追踪造成宇宙6 - 8 keV背景的源星族
Tracking Down the Source Population Responsible for the Unresolved Cosmic 6-8 keV Background
摘要：
使用4 Ms Chandra Deep Field-South（CDF-S）巡天，我们已经确定了6845个X射线未探测星系的样本，这些星系占6 - 8 keV宇宙X射线背景（XRB）未分辨的~20 - 25%。该样本是通过对来自父目录的源应用质量和颜色切割来构建的，该父目录基于4 Ms CDF-S的中心6 '半径区域的GOODS-South HST z波段成像。堆叠的6 - 8 keV检测在3.9 sigma水平是显着的，但在4 - 6 keV波段没有检测到堆叠的发射，这表明存在一个潜在的人口高度模糊的活动星系核（AGN）。对这6845个星系的进一步研究表明，位于蓝云顶部的红移为1 <z <3，星等为25 <z_850 <28，恒星质量为2E8 <M_star/M_sun <2E9的星系对未分辨的6 - 8 keV XRB有很大贡献。这样的人口似乎是令人惊讶的，因为大多数X射线探测到的活动星系核居住在大质量（>~1E10 M_sun）星系。我们讨论了这个基本的活动星系核人口的限制，支持相对低质量的星系主办高度模糊的活动星系核的证据，并进一步提高堆叠信号的前景。
英文摘要：
Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray undetected galaxies that dominates the unresolved ~ 20-25% of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South HST z-band imaging of the central 6'-radius area of the 4 Ms CDF-S. The stacked 6-8 keV detection is significant at the 3.9 sigma level, but the stacked emission was not detected in the 4-6 keV band which indicates the existence of an underlying population of highly obscured active galactic nuclei (AGNs). Further examinations of these 6845 galaxies indicate that the galaxies on the top of the blue cloud and with redshifts of 1 < z < 3, magnitudes of 25 < z_850 < 28, and stellar masses of 2E8 < M_star/M_sun < 2E9 make the majority contributions to the unresolved 6-8 keV XRB. Such a population is seemingly surprising given that the majority of the X-ray detected AGNs reside in massive (> ~1E10 M_sun) galaxies. We discuss constraints upon this underlying AGN population, supporting evidence for relatively low-mass galaxies hosting highly obscured AGNs, and prospects for further boosting the stacked signal.
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