CFHTLenS: Improving the quality of photometric redshifts with precision photometry
CFHTLenS: Improving the quality of photometric redshifts with precision photometry
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DOI：
10.1111/j.1365-2966.2012.20468.x
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发表时间：
2011-11
影响因子：
4.8
通讯作者：
H. Hildebrandt;T. Erben;K. Kuijken;L. Waerbeke;C. Heymans;J. Coupon;J. Benjamin;C. Bonnett
中科院分区：
文献类型：
--
作者：
H. Hildebrandt;T. Erben;K. Kuijken;L. Waerbeke;C. Heymans;J. Coupon;J. Benjamin;C. Bonnett
在这里，我们介绍了从广域成像数据测量准确颜色和光度红移(Photo-z‘s)的各种方法的结果。我们使用了来自加拿大-法国-夏威夷-望远镜遗产调查(CFHTLS)的数据，这些数据已经由CFHTLenS(CFHTLenS)团队重新处理，以开展一些弱引力透镜研究。着重讨论了对五个光学波段不同点扩展函数(PSF)引起的系统效应的校正。讨论了校正这些影响的不同方法，并通过将照片Z与大的光谱红移(SPEC-Z)数据集进行比较来量化所产生的照片Z的精度。对不同波段的PSF进行仔细的均化处理，提高了照片z的整体精度。在星系较小、通量测量受PSF效应影响较大的较暗星系中，这种增益尤其明显。我们还研究了在已知SPEC-Z星系的帮助下重新校准光度学零点(ZPs)的可能性。我们发现，如果适当地考虑PSF效应，ZPS的重新校准就变得不那么重要了，这表明文献中描述的以前的这种重新校准实际上可能主要是对PSF效应的校正，而不是对ZPS中实际不准确的校正。这一发现对未来的调查，如儿童，DES，LSST，或欧几里德的影响是复杂的。一方面，用SPEC-Z重新校准ZP可能不像之前想象的那样准确。另一方面，仔细的PSF均化可能会提供一条出路，并在不需要完全光谱覆盖的情况下产生准确、均匀的光度测量。这是描述CFHTLenS技术方面的系列文章中的第一篇。(节选)
Here we present the results of various approaches to measure accurate colours and photometric redshifts (photo-z’s) from wide-field imaging data. We use data from the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS) which have been re- processed by the CFHT Lensing Survey (CFHTLenS) team in order to carry out a number of weak gravitational lensing studies. An emphasis is put on the correction of systematic effects in the photo-z’s arising from the different Point Spread Functions (PSF) in the five optical bands. Different ways of correcting these effects are discussed and the resulting photo-z accuracies are quantified by comparing the photo-z’s to large spectroscopic redshift (spec-z) data sets. Careful homogenisation of the PSF between bands leads to increased overall accuracy of photo-z’s. The gain is particularly pronounced at fainter magnitudes where galaxies are smaller and flux measurements are affected more by PSF-effects. We also study possible re- calibrations of the photometric zeropoints (ZPs) with the help of galaxies with known spec-z’s. We find that if PSF-effects are properly taken into account, a re-calibration of the ZPs becomes much less important suggesting that previous such re-calibrations described in the literature could in fact be mostly corrections for PSF-effects rather than corrections for real inaccuracies in the ZPs. The implications of this finding for future surveys like KiDS, DES, LSST, or Euclid are mixed. On the one hand, ZP re-calibrations with spec-z’s might not be as accurate as previously thought. On the other hand, careful PSF homogenisation might provide a way out and yield accurate, homogeneous photometry without the need for full spectroscopic coverage. This is the first paper in a series describing the technical aspects of CFHTLenS. (abridged)