三个邻近BL的Ly α发射
Broad Ly alpha Emission from Three Nearby BL Lacertae Objects
摘要：
我们目前的远紫外HST/COS光谱附近的BL Lac对象。BL Lac光谱主要由一个光滑的，幂律连续出现在一个相对论性喷流。然而，光谱并不一定是无特征的;在高质量的光谱中有时会看到微弱的宽线和/或窄线发射。我们在Mrk 421（z=0.030）和PKS 2005 -489（z=0.071）的HST/COS光谱中检测到Lya发射，以及Mrk 501（z=0.0337）的HST/GHRS观测。PKS 2155 -304（z=0.116）的存档HST/STIS观测结果显示，在非常低的上限下没有Lya发射。使用的假设，宽线区域（BLR）云不对称地放置在AGN周围，我们使用这些测量的Lya发射功能，以约束相对论伽玛值的电离连续产生的射流（在电离有界的情况下）或质量的温暖的气体（在密度有界的情况下）。虽然可以获得所有四种情况下的实际伽马值，但Mrk 421和PKS 2155 -304的值足够高，表明可能需要约1-2%的宽线区域云的覆盖因子，以提供与这类BL Lac建议的多普勒增强和视角的早期值的一致性。这种差异也存在于M87的情况下，在我们的方向上的多普勒增强量预计是最小的，再次暗示了宽线区域云的覆盖因子很小。如果像这些小的覆盖因子所暗示的那样，密度约束模型的假设可能更正确，那么观测到的Lya光度就要求BL 1、Lac/FRI核中只有非常少的暖气体（10^-4 ~ 10^-5 Msun），正如Guilbert、Fabian和McCray（1983）所暗示的那样。如果这些云与较热的气体（~10^6 K）处于压力平衡状态，那么BLR包含的质量太少，无法单独通过吸积为活动星系核提供动力。
英文摘要：
We present far-UV HST/COS spectra of four nearby BL Lac Objects. BL Lac spectra are dominated by a smooth, power-law continuum which arises in a relativistic jet. However, the spectra are not necessarily featureless; weak, broad- and/or narrow-line emission is sometimes seen in high-quality optical spectra. We present detections of Lya emission in HST/COS spectra of Mrk421 (z=0.030) and PKS2005-489 (z=0.071) as well as an archival HST/GHRS observation of Mrk501 (z=0.0337). Archival HST/STIS observations of PKS2155-304 (z=0.116) show no Lya emission to a very low upper limit. Using the assumption that the broad-line region (BLR) clouds are asymmetrically placed around the AGN, we use these measured Lya emission features to constrain either the relativistic Gamma values for the ionizing continuum produced by the jet (in the ionization-bounded case) or the mass of warm gas (in the density-bounded case). While realistic Gamma values can be obtained for all four cases, the values for Mrk421 and PKS2155-304 are high enough to suggest that covering factors of broad-line-region clouds of ~1-2% might be required to provide consistency with earlier values of Doppler boosting and viewing angles suggested for this class of BL Lacs. This discrepancy also exists in the case of M87, where the amount of Doppler boosting in our direction is expected to be minimal, again suggestive of a small covering factor of broad-line-region clouds. If, as these small covering factors might suggest, the assumptions of a density-bounded model could be more correct, then the observed Lya luminosities require that BL\,Lac/FRI nuclei possess very little warm gas (10^-4 to 10^-5 Msun) as suggested by Guilbert, Fabian & McCray (1983). If these clouds are in pressure balance with a hotter (~10^6 K) gas, the BLR contains too little mass to power the AGN by accretion alone.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
