Mapping Large‐Scale Gaseous Outflows in Ultraluminous Galaxies with Keck II ESI Spectra: Variations in Outflow Velocity with Galactic Mass

Measurements of interstellar absorption lines in 18 ultraluminous infrared galaxies (ULIGs) have been combined with published data, in order to reassess the dependence of galactic outflow speeds on starburst luminosity and galactic mass. The Doppler shifts reveal outflows of relatively cool gas at $330 \\pm 100$km/s. The outflow speeds increase with the star formation rate (SFR) as roughly $v \\propto SFR^{0.35}$. This result is surprising since, in the traditional model for starburst-driven winds, these relatively cool gas clouds are accelerated by the ram pressure of a hot, supernova-heated wind that exhibits weak (if any) \\x temperature variation with increasing galactic mass. The lack of evidence for much…