HS 0822+3542 - a new nearby extremely metal-poor galaxy
A. Y. Kniazev, S. A. Pustilnik, J. Masegosa, I. Marquez, A. V. Ugryumov, J. -M. Martin, Y. I. Izotov, D. Engels, N. Brosch, U. Hopp, S. Merlino, V. A. Lipovetsky
Abstract
We present the results of spectrophotometry and BVR CCD photometry, as well as integrated HI 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 (~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)x108 Msun. 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.
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