Optical spectroscopy of BL Lacertae objects. Broad lines, companion galaxies and redshift lower limits

Abstract

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.

Accepted for publication on Astronomy & Astrophysics, 15 pages, 8 figures

References in corpus (2)

• ESO-VLT optical spectroscopy of BL Lac objects: II. New redshifts, featureless objects and classification assessments
• Ongoing Star Formation in the BL Lacertae object PKS 2005-489

Cited by in corpus (16)

• Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects
• Discovery of Very High Energy gamma-rays from 1ES 1011+496 at z=0.212
• The Central Engines of Fermi Blazars
• On the redshift of TeV BL Lac objects
• The redshift-dependence of gamma-ray absorption in the environments of strong-line AGN
• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
• On the BL Lacertae objects/radio quasars and the FRI/II dichotomy
• Optical spectroscopic survey of a sample of Unidentified Fermi objects
• Optical spectroscopy of BL Lac objects: TeV candidates
• Optical spectroscopy of Blazars for the Cherenkov Telescope Array
• Discovery of Very High Energy Gamma Rays from 1ES 1440+122
• ZBLLAC -- A spectroscopic database of BL Lacertae objects
• Powerful Radio Sources in the Southern Sky. I. Optical Identifications
• Powerful Radio Sources in the Southern Sky. II. A SWIFT X-Ray Perspective
• Probing cluster environments of blazars through gamma-gamma absorption
• Properties and Possible Physical Origins of $\gamma$-ray Emission in Extreme Synchrotron Blazars