HS 0822+3542 - a new nearby extremely metal-poor galaxy

Kniazev A.Y.1 - Pustilnik S.A.1 - Masegosa J.2 - Márquez I.2 - Ugryumov A.V.1 - Martin J.-M.3 -
Izotov Y.I.4 - Engels D.5 - Brosch N.6 - Hopp U.7 - Merlino S.2 - Lipovetsky V.A.1

Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Circessia, 369167, Russia - Instituto de Astrofisica de Andalucia, CSIC, Aptdo. 3004, 18080 Granada, Spain - Observatoire de Paris-Meudon, 92195 Meudon, France - Main Astronomical Observatory, Goloseevo, Kiev-127, 03680, Ukraine - Hamburger Sternwarte, Gojenbergswerg 112, D-21029 Hamburg, Germany - Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel - Universitätssternwarte München, D-81679 München, Germany

Abstract:

We present the results of spectrophotometry and BVR CCD photometry, as well as integrated H I radio measurements of a new blue compact galaxy (BCG) HS 0822+3542 with extremely low oxygen abundance: 12 + log(O/H) = 7.35, or 1/36 of solar value. The galaxy is the third most metal-deficient BCG after I Zw 18 and SBS 0335-052. Its very high mass fraction of gas ( $\approx$ 95% of all visible mass) and blue colours of underlying nebulosity are also similar to those of SBS 0335-052. This suggests that HS 0822+3542 is one of the nearest and dimmest galaxies experiencing a recently-started first star formation (SF) episode. Its properties imply that for such galaxies there is a linear scaling of the main parameters, at least for the baryon mass range (0.3-20) $\times$ 10⁸ $M_{\odot}$ . The total mass estimate indicates that the galaxy is dynamically dominated by a dark matter (DM) halo, which itself is one of the least massive for galaxies.

galaxies: fundamental parameters - galaxies: starburst - galaxies: abundances - galaxies: photometry - galaxies: individual (HS 0822+3542)