大大质量星系的尺度演化研究进展

Research Progress on Size Evolution of Massive Galaxies

星系(恒星质量M_*>10^(10)M_⊙)的尺度(re)与M*之间有着明显的re_∝Mα_*关系。已有的研究揭示晚型星系(LTGs)和早型星系(ETGs)的α值分别对应0.22±0.03和0.75±0.05。另外,星系的尺度r_e与红移z之间存在演化关系:re_∝(1+z)~β。对于z<3的ETGs来说,它们在静止光学波段的尺度随时间生长的指数β=-1.5～-1.2,其在LTGs中对应β=-0.8～-0.6。介绍了星系形成理论模型,星系尺度的测量,星系恒星质量与星系尺度之间的关系,不同类型星系的尺度演化,以及阐述了该领域未来的研究方向。

The formation and evolution of massive galaxies （M＊ 〉 10^10M ） are hot topics in observational astronomy. Galaxies in the local universe present a bimodal distribution of colors, as introduced by the previous literature： the ＂Red Sequence＂ （RS）, which is mainly composed of Early-Type Galaxies （ETGs） with older stellar populations, and the ＂Blue Cloud＂ （BC）, which is composed of Late-Type Galaxies （LTGs） with extended structures. The bimodal distribution of colors of galaxies is confirmed to exist already at z = 2 - 3. Moreover, the remarkably tight mass-size correlation of galaxies has been confirmed （re e（ My）. At all redshifts the slope of the mass-size relation is shallow, α = 0.22±0.03, for LTGs with M. 〉 10^10M, and steep, α = 0.75 ±0.05, for ETGs with M. 〉 10^10M . Massive galaxies at high redshift have been observed to have properties which can be quite different from their counterparts at similar mass in the local universe. One of the most striking differences is the much smaller sizes observed for high-z galaxies. High-z ETGs （LTGs） are 3 0- 5 （2 - 4） times smaller than local ETGs （LTGs） with comparable mass. The average sizes of galaxies at fixed stellar mass show prominent evolutionary treads （re ∝（1 ＋ z）β）, with fast evolution for ETGs at 0 〈 z 〈 3, β = -1.5 ～ -1.2, and moderate evolution for LTGs at 0 〈 z 〈 3, β = -0.8 ～-0.6. Physical mechanisms have been proposed to explain the smaller size at high redshift and the resulting size evolution, such as major merger, dissipationless （dry） minor merger, progenitor bias, and ＂puff-up＂ due to the gas mass loss by active galactic nucleus （AGN） or supernova feedback.