The Hamburg/SAO Survey for low metallicity blue compact/HII galaxies (HSS-LM)

I. The first list of 46 strong-lined galaxies

Astronomy & Astrophysics 397, 463 (2003)

A.V. Ugryumov [1,4], D. Engels [2], S.A. Pustilnik [1,4], A.Y. Kniazev [1,3,4], A.G. Pramskij [1,4], H.-J. Hagen [2],

  1. Special Astrophysical Observatory RAS, Nizhnij Arkhyz, Karachai-Circassia,369167 Russia
  2. Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
  3. Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany
  4. Isaac Newton Institute of Chile, SAO Branch

Abstract

We present the description and the first results of a new project devoted to the search for extremely metal-deficient blue compact/HII-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 III] λ 4363 Å 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_sun, 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 6 m telescope. The list of observed candidates contained 52 objects, of which 46 were confirmed as strong-lined BCGs (EW([OIII] λ 5007) >100 Å). 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 λ 5000 Å (z=3). We provide a list with coordinates, measured radial velocities, B-magnitudes, equivalent widths EW([OIII]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_sun). The sample contains four galxis with Z <= 1/20 Z_sun, 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 km/s with a median value of 6400 km/s. The typical B-magnitudes of the galaxies presented are 17.0-18.0.

Key words: galaxies: dwarf - galaxies: abundances - galaxie: distance and redshifts - surveys

Contact: Dieter Engels.

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