Deep spectroscopy of the low-metallicity blue compact dwarf galaxy SBS 0335-052^*

¹ Main Astronomical Observatory, Ukrainian National Academy of Sciences, Golosiiv, Kyiv 03680, Ukraine
² W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743, USA
³ Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, 14 Av. E. Belin, 31400 Toulouse, France

Corresponding author: Y. I. Izotov, izotov@mao.kiev.ua

Received: 1 August 2001
Accepted: 10 September 2001

Abstract

The results of deep long-slit spectroscopy of the extremely low-metallicity blue compact dwarf (BCD) galaxy SBS 0335-052 are presented. Down to intensity levels of 10 of H Hβ, unprecedented for spectroscopy of extra-galactic giant H ii regions, we detect numerous weak permitted and forbidden nebular lines in the brightest part of the galaxy. With varying degrees of confidence, the detections include lines of high-ionization ions like Fe⁴⁺-Fe⁶⁺, implying very hard ionizing radiation. Two broad emission features, possibly from Wolf-Rayet stars, and stellar He ii λ4200 absorption are seen in the same region. The large spatial extent of He ii λ4686 emission (implying the presence of sufficient ionizing photons with energies above 54 eV) and the spatial distribution of the electron temperature suggest that at least some part of the hard radiation is associated with shocks. Extended Hα emission is detected over ~6-8 kpc, a much larger area than in previous studies, suggesting that hot ionized gas is spread out far away from the central ionizing clusters. This shows that nebular line and continuous emission can significantly modify the colours of these extended regions and must be taken into account in studies of the underlying stellar population.