星系中原子和分子气体的半解析模型

发布时间：2018-06-25 00:31

本文选题：分子气体 + 解析模型　；参考：《天文学进展》2011年04期

【摘要】：星际气体是星系中重子物质的重要组成部分,其中的分子气体(主要是分子氢H_2)以及原子气体(主要是中性氢HI)对于星系中发生的各个物理过程至关重要。本文在前人的星系形成和演化的半解析模型基础上,加入了描述星系盘中分子气体和原子气体成分的物理模型,来研究分子气体和原子气体对于星系形成和演化所起的作用。我们主要使用了马普天体物理所Munich Group的L-Galaxies半解析星系形成模型,并借鉴了星系化学演化模型的方法,把半解析模型中的每一个星系盘分成了多个同心圆圈,然后在每个圈中分别追踪气体下落、分子气体和原子气体转化、恒星形成、金属增丰、超新星爆发加热冷气体等发生在星系盘上的物理过程,并且每个同心圈都是独立演化的。在我们的模型中,一个基本假设是每个时间步内气体都是以指数形式下落到星系盘上,并且直接叠加在已有的气体径向面密度轮廓之上,其中指数盘的标长r_d正比于星系所在暗物质晕的维里半径r_(vir)与旋转参量λ的乘积。我们的模型使用了两种描述分子气体形成的模型:一种是基于Krumholz等人解析模型的结果,其中分子气体的比例与局域气体面密度以及局域气体金属丰度相关;另一种是分子气体比例与星际压强相关的模型,根据Obreschkow等人的近似,分子气体的比例与气体面密度以及恒星质量面密度相关。由于恒星形成过程发生在星际巨分子云之中,并且根据Leroy等人的观测结果,恒星形成率面密度近似正比于分子气体的面密度,因此我们在模型中使用了与分子气体面密度相关的恒星形成规律。
[Abstract]:Interstellar gas is an important part of the Baryons in galaxies. The molecular gases (mainly molecular hydrogen H_2) and atomic gases (mainly neutral hydrogen HI) are essential for the physical processes occurring in galaxies. This paper, on the basis of the semi analytical model of the formation and evolution of previous galaxies, has added a description of the molecules in the galactic disk. The physical model of gas and atomic gas components is used to study the effect of molecular and atomic gases on the formation and evolution of galaxies. We mainly use the L-Galaxies semi analytic galaxy formation model of Munich Group in MP physics, and draw on the method of galactic chemical evolution model for each star in the semi analytical model. The disc is divided into multiple concentric circles, and then in each circle, the gas falls, molecular gas and atomic gas are converted, star formation, metal enrichment, supernova explosion and cold gas are heated on the galactic disk, and each concentric circle is evolved independently. In our model, one basic hypothesis is each In the time step, the gas falls exponentially on the galactic disk and is directly superimposed on the existing radial surface density profile, in which the index plate's standard length r_d is proportional to the product of the virial radius r_ (VIR) and the rotational parameter lambda of the dark matter halo of the galaxy. Our model uses two models describing the formation of molecular gases. Type: one is based on the analytical model of Krumholz et al. The proportion of molecular gas is related to the local density of gas and the local gas abundance; the other is the model related to the molecular gas ratio and interstellar pressure. According to the approximation of Obreschkow et al, the proportion of the molecular gas and the density of the gas surface and the density of the mass of the star As the stellar formation occurs in the interstellar macromolecular clouds, and according to the observations of Leroy et al., the star formation rate is approximately proportional to the surface density of the molecular gas, so we use the star formation law associated with the molecular gas surface density in the model.
【作者单位】：中国科学院上海天文台星系宇宙学重点实验室;
【分类号】：P152

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