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The Swift X-ray Telescope Cluster Survey - II. X-ray spectral analysis

机译：迅捷X射线望远镜群集调查-II。 X射线光谱分析

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Aims. We present a spectral analysis of a new, flux-limited sample of 72 X-ray selected clusters of galaxies identified with the X-ray Telescope (XRT) on board the Swift satellite down to a flux limit of ~10-14 erg?s-1?cm-2 (SWXCS). We carry out a detailed X-ray spectral analysis with the twofold aim of measuring redshifts and characterizing the properties of the intracluster medium (ICM) for the majority of the SWXCS sources. Methods. Optical counterparts and spectroscopic or photometric redshifts for some of the sources are obtained with a cross-correlation with the NASA/IPAC Extragalactic Database. Additional photometric redshifts are computed with a dedicated follow-up program with the Telescopio Nazionale Galileo and a cross-correlation with the SDSS. In addition, we also blindly search for the Hydrogen-like and He-like iron Kα emission line complex in the X-ray spectrum. We detect the iron emission lines in 35% of the sample, and hence obtain a robust measure of the X-ray redshift zX with typical rms error 1–5%. We use zX whenever the optical redshift is not available. Finally, for all the sources with measured redshift, background-subtracted spectra are fitted with a single-temperature mekal model to measure global temperature, X-ray luminosity and iron abundance of the ICM. We perform extensive spectral simulations to accounts for fitting bias, and to assess the robustness of our results. We derive a criterion to select reliable best-fit models and an empirical formula to account for fitting bias. The bias-corrected values are then used to investigate the scaling properties of the X-ray observables. Results. Overall, we are able to characterize the ICM of 46 sources with redshifts (64% of the sample). The sample is mostly constituted by clusters with temperatures between 3 and 10 keV, plus 14 low-mass clusters and groups with temperatures below 3 keV. The redshift distribution peaks around z ~ 0.25 and extends up to z ~ 1, with 60% of the sample at 0.1 < z < 0.4. We derive the luminosity?temperature relation for these 46 sources, finding good agreement with previous studies. Conclusions. Thanks to the good X-ray spectral quality and the low background of Swift/XRT, we are able to measure ICM temperatures and X-ray luminosities for the 46 sources with redshifts. Once redshifts are available for the remaining 26 sources, this sample will constitute a well-characterized, flux-limited catalog of clusters distributed over a broad redshift range (0.1 ≤ z ≤ 1.0) providing a statistically complete view of the cluster population with a selection function that allows a proper treatment of any measurement bias. The quality of the SWXCS sample is comparable to other samples available in the literature and obtained with much larger X-ray telescopes. Our results have interesting implications for the design of future X-ray survey telescopes, characterized by good-quality PSF over the entire field of view and low background.
机译：目的我们对由Swift卫星上的X射线望远镜（XRT）识别的72个X射线选定星系团进行了通量受限的新样品的光谱分析，其通量极限为〜10-14 erg？s -1？cm-2（SWXCS）。我们进行了详细的X射线光谱分析，其双重目的是测量大多数SWXCS源的红移并表征集群内介质（ICM）的特性。方法。通过与NASA / IPAC银河系外数据库互相关，可以获得某些光源的光学对应物和光谱或光度红移。使用Telescopio Nazionale Galileo的专用后续程序以及与SDSS的互相关性，可以计算其他光度红移。此外，我们还盲目地寻找X射线光谱中的类氢和类He铁Kα发射线络合物。我们检测了35％的样品中的铁发射线，因此获得了具有典型rms误差1-5％的X射线红移zX的可靠度量。每当光学红移不可用时，我们就使用zX。最后，对于所有具有测得的红移的源，将扣除背景的光谱与单温度麦克尔模型拟合，以测量ICM的整体温度，X射线发光度和铁丰度。我们进行了广泛的光谱模拟，以说明拟合偏差，并评估结果的稳健性。我们推导了选择可靠的最佳拟合模型的准则，以及计算拟合偏差的经验公式。然后，使用偏差校正后的值来调查X射线可观察对象的缩放比例属性。结果。总的来说，我们能够用红移（样本的64％）来表征46个源的ICM。样品主要由温度在3到10 keV之间的簇组成，加上14个温度在3 keV以下的低质量簇和组。红移分布在z〜0.25附近达到峰值，并一直扩展到z〜1，其中60％的样本位于0.1

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