BL Lacertae (BL Lac) objects are a type of active galactic nucleus (AGN) characterized by featureless optical spectra, where a relativistic jet is oriented toward the observer. By studying BL Lacs objects, we improve our understanding of accretion processes, high-energy particle acceleration, magnetic field structures in extreme environments, and galaxy formation and evolution. Generally, luminous AGNs (i.e., quasars) exhibit “positive” evolution. This means that, on average, quasars are more numerous and/or more luminous in the early Universe, at higher redshifts, than they are today. However, the evolution of BL Lacs has been long disputed, in part due to selection biases and small sample sizes. Here we perform the luminosity–volume test of BL Lac evolution on a uniformly selected sample and find that BL Lacs instead exhibit mild negative evolution. We conclude by putting our results into context with previous studies on BL Lac evolution.

中文翻译：

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斯隆数字巡天中 BL Lac 天体的负宇宙演化

BL Lacertae (BL Lac) 天体是一种活动星系核 (AGN)，其特征在于无特征的光谱，其中相对论射流朝向观察者。通过研究 BL Lacs 天体，我们提高了对吸积过程、高能粒子加速、极端环境中的磁场结构以及星系形成和演化的理解。一般来说，发光活动星系核（即类星体）表现出“正”演化。这意味着，平均而言，早期宇宙中类星体的数量和/或亮度更高，红移更高，比现在要多。然而，BL Lacs 的进化长期以来一直存在争议，部分原因是选择偏差和小样本量。在这里，我们对均匀选择的样本进行 BL Lac 演化的光度-体积测试，发现 BL Lacs 相反表现出轻微的负演化。最后，我们将我们的结果与之前关于 BL Lac 进化的研究结合起来。