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arXiv 2106.02478astro-ph.GA
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鹰星系中气体燃料恒星形成的历史

History of the gas fuelling star formation in eagle galaxies

L. Scholz-Diaz, J. Sanchez Almeida, C. Dalla Vecchia

摘要:

理论预测,宇宙气体吸积在星系中恒星形成的过程中扮演着重要的角色。然而,在解释观测结果时仍然缺乏对吸积过程的详细描述。利用最先进的宇宙流体动力学模拟eagle,我们计算了由于吸积过程的随机性而在星系盘中产生的化学不均匀性。在低质量系统和大质量星系的外围,低金属丰度区域与增强的恒星形成有关,这一趋势在大质量星系的中心逆转。这些预测与MaNGA巡天观测到的本星系旋涡星系中恒星形成率面密度与金属丰度之间的关系相一致。然后,我们分析了在两个关键时期产生恒星的气体的起源,z simeq 0和z simeq 2。主要贡献来自于在恒星形成前约1 Gyr就已经存在于星系中的气体,其中一部分来自于外部气体,在高红移时更大。吸积的气体可能来自主要和次要的合并,但也可能是引力未结合的气体,以及来自与暗星系的合并(即,其中超过95%的重子质量处于气体中的晕)。我们给出了这些气体源的相对贡献作为恒星质量的函数(8 < log Mstar < 11)。即使在z = 0时,一些低质量星系在最后一个Gyr期间与暗星系合并,形成了其总恒星质量的重要部分。

英文摘要:

Theory predicts that cosmological gas accretion plays a fundamental role fuelling star formation in galaxies. However, a detailed description of the accretion process to be used when interpreting observations is still lacking. Using the state-of-the-art cosmological hydrodynamical simulation eagle, we work out the chemical inhomogeneities arising in the disk of galaxies due to the randomness of the accretion process. In low-mass systems and outskirts of massive galaxies, low metallicity regions are associated with enhanced star-formation, a trend that reverses in the centers of massive galaxies. These predictions agree with the relation between surface density of star formation rate and metallicity observed in the local spiral galaxies from the MaNGA survey. Then, we analyse the origin of the gas that produces stars at two key epochs, z simeq 0 and z simeq 2. The main contribution comes from gas already in the galaxy about 1 Gyr before stars are formed, with a share from external gas that is larger at high redshift. The accreted gas may come from major and minor mergers, but also as gravitationally unbound gas and from mergers with dark galaxies (i.e., haloes where more than 95 % of the baryon mass is in gas). We give the relative contribution of these sources of gas as a function of stellar mass (8 < log Mstar < 11). Even at z = 0, some low-mass galaxies form a significant fraction of their total stellar mass during the last Gyr from mergers with dark galaxies.

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