AGN反馈对发光星系冷却和恒星形成的调节及恒星形成起始的冷却时间/熵阈值
The Regulation of Cooling and Star Formation in Luminous Galaxies by AGN Feedback and the Cooling-Time/Entropy Threshold for the Onset of Star Formation
摘要：
利用宽波段光学成像和Chandra X射线数据，对46个团中央优势星系（CDG）的恒星形成、团内介质（ICM）和中央活动星系核（AGN）之间的关系进行了研究。我们发现，当热大气的中心冷却时间低于~ 5 × 10^8年，或者说当中心熵低于~ 30 keV·cm ^2时，恒星形成的起始点会出现一个非常明显的临界点。除了这个标准之外，在冷却流中的恒星形成似乎还需要X射线和星系的质心位于彼此的20 kpc以内，并且喷流（腔）功率小于X射线冷却光度。这三个标准，再加上我们样本中的冷却时间与活动星系核爆发（空腔）年龄的高比率，直接将CDG中恒星形成和活动星系核活动的存在与团内等离子体的冷却不稳定性联系起来。我们的研究结果提供了令人信服的证据，AGN反馈到热ICM在很大程度上负责调节冷却和恒星形成的核心集群，导致显着增长的超大质量黑洞在CDG在晚些时候。
英文摘要：
Using broadband optical imaging and Chandra X-ray data for a sample of 46 cluster central dominant galaxies (CDGs), we investigate the connection between star formation, the intracluster medium (ICM), and the central active galactic nucleus (AGN). We report the discovery of a remarkably sharp threshold for the onset of star formation that occurs when the central cooling time of the hot atmosphere falls below ~ 5x10^8 yr, or equivalently when the central entropy falls below ~ 30 keV cm^2. In addition to this criterion, star formation in cooling flows also appears to require that the X-ray and galaxy centroids lie within ~ 20 kpc of each other, and that the jet (cavity) power is smaller than the X-ray cooling luminosity. These three criteria, together with the high ratio of cooling time to AGN outburst (cavity) age across our sample, directly link the presence of star formation and AGN activity in CDGs to cooling instabilities in the intracluster plasma. Our results provide compelling evidence that AGN feedback into the hot ICM is largely responsible for regulating cooling and star formation in the cores of clusters, leading to the significant growth of supermassive black holes in CDGs at late times.
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