Discovery of a Metal-Line Absorber Associated with a Local Dwarf Starburst Galaxy

Abstract

We present optical and near-infrared images, H I 21 cm emission maps, optical spectroscopy, and Hubble Space Telescope Space Telescope Imaging Spectrograph ultraviolet spectroscopy of the QSO/galaxy pair SBS 1122+594/IC 691. The QSO sight line lies at a position angle of 27° from the minor axis of the nearby dwarf starburst galaxy IC 691 (cz_gal=1204+/-3 km s^-1, L_B~0.09L^*, current star formation rate=0.08-0.24 h^-2₇₀ M_solar yr^-1) and 33 h^-1₇₀ kpc (6.6 arcmin) from its nucleus. We find that IC 691 has an H I mass of M_HI=(3.6+/-0.1)×10⁸ M_solar and a dynamical mass of M_dyn=(3.1+/-0.5)×10¹⁰ h^-1₇₀ M_solar. The UV spectrum of SBS 1122+594 shows a metal-line (Lyα+C IV) absorber near the redshift of IC 691 at cz_abs=1110+/-30 km s^-1. Since IC 691 is a dwarf starburst and the SBS 1122+594 sight line lies in the expected location for an outflowing wind, we propose that the best model for producing this metal-line absorber is a starburst wind from IC 691. We place consistent metallicity limits on IC 691 ([Z/Z_solar]~-0.7) and the metal-line absorber ([Z/Z_solar]<-0.3). We also find that the galaxy's escape velocity at the absorber location is v_esc=80+/-10 km s^-1 and derive a wind velocity of v_w=160+/-50 km s^-1. Thus, the evidence suggests that IC 691 produces an unbound starburst wind that escapes from its gravitational potential to transport metals and energy to the surrounding intergalactic medium.