The Hamburg/SAO Survey for low metallicity blue compact H II galaxies (HSS–LM) - I. The first list of 46 strong-lined galaxies

We present the description and the first resultsof a new project devoted to the search for extremely metal- deficient blue compact/H -galaxies (BCGs) and to the creation of a well selected large BCG sample with strong emission lines. Such galaxies should be suitable for reliable determination of their oxygen abundance through the measurement of the faint (O ) λ4363 A line. The goals of the project are two-fold: a) to discover a significant number of new extremely metal- poor galaxies (Z 1/20 Z� ), and b) to study the metallicity distribution of local BCGs. Selection of candidates for follow-up slit spectroscopy is performed on the database of objective prism spectra of the Hamburg Quasar Survey. The sky region is limited by δ ≥ 0 ◦ and b II ≤− 30 ◦ . In this paper we present the results of the follow-up spectroscopy conducted with the Russian 6m telescope. The list of observed candidates contained 52 objects, of which 46 were confirmed as strong-lined BCGs (EW((O ) λ5007) ≥ 100 A). The remaining five lower excitation ELGs include three BCGs, and two galaxies classified as SBN (Starburst Nucleus) and DANS (Dwarf Amorphous Nucleus Starburst). One object is identified as a quasar with a strong Lyα emission line near λ5000 A (z ∼ 3). We provide a list with coordinates, measured radial velocities, B-magnitudes, equiv- alent widths EW((O ) λ5007) and EW(Hβ) and for the 46 strong-lined BCGs the derived oxygen abundances 12+log(O/H). The abundances range between 7.42 and 8.4 (corresponding to metallicities between 1/30 and 1/3 Z� ). The sample contains four galaxies with Z 1/20 Z� , of which three are new discoveries. This demonstrates the high efficiency of the new project to find extremely metal-deficient galaxies. The radial velocities of the strong-lined ELGs range between 500 and 19000 kms −1 with a median value of ∼6400 kms −1 . The typical B-magnitudes of the galaxies presented are 17. m 0−18. m 0.