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Far-Ultraviolet Observations of Outflows from IR-Luminous Galaxies

We obtained medium-resolution ultraviolet (UV) spectra between 1150 and 1450 Angstroms of the four UV-bright, infrared (IR)-luminous starburst galaxies IRAS F08339+6517, NGC 3256, NGC 6090, and NGC 7552 using the Cosmic Origins Spectrograph onboard the Hubble Space Telescope. The selected sightlines towards the starburst nuclei probe the properties of the recently formed massive stars and the physical conditions in the starburst-driven galactic superwinds. Despite being metal-rich and dusty, all four galaxies are strong Lyman-alpha emitters with equivalent widths ranging between 2 and 13 Angstroms. The UV spectra show strong P Cygni-type high-ionization features indicative of stellar winds and blueshifted low-ionization lines formed in the interstellar and circumgalactic medium. We detect outflowing gas with bulk velocities of about 400 km/s and maximum velocities of almost 900 km/s. These are among the highest values found in the local universe and comparable to outflow velocities found in luminous Lyman-break galaxies at intermediate and high redshift. The outflow velocities are unlikely to be high enough to cause escape of material from the galactic gravitational potential. However, the winds are significant for the evolution of the galaxies by transporting heavy elements from the starburst nuclei and enriching the galaxy halos. The derived mass outflow rates of ~100 Msol/yr are comparable to, or even higher than the star-formation rates. The outflows can quench star formation and ultimately regulate the starburst as has been suggested for high-redshift galaxies.