M33的演化和恒星形成历史研究

发布时间：2018-02-24 03:14

本文关键词： 星系化学-颜色演化恒星形成历史 M33　出处：《中国科学院研究生院（云南天文台）》2012年硕士论文　论文类型：学位论文

【摘要】：M33(NGC598)是本星系群中最小的旋涡星系，其重子物质质量仅约为银河系的十分之一，中心无显著核球，旋臂结构较为完整，在其演化历史中没有并合和其它相互作用的迹象。由于它适当的距离和角直径以及相对较小的倾角，使得气体和星族的径向分布观测成为可能，从理论上对它进行详细研究，有利于我们进一步理解小质量旋涡星系的形成及演化过程。唯象模型被广泛应用于本星系群中银河系等旋涡星系的化学演化研究中，在理解这些星系的演化方面取得了一定的进展，但之前的模型仍然有一些不足之处，其主要包括以下几个方面：(I)没有分开计算分子氢气体和原子氢气体；(II)采用的恒星形成律与总的气体面密度相关；(III)没有考虑外流。然而，这些因素直接影响到星系的演化历史。首先，分子氢气体和原子氢气体对于星系中发生各个物理过程至关重要，并且近年来星系中分子氢和原子氢等冷气体成分的观测数据逐渐增多，所以有必要分开计算分子氢气体和原子氢气体来严格约束模型。其次，由于恒星形成于巨分子云中，所以恒星形成律应该与分子氢气体面密度更相关。最后，M33是小质量的旋涡星系，，势阱浅，容易受到超新星爆发等因素的影响而引发外流，故外流必不可少。为了解决以上问题，以银河系的化学演化模型为参照，我们重新构建了盘状星系M33形成和演化的化学-颜色演化模型，在模型中同时考虑了气体内落和外流的影响，分开计算了星系盘中分子气体和原子气体成分，使用了与分子氢气体面密度相关的恒星形成律。其中内落采用了吸积模型的形式来描述星系盘的增长过程，而外流速率与恒星形成率成正比；星系盘中分子气体和原子气体成分的物理模型使用了分子气体比例与星际压强相关的模型来描述分子氢气体与原子氢气体的转换；恒星形成律采用了Leroy et al.(2008)[1]的与分子氢气体面密度成正比的恒星形成律来描述冷气体转化为恒星的速率。模型中引入两个自由参数：内落时标τ和外流效率bout。利用我们建立的模型，详细计算了M33盘的分子氢气体、原子氢气体、总气体、SFR、O元素丰度、FUV波段和K波段的表面亮度及FUV K颜色等参量的径向轮廓，通过将模型预言与近年来的观测结果进行比较，从而进一步理解星系盘的恒星形成历史的主要特征。得出了如下结论：(i) M33的恒星形成效率比Leroy et al.(2008)[1]的较大质量的近邻旋涡星系的平均值大，这点与前人的观测结果一致；(ii) M33是通过原初气体内落逐渐形成的，并且模型预言的结果对内落时标很敏感，内落时标越长，分子氢、原子氢及总气体面密度和SFR越高，颜色越蓝，金属丰度越低，而外流主要影响盘的金属丰度；(iii)当模型采用较为适中的外流效率和“由内到外”的形成图像时，模型预言的结果能够很好地重现M33的大部分观测特征；(iv)与经典的K-S SF Law相比，与分子氢气体面密度相关的SF-Law将更适合于描述盘星系的演化，特别是冷气体及星族的径向面密度分布。
[Abstract]:M33 (NGC598) is the smallest spiral galaxy in the local group, the baryon mass is only about 1/10 of the Milky Way center, no significant nuclear ball arm structure is complete, in its evolutionary history and no interaction and other signs. Because of its proper distance and angle and diameter is relatively small the angle that the radial distribution of gas and stars can be observed, detailed research on it from theory, conducive to further our understanding of the formation and evolution process of small mass of spiral galaxies.
Study on the chemical evolution of the phenomenological model has been widely applied in the Milky Way this galaxy group series of spiral galaxies, some progress has been made in understanding the evolution of these galaxies, but before the model still has some shortcomings, which include the following: (I) there is no separate calculation of molecular and atomic hydrogen gas hydrogen gas; (II) the star formation law and the total gas surface density; (III) does not consider the outflow. However, these factors directly affect the evolution of galaxies. Firstly, molecular hydrogen gas and hydrogen gas is essential for various physical processes in galaxies, and the observation data of cold gas in recent years the galaxy in molecular hydrogen and hydrogen atoms were gradually increased, so it is necessary to separate the calculation of molecular hydrogen gas and atomic hydrogen gas to strict constraint model. Secondly, the star formation in the giant molecular cloud The law of star formation should be more related to the surface density of molecular hydrogen. Finally, M33 is a small mass spiral galaxy with shallow potential and outflow due to the influence of supernovae and other factors. Therefore, the outflow is essential.
In order to solve the above problems, according to the Milky Way Department of chemical evolution model, we constructed M33 disk galaxy formation and evolution of the chemical evolution of color model, the model takes into account the gas infall and outflow, the galactic disk of molecular gas and atom gas components separately, the formation of the use of the relevant law with the molecular gas density in the decent stars. The falling accretion model to describe the growth process of the galactic disk, and the outflow rate and the rate of star formation is proportional to the physical model of galaxies; conversion of molecular gas and atomic gas components used to model gas molecules associated with the proportion of interstellar pressure to describe the molecular hydrogen gas and atomic hydrogen gas; star formation law by Leroy et al. (2008) [1] stars with molecular hydrogen gas surface density is proportional to the formation of law to describe the cold gas into Star rate. The introduction of two free parameters in the model: in the fall when the standard tau and outflow efficiency of bout.
Using our model, molecular hydrogen gas M33 disk is calculated in detail, atomic hydrogen gas, total gas, SFR, O element abundances, the radial profile of FUV band and K band FUV K color surface brightness and other parameters, the model predicted results are compared with observations in recent years, in order to further understand the formation the main feature of the history of the Galactic disc stars. Conclusions are drawn as follows: (I) M33 star formation efficiency than Leroy (2008) et al. [1] of the neighboring spiral galaxies average, this observation results agree with previous results; (II) M33 is the primordial gas in falling gradually, and the results predicted by the model is very sensitive to the fall time scale, fall time scale is longer, molecular hydrogen, hydrogen atoms and total gas density and the higher the decent SFR, color is blue, the metallicity is lower, and the outflow of main influence disc metal abundance; (III) when using model A more modest outflow rate and formation of the "image from the inside to the outside", most of the features observed results predicted by the model can well reproduce the M33; (IV) compared with the classical K-S SF Law evolution related to molecular hydrogen decent density of SF-Law will be more suitable for describing disc galaxies, especially radial the surface density distribution of cold gas and stars.

【学位授予单位】：中国科学院研究生院（云南天文台）
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：P152

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