Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-05-18
Astronomy and Astrophysics
Astrophysics
Accepted for publication on Astronomy & Astrophysics, 15 pages, 8 figures
Scientific paper
10.1051/0004-6361:20065455
Aims: We present optical spectroscopy of a sample of BL Lac objects, to determine their redshift, to study their broad emission line properties and to characterize their close environment. Methods: Twelve objects were observed using the ESO 3.6m and the NOT 2.5m telescopes, obtaining spectra for the BL Lacs and for nearby sources. Results: For seven objects, nuclear emission lines and/or absorption lines from the host galaxy were detected. In all the four cases where absorption lines were revealed, the host galaxy has been resolved with HST or ground-based imaging. The broad H_alpha luminosities (or their upper limits) of the BL Lacs are similar to those of radio-loud quasars. For two BL Lacs, spectroscopy of close companions indicates that they are at the redshift of the BL Lacs, and therefore physically associated and likely interacting. Five BL Lacs have a featureless spectrum. In these cases, we apply a new technique to derive lower limits for their redshift. which are consistent with lower limits deduced from imaging.
Falomo Renato
Kotilainen Jari
Sbarufatti Boris
Treves Aldo
Парфенов Г. П.
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