The Infrared Counterparts of the Optically Unidentified Chandra Deep Field-South 1 Ms Sources
The Infrared Counterparts of the Optically Unidentified Chandra Deep Field-South 1 Ms Sources
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光学上无法识别的钱德拉深空南 1 Ms 源的红外对应物
DOI：
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发表时间：
2002
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通讯作者：
W. Keel
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作者：
Haojing Yan;R. Windhorst;H. Röttgering;S. Cohen;S. Odewahn;S. Chapman;W. Keel
Chandra Deep Field-South（CDF-S）1 Ms曝光产生了346个X射线源的目录，其中59个在甚大望远镜（VLT）/FORS 1和ESO-MPI/WFI深R波段图像上不可见，限制为Rvega = 26.1-26.7 mag. Using the first release of ESO VLT/ISAAC JHKs data on CDF-S，我们确定了12个这样的物体中的6个在这些红外观测的覆盖范围内。VLT/FORS 1 I波段数据进一步证实，这六个物体中有五个在光学上未被探测到。这六个同行的光度特性进行了比较，对那些在同一领域的钱德拉源的光学明亮的同行。我们发现这些光学亮的钱德拉源在近红外色空间中的位置是分叉的，其中一个分支的颜色与0 ≤ z ≤ 1.5的E/S 0星系的颜色一致，另一个分支的颜色与0 ≤ z ≤ 3.5的未红化活动星系核/类星体（AGN/QSO）的颜色一致。我们发现的6个对应星系似乎位于E/S 0分支及其延伸部分，这表明这些X射线源宿主大多是亮度为1 ≤ z ≤ 2.5的E/S 0星系（AB系统中MV ~ -20等）。另一方面，如果允许一定范围内的内消光（AV = 0-1等），则在很宽的红移范围内（0 ≤ z ≤ 5），其中一些也可以用活动星系核/类星体来解释。然而，后一种解释需要对这些天体的消光和红移进行微调。如果它们确实是活动星系核/类星体，那么其中最明亮的一颗就勉强够资格成为类星体。最后，我们指出，无论是高红移（z > 5）的恒星形成星系还是低红移的不规则星系都不能对这六个对应星系的性质做出可行的解释。
The Chandra Deep Field-South (CDF-S) 1 Ms exposure produced a catalog of 346 X-ray sources, of which 59 were not visible on the Very Large Telescope (VLT)/FORS1 and the ESO-MPI/WFI deep R-band images to a limit of Rvega = 26.1-26.7 mag. Using the first release of the ESO VLT/ISAAC JHKs data on the CDF-S, we identified six of the 12 such objects that were within the coverage of these IR observations. The VLT/FORS1 I-band data further confirm that five of these six objects are undetected in the optical. The photometric properties of these six counterparts are compared against those of the optically brighter counterparts of Chandra sources in the same field. We found that the location of these optically brighter Chandra sources in the near-IR color space was bifurcated, with the color of one branch being consistent with that of E/S0 galaxies at 0 ≤ z ≤ 1.5, and the other branch being consistent with that of unreddened active galactic nuclei/quasi-stellar objects (AGNs/QSOs) at 0 ≤ z ≤ 3.5. The six counterparts that we identified seemed to lie on the E/S0 branch and its extension, suggesting that these X-ray source hosts are mostly luminous E/S0 galaxies (MV ~ -20 mag in the AB system) at 1 ≤ z ≤ 2.5. On the other hand, some of them can also be explained by AGNs/QSOs over a wide redshift range (0 ≤ z ≤ 5), if a range of internal extinction (AV = 0-1 mag) is allowed. However, the later interpretation requires fine-tuning extinction together with redshift for these objects individually. If they are indeed AGNs/QSOs, the most luminous of them is just barely qualified for being a QSO. Finally, we point out that neither high-redshift (z > 5) star-forming galaxies nor irregular galaxies at lower redshift can be a viable explanation to the nature of these six counterparts.