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arXiv 1504.05604astro-ph.GAastro-ph.CO
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LoCuSS:星系团中恒星形成的缓慢淬灭和预处理的需要

LoCuSS: The slow quenching of star formation in cluster galaxies and the need for pre-processing

C. P. Haines, M. J. Pereira, G. P. Smith, E. Egami, A. Babul, A. Finoguenov, F. Ziparo, S. L. McGee, T. D. Rawle, N. Okabe, S. M. Moran

摘要:

利用宽视场Spitzer 24 μ m和GALEX NUV成像技术,结合星系团成员的高完整光谱,对30个质量为0.15<z<0.30的星系团中的恒星形成星系的空间分布和运动学进行了研究。恒星形成星系团的比例(f_SF)随着星系团中心半径的增加而稳步上升,到2 r200时增加了5倍,但即使在3r 200时仍远低于场值。这种在大半径下抑制恒星形成的现象不能被这样的模型所再现,即恒星形成只有在落入星系团的r200范围内才被淬灭,但这与其中一些星系团首先在星系团内进行预处理是一致的。尽管f_SF半径有增加的趋势,但恒星形成星系的表面密度实际上随着半径的增加而稳步下降,从核心下降约15倍到2 r200。这需要恒星形成在最近吸积的螺旋中存活2- 3 Gyr,以建立星团内恒星形成星系的明显过密度。在0.3r500处,成星星系群的速度色散曲线显示出一个1.44-sigma_v的尖峰,比不活跃星系团成员的速度色散曲线高出10- 35%,而在r500以内,它们的速度分布呈现出一个平顶曲线。所有这些结果都与恒星形成的星系团是一个下降的人口,但也必须生存约0.5- 2Gyr超过通过r200。通过比较观察到的分布在堆叠焦散图与千年模拟预测的恒星形成的星系,我们得到了一个最佳拟合模型,其中SFR指数下降淬火时间尺度为1.73 \pm 0.25 Gyr吸积成集群。

英文摘要:

We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15<z<0.30, combining wide-field Spitzer 24um and GALEX NUV imaging with highly-complete spectroscopy of cluster members. The fraction (f_SF) of star-forming cluster galaxies rises steadily with cluster-centric radius, increasing fivefold by 2r200, but remains well below field values even at 3r200. This suppression of star formation at large radii cannot be reproduced by models in which star formation is quenched in infalling field galaxies only once they pass within r200 of the cluster, but is consistent with some of them being first pre-processed within galaxy groups. Despite the increasing f_SF-radius trend, the surface density of star-forming galaxies actually declines steadily with radius, falling ~15x from the core to 2r200. This requires star-formation to survive within recently accreted spirals for 2--3Gyr to build up the apparent over-density of star-forming galaxies within clusters. The velocity dispersion profile of the star-forming galaxy population shows a sharp peak of 1.44-sigma_v at 0.3r500, and is 10--35% higher than that of the inactive cluster members at all cluster-centric radii, while their velocity distribution shows a flat, top-hat profile within r500. All of these results are consistent with star-forming cluster galaxies being an infalling population, but one that must also survive ~0.5--2Gyr beyond passing within r200. By comparing the observed distribution of star-forming galaxies in the stacked caustic diagram with predictions from the Millennium simulation, we obtain a best-fit model in which SFRs decline exponentially on quenching time-scales of 1.73\pm0.25 Gyr upon accretion into the cluster.

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