2004/03/12 by Xinwu Cao · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/420893
published as Astrophys.J. 609 (2004) 80-84 · 5 pages, accepted for publication in ApJ
arxiv created 2004/03/12 · openalex publication_date 2004/06/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
The masses of central massive black holes in BL Lac objects are estimated from their host galaxy absolute magnitude R at R -band by using the empirical relation between R and black hole mass M bh . Only a small fraction of BL Lac objects exhibit weak broad-line emission, and we derive the sizes of the broad-line regions (BLRs) in these BL Lac objects from the widths of their broad emission lines on the assumption of the clouds being virilized in BLRs. It is found that the sizes of the BLRs in these sources are usually 2-3 orders of magnitude larger than those expected by the empirical correlation R BLR -λ L λ (3000 Å) defined by a sample of Seyfert galaxies and quasars. We discuss a variety of possibilities and suggest that this difference can probably be attributed to anisotropic motion of the BLR clouds in these BL Lac objects. If the BLR geometry of these sources is disklike, the viewing angles between the axis and the line of sight are in the range ~2°-12°, which is consistent with the unification schemes.