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

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 (czgal = 1204± 3 km s, LB ∼ 0.09 L, current star formation rate = 0.08–0.24 h 70 M⊙ yr ) and 33 h 70 kpc (6. 6) from its nucleus. We find that IC 691 has an H I mass of MH I = (3.6± 0.1)× 10 M⊙ and a dynamical mass of Mdyn = (3.1± 0.5) × 10 h 70 M⊙. The UV spectrum of SBS 1122+594 shows a metal-line (Lyα+C IV) absorber near the redshift of IC 691 at czabs = 1110 ± 30 km s. 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⊙] ∼ −0.7) and the metal-line absorber ([Z/Z⊙] < −0.3). We also find that the galaxy’s escape velocity at the absorber location is vesc = 80 ± 10 km s and derive a wind velocity of vw = 160± 50 km s. 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. Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309; [email protected], [email protected] NSF Astronomy and Astrophysics Postdoctoral Fellow, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; [email protected] Yale Center for Astronomy and Astrophysics, Departments of Physics and Astronomy, Yale University, New Haven, CT 06520; [email protected] Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637