CLASSY III. The Properties of Starburst-driven Warm Ionized Outflows*

We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with Cosmic Origins Spectrograph (COS) data. The outflows are traced by blueshifted absorption lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static interstellar medium (ISM) from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow's mean velocity and velocity width, and find that both correlate in a highly significant way with the star formation rate, galaxy mass, and circular velocity over ranges of four orders of magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried out in the warm phase we observe. The outflows' mass-loading factor increases steeply and inversely with both circular and outflow velocity (log-log slope similar to-1.6), and reaches similar to 10 for dwarf galaxies. We find that the outflows typically carry about 10%-100% of the momentum injected by massive stars and about 1%-20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.

Automated summary

This article reports the analysis results of galactic outflows in 45 low-redshift starburst galaxies. The outflows are traced by blueshifted absorption lines of metals, and different line multiplets and doublets are used to determine various properties of the outflows. The study finds significant correlations between the outflows' mean velocity and velocity width with the star formation rate, galaxy mass, and circular velocity. The outflow rates of metals, mass, momentum, and kinetic energy are also estimated.