More than half of the sources identified by recent radio sky surveys have not been detected by wide-field optical surveys. We present a study based on our co-added image stacking technique, in which our aim is to detect the optical emission from unresolved, isolated radio sources of the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey that have no identified optical counterparts in the Sloan Digital Sky Survey (SDSS) Stripe 82 co-added data set. From the FIRST catalogue, 2116 such radio point sources were selected, and cut-out images, centred on the FIRST coordinates, were generated from the Stripe 82 images. The already co-added cut-outs were stacked once again to obtain images of high signal-to-noise ratio, in the hope that optical emission from the radio sources would become detectable. Multiple stacks were generated, based on the radio luminosity of the point sources. The resulting stacked images show central peaks similar to point sources. The peaks have very red colours with steep optical spectral energy distributions. We have found that the optical spectral index alpha_nu falls in the range -2.9 < alpha_nu < -2.2, depending only weakly on the radio flux. The total integration times of the stacks are between 270 and 300 h, and the corresponding 5 sigma detection limit is estimated to be about m_r = 26.6 mag. We argue that the detected light is mainly from the central regions of dust-reddened Type 1 active galactic nuclei. Dust-reddened quasars might represent an early phase of quasar evolution, and thus they can also give us an insight into the formation of massive galaxies. The data used in the paper are available on-line at http://www.vo.elte.hu/doublestacking.
Simulations of the cosmic infrared and submillimeter background for future large surveys: II. Removing the low-redshift contribution to the anisotropies using stacking
How not to obtain the redshift distribution from probabilistic redshift estimates: Under what conditions is it not inappropriate to estimate the redshift distribution N(z) by stacking photo-z PDFs?
Radio-Selected Quasars in the Sloan Digital Sky Survey
我们结合第一次射电巡天和SDSS对z>3.5的类星体进行了一次试点巡天。虽然SDSS已经将光谱学的FIRST源作为类星体候选者，但我们的调查包括更暗的类星体，并通过使用严格的天体测量标准来匹配无线电和光学位置，大大提高了发现率。我们的方法允许选择高红移类星体的颜色偏差比光学选择，因为使用无线电选择基本上消除了恒星污染。我们报告了45个候选者的光谱结果，其中包括29个在0.37 < z < 5.2范围内的类星体，其中7个红移z>3.5。我们比较了使用无线电和光学标准选择的类星体，发现无线电选择的类星体具有更高比例的中度红化物体。我们导出了一个射电噪类星体在3.5<z<4.0处的光度函数，发现它与先前SDSS结果的预期吻合得很好。
First results on the cluster galaxy population from the Subaru Hyper Suprime-Cam survey. II. Faint end color-magnitude diagrams and radial profiles of red and blue galaxies at $0.1<z<1.1$
The Star Formation and Nuclear Accretion Histories of Normal Galaxies in the AGES Survey
我们结合了来自重叠的9.3平方度NOAO深宽视场巡天（NDWFS），AGN和星系演化巡天（AGES）以及XBootes巡天的IR，光学和X射线数据，以测量6146个正常星系的X射线演化，作为绝对光学光度，红移和光谱类型的函数，在很大程度上未探索的红移范围0.1 < z < 0.5。因为只有最近或最亮的星系在X射线中被单独检测到，我们使用叠加分析来确定样本的平均属性。我们的研究结果表明，光谱晚型星系的X射线辐射主要是由恒星形成，而从早型星系的主要是由热气体和活动星系核发射的组合。我们发现，平均恒星形成和超大质量黑洞吸积速率密度的演化类似于（1+z）^[3]，这与在明亮的、可单独探测的星暴星系和活动星系核样本中发现的趋势一致。我们的工作也证实了许多以前的叠加分析微弱的源人口的结果，改进的统计。
