Optical spectroscopy of BL Lac objects: New redshifts and mis-identified sources

¹ Università di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
² Università dell' Insubria, via Valleggio 11, 22100 Como, Italy e-mail: treves@uninsubria.it
³ Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: falomo@pd.astro.it
⁴ Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland e-mail: jarkot@astro.utu.fi
⁵ European Southern Observatory, ESO Headquarter Garching, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany e-mail: mhulrich@eso.org

Corresponding author: N. Carangelo, nicoletta.carangelo@mib.infn.it

Received: 23 January 2003
Accepted: 12 June 2003

Abstract

We are carrying out a multi-purpose program of high signal to noise optical spectroscopy at medium resolution of 30 BL Lac objects. Here we report the detection of three new redshifts, and the discovery of three misclassified sources. The new redshifts refer to PKS 0754+100 (), H-1914-194 () and 1ES0715-259, for which we derive a redshift of  and also a “new” classification a Steep Spectrum Radio Quasar. In two cases (UM493 and 1620+103) stellar spectra indicate a wrong classification. The three sources with new redshift measurement show strong [OIII] emission in their spectra and their host galaxy properties are known. The central black hole masses derived using the and the M_BH-σ([OIII]) relations are compared.