏，但其他情况下没有重要的多相ISM。最近，ETGs被证明是一种有结构的多相ISM，中心有大量的湍流冷分子气体，热电离气体的日冕中嵌入了较大半径的温中性和电离气体。形成ISM的气体可能来自一个热晕的冷却--要么是在早期建立起来的，要么是由后来进入地球的富含气体的卫星提供的--或者来自不断演化的恒星群体的恒星气体损失。我们建议使用一种新的光滑粒子流体动力学方法(SPHga)对ETGS中的多相星际介质进行高分辨率的三维流体动力学模拟。该代码改进了来自SNII、SNIa、AGB STAR和AGN的混合能力、金属扩散、金属(气相)和能量(动量)反馈。我们将解决以下基本问题：在存在冷却、来自SNII、SNIa的反馈以及演化的恒星群的质量损失的情况下，多相星际介质是如何在大质量ETGs中发展的？来自核吸积黑洞的动能、热反馈和辐射分别有什么影响？在ETG中心的极端环境中，分子气体是如何形成的？这个问题将通过使用化学网络来跟踪H2和CO的形成并结合近似的UV辐射转移来解决。热日冕、超新星喷出或AGB恒星喷出的气体冷却对形成ETGs中多相ISM的相对重要性是什么？来自吸积核黑洞的反馈能驱动观测到的分子气体核外流吗？不同的星系结构如何影响上述问题的答案？在拟议的项目中，我们将能够对椭圆星系的多相ISM的新世界进行首次详细的洞察。

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.