The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs
The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs
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DOI：
10.1051/0004-6361:20041786
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发表时间：
2004-08
影响因子：
6.5
通讯作者：
J. Wall;C. Jackson;P. Shaver;I. Hook;K. Kellermann
中科院分区：
文献类型：
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作者：
J. Wall;C. Jackson;P. Shaver;I. Hook;K. Kellermann
我们从空间密度的角度分析了类星体的Parkes四分之一-Jansky平谱样本，包括红移分布、射电光度函数和红移截止的证据。关于光度函数，我们注意到空间密度从现在到对应于红移∼1的时代的强烈演化。我们提请注意由于光谱形状的扩散而产生的选择效应，这可能误导了其他研究人员将不同红移壳中光度函数的外观相似之处作为光度演化的证据。为了研究红移超过3的演化，我们发展了一个基于Vmax检验的独立于模型的方法，使用每个物体来预测超过z=3的预期密度。由此，我们证明了在z>；3处空间密度的减小存在显著水平>；4σ。我们发现在这种测定中存在严重的偏差，因为使用的通量密度测量的时间要比调查结果晚得多。估计了衰减的形式，并显示出与在X射线和光学波段中选择的类星体非常相似的形式。这一减少也与目前对恒星形成演化的估计进行了比较，结果不那么确凿。综上所述，我们认为再电离时代几乎不受强大的平谱类星体的影响，尘埃遮蔽在我们对射电、光学或X射线波长选择的类星体数量的看法中并不起主要作用。©ESO 2005年。
We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths. © ESO 2005.