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首页> 外文期刊>PASJ: Publications of the Astronomical Society of Japan >Properties of molecular gas in galaxies in the early and mid stages of interaction. II. Molecular gas fraction
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Properties of molecular gas in galaxies in the early and mid stages of interaction. II. Molecular gas fraction

机译：相互作用初期和中期星系中分子气体的性质。二。分子气体分数

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We have investigated properties of the interstellar medium in interacting galaxies in early and mid stages using mapping data of 12CO(J = 1–0) and H?i. Assuming the standard CO–H2 conversion factor, we found no difference in molecular gas mass, atomic gas mass, and total gas mass (the sum of atomic and molecular gas mass) between interacting galaxies and isolated galaxies. However, interacting galaxies have a higher global molecular gas fraction $$f_{m {mol}}^{m {global}}$$ (the ratio of molecular gas mass to total gas mass averaged over a whole galaxy) at 0.71?±?0.15 than isolated galaxies (0.52?±?0.18). The distribution of the local molecular gas fraction fmol, the ratio of the surface density of molecular gas to that of the total gas, is different from the distribution in typical isolated galaxies. By a pixel-to-pixel comparison, isolated spiral galaxies show a gradual increase in fmol along the surface density of total gas until it is saturated at 1.0, while interacting galaxies show no clear relation. We performed pixel-to-pixel theoretical model fits by varying metallicity and external pressure. According to the model fitting, external pressure can explain the trend of fmol in the interacting galaxies. Assuming half of the standard CO–H2 conversion factor for interacting galaxies, the results of pixel-to-pixel theoretical model fitting get worse than adopting the standard conversion factor, although $$f_{m {mol}}^{m {global}}$$ of interacting galaxies (0.62?±?0.17) becomes the same as in isolated galaxies. We conclude that external pressure occurs due to the shock prevailing over a whole galaxy or due to collisions between giant molecular clouds even in the early stage of the interaction. The external pressure accelerates an efficient transition from atomic gas to molecular gas. Regarding the chemical timescale, high fmol can be achieved at the very early stage of interaction even if the shock induced by the collision of galaxies ionizes interstellar gas.
机译：我们使用12CO（J = 1-0）和H？i的映射数据研究了星系间介质在相互作用星系的早期和中期的特性。假设标准的CO–H2转换因子，我们发现相互作用的星系和孤立的星系之间的分子气体质量，原子气体质量和总气体质量（原子和分子气体质量之和）没有差异。但是，相互作用的星系具有较高的全局分子气体分数$$ f _ { rm {mol}} ^ { rm {global}} $$（整个星系中平均分子气体质量与总气体质量之比），值为0.71与孤立星系（0.52±0.18）相比，α±0.15。局部分子气体分数fmol的分布（分子气体的表面密度与总气体的表面密度之比）与典型的孤立星系中的分布不同。通过像素间的比较，孤立的螺旋星系显示fmol沿着总气体的表面密度逐渐增加，直到它达到1.0饱和为止，而相互作用的星系则没有明确的关系。我们通过改变金属性和外部压力来进行像素对像素的理论模型拟合。根据模型拟合，外部压力可以解释fmol在相互作用星系中的趋势。假设相互作用星系的标准CO-H2转换因子为一半，尽管$$ f _ { rm {mol}} ^ { rm {全局}} $$相互作用的星系（0.62？±？0.17）与孤立的星系相同。我们得出的结论是，外部压力是由于整个银河系中普遍存在的激波或由于巨大分子云之间的碰撞而产生的，即使在相互作用的早期也是如此。外部压力加速了从原子气体到分子气体的有效过渡。关于化学时间尺度，即使星系碰撞引起的震动使星际气体电离，也可以在相互作用的早期就获得较高的fmol。

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