[论文解读] The WIRCAM Deep Infrared Cluster Survey I: Groups and Clusters at z > 1.1

R. M. Bielby, A. Finoguenov+13 more|arXiv (Cornell University)|Jul 29, 2010

Galaxies: Formation, Evolution, Phenomena参考文献 62被引用 33

一句话总结

本研究利用两片深空场中的XMM-Newton X射线、CFHTLS光学和WIRCam近红外数据，识别出15个红移z ≥ 1.1的星系群和星系团。观测到的星系团数量计数略低于WMAP 7年模型的预测，暗示与标准宇宙学可能存在张力，尽管检测极限和物理关系的不确定性使得尚无法得出明确结论。

ABSTRACT

We use a combination of CFHTLS deep optical data, WIRcam Deep Survey (WIRDS) near-infrared data and XMM-Newton survey data to identify z ≳ 1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to such clusters can not be identified without deep near-infrared data and as such the total of ≈1 deg2 of J, H and Ks band imaging provided by WIRDS is an indispensable tool in such work.
 
 Methods. Using public XMM X-ray data, we identify extended X-ray sources in the two fields. The resulting catalogue of extended X-ray sources was then analyzed for optical/near-infrared counterparts, using a red-sequence algorithm applied to the deep optical and near-infrared data. Redshifts of candidate groups and clusters were estimated using the median photometric redshifts of detected counterparts and where available these were combined with spectroscopic data (from VVDS deep and ultra-deep and using AAT AAOmega data). Additionally, we surveyed X-ray point sources for potential group systems at the limit of our detection range in the X-ray data. A catalogue of z > 1.1 cluster candidates in the two fields has been compiled and cluster masses, radii and temperatures have been estimated using the scaling relations.
 
 Results. The catalogue of group and cluster candidates consists of 15 z ≳ 1.1 objects. We find several massive clusters (M ≳ 1014 M⊙) and a number of lower mass clusters/groups. Three of the detections are previously published extended X-ray sources. Of note is JKSC 041 (previously detected via Chandra X-ray data and reported as a z = 1.9 cluster based on UKIDSS infrared imaging) for which we identify a number of structures at redshifts of z = 0.8, z = 0.96, z = 1.13 and z = 1.49 (but see no evidence of a structure at z = 1.9). We also make an independent detection of the massive cluster, XMMXCS J2215.9-1738, for which we estimate a redshift of z = 1.37 (compared to the spectroscopically confirmed redshift of z = 1.45). We use the z ≳ 1.1 catalogue to compare the cluster number counts in these fields with models based on WMAP 7-year cosmology and find that the models slightly over-predict the observations, whilst at z > 1.5 we do not detect any clusters. We note that cluster number counts at z ≳ 1.1 are highly sensitive to the cosmological model, however a significant reduction in present statistical (due to available survey area) and systematic (due to cluster scaling relations) uncertainties is required in order to confidently constrain cosmological parameters using cluster number counts at high redshift.

研究动机与目标

• 利用多波段数据识别并表征红移z ≥ 1.1的星系群和星系团。
• 评估观测到的高红移星系团数量计数与WMAP 7年宇宙学模型预测的一致性。
• 评估检测极限和星系团物理关系的不确定性对高红移星系团计数所施加的宇宙学约束的影响。
• 通过结合X射线探测与红序列分析，提高高红移星系团巡天的可靠性。

提出的方法

• 将XMM-Newton X射线数据与深空光学（CFHTLS）和近红外（WIRCam）图像相结合，以探测扩展X射线源。
• 应用红序列算法，在光学和近红外数据中识别潜在的星系团对应体。
• 利用检测到的成员星系的中位红移估计光谱红移，辅以VVDS和AAT/AAOmega的光谱红移数据。
• 利用X射线光度与温度的物理关系估算星系团的质量、半径和温度。
• 根据检测置信度（标记）对候选体进行分类，包括非可靠检测（标记=5），以评估巡天的完备性。
• 将观测到的星系团数量计数与WMAP 7年宇宙学模型预测进行比较，同时考虑巡天几何形状和检测效率。

实验结果

研究问题

• RQ1 在CFHTLS D1和D4场中，利用多波段数据可探测到多少个红移z ≥ 1.1的星系群和星系团？
• RQ2 观测到的z ≥ 1.1星系团数量计数在多大程度上与WMAP 7年宇宙学模型的预测一致？
• RQ3 检测极限和星系团物理关系的不确定性如何影响基于高红移星系团计数的宇宙学约束？
• RQ4 包含非可靠星系团候选体（如标记=5）对观测与模型之间星系团数量计数一致性的影响如何？

主要发现

• 本巡天共识别出15个红移z ≥ 1.1的星系群和星系团，其中包括三个此前已发表的扩展X射线源。
• 其中三个检测结果（包括JKSC 041）显示出z = 0.8、0.96、1.13和1.49的多重结构，但未发现此前推测的z = 1.9处的结构证据。
• 对XMMXCS J2215.9-1738的独立探测得到其光谱红移估计为z = 1.37，而光谱确认的红移为z = 1.45。
• 观测到的z ≥ 1.1星系团数量计数略低于WMAP 7年模型预测，暗示可能与标准宇宙学存在张力。
• 包含非可靠候选体（标记=5）后，观测计数与WMAP 7年模型的吻合度提高，表明这些候选体可能包含真实与虚假检测的混合。
• 只有在包含标记=5候选体时，z > 1.1星系团的光度函数才与WMAP 7年模型预测良好一致，凸显了物理关系和检测极限中系统性不确定性的关键作用。