The Impact of Starbursts on the Circumgalactic Medium

We present a study exploring the impact of a starburst on the properties of the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's stellar body and extending out to the virial radius (200 kpc). We obtained ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS) probing the CGM of 20 low-redshift foreground galaxies using background QSOs. Our sample consists of starburst and control galaxies. The latter comprises normal star-forming and passive galaxies with similar stellar masses and impact parameters as the starbursts. We used optical spectra from the Sloan Digital Sky Survey(SDSS) to estimate the properties of the starbursts, inferring average ages of 200 Myrs and burst fractions involving ~10% of their stellar mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the starburst and in 17%(2/12) of the control sample. The two control galaxies with CIV absorbers differed from the four starbursts in showing multiple low-ionization transitions and strong saturated Lyman-alpha lines. They therefore appear to be physically different systems. We show that the CIV absorbers in the starburst CGM represent a significant baryon repository. The high detection rate of this highly ionized material in the starbursts suggests that starburst-driven winds can affect the CGM out to radii as large as 200 kpc. This is plausible given the inferred properties of the starbursts and the known properties of starburst-driven winds. This would represent the first direct observational evidence of local starbursts impacting the bulk of their gaseous halos, and as such provides new evidence of the importance of this kind of feedback in the evolution of galaxies.