Evidence for recent star formation in BCGs : A correspondence between blue cores and UV excess
Evidence for recent star formation in BCGs : A correspondence between blue cores and UV excess
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BCG 中近期恒星形成的证据：蓝色核心与紫外线过量之间的对应关系
DOI：
10.1111/j.1365-2966.2009.14534.x
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发表时间：
2008
影响因子：
4.8
通讯作者：
Canada.
中科院分区：
文献类型：
--
作者：
A. Pipino;S. K. C. Bildfell;A. Babul;H. H. J. S. Astrophysics;U. Oxford;UK.;D. PhysicsAstronomy;U. Victoria;Canada.
我们对GALEX任务的近紫外（NUV）数据和加拿大星团比较项目中7个最亮星团星系（bcg）样本的（光学）颜色概况进行了联合分析。我们发现，每一个具有蓝色静止框UV颜色的BCG在其光学颜色配置文件中也显示出蓝核。相反，缺少蓝色核心的bcg，呈现出单调的颜色梯度，是典型的古老椭圆星系，在紫外线下是红色的。我们将此解释为蓝色BCGs中NUV增强是由最近的恒星形成驱动的证据，而不是来自古老进化的恒星群，如水平分支恒星。此外，紫外增强不可能来自AGN，因为蓝色核心的空间范围明显大于可能由大质量黑洞引起的污染区域。蓝色BCGs中最近形成的恒星的年龄通常小于200myr，质量分数也不到1%。虽然这里研究的样本很小，但我们首次证明了椭圆星系（特别是BCGs）的蓝色核心与GALEX观测到的nuv增强之间的一对一对应关系。这种一对一的对应关系和最近恒星形成的持续年轻的年龄，再加上与主星团的x射线特性的额外相关性，强烈表明恒星形成是由星团内介质冷却的气体推动的。反过来，这意味着在大质量星团中，任何AGN对星团内介质的加热只会降低冷却流的强度，而一旦冷却流开始，它几乎总是活跃的。总的来说，这些结果表明，AGN反馈在当今的BCGs中虽然重要，但并不像De Lucia等人（2006）提出的最新理论模型所表明的那样有效。
We present a joint analysis of near-ultraviolet (NUV) data from the GALEX mission and (optical) colour profiles for a sample of 7 Brightest Cluster Galaxies (BCGs) in the Canadian Cluster Comparison Project. We find that every BCG which has a blue rest-frame UV colour also shows a blue-core in its optical colour profile. Conversely, BCGs that lack blue cores and show monotonic colour gradients typical of old elliptical galaxies, are red in the UV. We interpret this as evidence that the NUV enhancement in the blue BCGs is driven by recent star formation and not from old evolved stellar populations such as horizontal branch stars. Furthermore, the UV enhancement cannot be from an AGN because the spatial extent of the blue cores is significantly larger than the possible contamination region due to a massive black hole. The recent star formation in the blue BCGs typically has an age less than 200 Myrs and contributes mass fractions of less than a percent. Although the sample studied here is small, we demonstrate, for the first time, a one-to-one correspondence between blue cores in elliptical galaxies (in particular BCGs) and a NUV-enhancement observed using GALEX. The combination of this one-to-one correspondence and the consistently young age of recent star formation, coupled with additional correlations with the host cluster’s X-ray properties, strongly suggests that the star formation is fueled by gas cooling out of the intracluster medium. In turn, this implies that any AGN heating of the intracluster medium in massive clusters only acts to reduce the magnitude of the cooling flow and that once this flow starts, it is nearly always active. Collectively, these results suggest that AGN feedback in present-day BCGs, while important, cannot be as efficient as suggested by the recent theoretical model by proposed by De Lucia et al. (2006).