BL Lacertae是“孤儿”AGN吗？对母体的多波段和光谱限制
Is BL Lacertae an "orphan" AGN? Multiband and spectroscopic constraints on the parent population
摘要：
我们分析了其原型BL Lacertae的光谱，以验证其宽Ha线的存在和可能的通量变化。我们还使用光谱信息来研究其亲本种群的问题。在2007-2008年，当源处于相对微弱的状态时，在TNG获得了四个光谱。在三种情况下，我们能够测量宽的Ha和几条窄的发射线。与以前的结果相比，宽Ha在10年内增加了约50%，这种变化对于宽线活动星系核来说并不罕见。我们根据它与球核光度的关系，估计BL Lac的黑洞质量为4-6 × 10^8太阳质量。从光谱数据估计的维里质量反而小了20-30倍。我们认为，这种差异是由于BL Lac BLR是欠发光。最后，我们解决了BL Lac母体的问题，比较其各向同性量与其他活动星系核类。从窄发射线谱的角度来看，该源位于低激发射电星系附近。当也考虑到它的漫射射电功率时，由于BL Lac的射电光度较低（在给定线光度下），与FRI射电星系的关联受到严重质疑。BL Lac的窄线和射电光度与微型射电星系的样本相匹配，但没有显示出BLR。然而，如果存在的话，“未对准的BL Lac”对象应该已经进入该样本。我们也排除了因为类星体的光学外观而被排除的可能性。观测上的限制表明BL Lac处于一个短暂的过渡阶段，在活动星系核中没有留下可探测的演化“痕迹”。我们推测一种情况下，可以解释所观察到的属性。[删节]
英文摘要：
We have analysed optical spectra of BL Lacertae, the prototype of its class, to verify the presence and possible flux variations of its broad Ha line. We used the spectroscopic information also to investigate the question of its parent population. Four spectra were acquired at the TNG in 2007-2008, when the source was in a relatively faint state. In three cases we were able to measure the broad Ha and several narrow emission lines. A comparison with previous results suggests that the broad Ha has increased by ~50% in ten years, a change not unusual for Broad Lined AGN. We estimated a black hole mass for BL Lac of 4-6 10^8 solar masses from its relation with the bulge luminosity. The virial mass estimated from the spectroscopic data is instead 20-30 times smaller. We suggest that this discrepancy is due to the BL Lac BLR being underluminous. Finally, we addressed the problem of the BL Lac parent population, comparing its isotropic quantities with those of other AGN classes. From the point of view of the narrow emission line spectrum, the source locates close to low-excitation radio galaxies. When also considering its diffuse radio power, an association with FRI radio galaxies is severely questioned due to the lower radio luminosity (at give line luminosity) of BL Lac. The narrow line and radio luminosities of BL Lac instead match those of a sample of miniature radio galaxies, which however do not show a BLR. Yet, if existing, "misaligned BL Lac" objects should have entered that sample. We also rule out the possibility that they have been excluded because of a QSO optical appearance. The observational constraints suggest that BL Lac is caught in a short term transient stage, which does not leave a detectable evolutionary "trace" in the AGN population. We speculate on a scenario that can account for the observed properties. [ABRIDGED]
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