在DEEP2星系红移巡天中来自紧密星系对的湿、干和混合星系合并的红移演化
The Redshift Evolution of Wet, Dry, and Mixed Galaxy Mergers from Close Galaxy Pairs in the DEEP2 Galaxy Redshift Survey
摘要：
利用从DEEP 2红移巡天中选取的运动学对，研究了不同类型星系的星系偶分数和合并率的红移演化。通过将对分数的演化参数化为（1+z）^{m}，我们发现对于所有的星系，当-21 < M_B^{e} <-19时，伴随率随红移的增加而适度增加，m = 0.41+-0.20。蓝色星系的蓝色伴星速率演化稍快，m = 1.27+-0.35，而红色星系过去的红色伴星较少，负斜率m = -0.92+-0.59就证明了这一点。我们发现，在低红移的对分数内的红色序列超过了蓝色的云，表明更高的合并概率之间的红色星系相比，蓝色星系。在进一步假设合并时间尺度和合并的星系对比例的情况下，0.1 < z <1.2的星系主要合并速率估计为~10^{-3}h^{3}Mpc^{-3}Gyr^{-1}，不确定性系数为2。在z ~ 1.1时，68%的合并是湿的，8%的合并是干的，24%的合并是混合的，而在z ~ 0.1时，31%的湿合并，25%的干合并和44%的混合合并。干合并率随红移减小而增加主要是由于红星系的同向运动数密度随时间增加。大约有22%到54%的现今L^{*}星系在z ~ 1.2之后经历过大合并，这取决于大合并的定义。此外，24%的红星系在本时代的干合并与光度比之间的1：4和4：1，因为z ~ 1。我们的研究结果还表明，湿合并和/或混合合并可能是产生中等质量的红星系的部分原因，而大规模的红星系的很大一部分是通过干合并组装在以后的时间。
英文摘要：
We study the redshift evolution of galaxy pair fractions and merger rates for different types of galaxies using kinematic pairs selected from the DEEP2 Redshift Survey. By parameterizing the evolution of the pair fraction as (1+z)^{m}, we find that the companion rate increases mildly with redshift with m = 0.41+-0.20 for all galaxies with -21 < M_B^{e} < -19. Blue galaxies show slightly faster evolution in the blue companion rate with m = 1.27+-0.35 while red galaxies have had fewer red companions in the past as evidenced by the negative slope m = -0.92+-0.59. We find that at low redshift the pair fraction within the red sequence exceeds that of the blue cloud, indicating a higher merger probability among red galaxies compared to that among the blue galaxies. With further assumptions on the merger timescale and the fraction of pairs that will merge, the galaxy major merger rates for 0.1 < z <1.2 are estimated to be ~10^{-3}h^{3}Mpc^{-3}Gyr^{-1} with a factor of 2 uncertainty. At z ~ 1.1, 68% of mergers are wet, 8% of mergers are dry, and 24% of mergers are mixed, compared to 31% wet mergers, 25% dry mergers, and 44% mixed mergers at z ~ 0.1. The growth of dry merger rates with decreasing redshift is mainly due to the increase in the co-moving number density of red galaxies over time. About 22% to 54% of present-day L^{*} galaxies have experienced major mergers since z ~ 1.2, depending on the definition of major mergers. Moreover, 24% of the red galaxies at the present epoch have had dry mergers with luminosity ratios between 1:4 and 4:1 since z ~ 1. Our results also suggest that the wet mergers and/or mixed mergers may be partially responsible for producing red galaxies with intermediate masses while a significant portion of massive red galaxies is assembled through dry mergers at later times.
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