非常光度的BL Lac天体的光谱学
Spectroscopy of BL Lac objects of extraordinary luminosity
摘要：
目标。我们的目标是确定红移（或严格的下限）的一些明亮的BL Lacs对象。方法.我们使用ESO-VLT的摄谱仪X-Shooter获得了4个红移未知的明亮BL Lac天体的中等分辨率光学和近红外光谱。结果尽管光谱的质量很高，观测的光谱范围很广，但我们还没有发现这些源的光谱特征。然而，我们能够提供严格的下限，他们的红移。特别地，对于两个TeV源PG 1553+113和H 1722+119，我们分别推断z > 0.30和z > 0.35。我们还检测到一个干预钙II吸收双峰的光谱MH 2136-428，这是归因于附近的巨大椭圆星系在\sim 100千秒差距的投影距离的晕。结论.在所有BL Lac都由明亮的核球主导的星系主持的假设下，目前对明亮BL Lac的光谱观测表明，这些物体可能是具有极强束核发射的来源。我们目前的模拟显示在何种情况下，它将有可能探测这一假设从检测非常弱的反射使用下一代的超大型光学望远镜。
英文摘要：
Aims. We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. Methods. We secured medium resolution optical and near-infrared spectra of 4 bright BL Lac objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. Results. In spite of the high quality of the spectra and the extended spectral range of the observations we have not detected intrisic spectral features for these sources. However we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119 we infer z > 0.30 and z > 0.35 respectively. We also detect an intervening Ca II absorption doublet in the spectrum of MH 2136-428 that is ascribed to the the halo of a nearby giant elliptical galaxy at \sim 100 kpc of projected distance. Conclusions. Under the hypothesis that all BL Lacs are hosted by luminous bulge dominated galaxies, the present state of art spectroscopic observations of bright BL Lacs indicate that these objects are likely sources with extremely beamed nuclear emission . We present simulations to show under which circustances it will be possible to probe this hypothesis from the detection of very weak absorptions using the next generation of extremely large optical telescopes.
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