The Impact of Starbursts on the CGM

I have read by Heckman et al.

They discuss about the impact of starbursts on the circumgalactic medium. Their method is to compare the properties of the absorption lines(Lya, CIV, SiII, OIV… ) around starbursts galaxies within about the viral radius of galaxies with ones around normal star-forming galaxies. The sample of starburst galaxies they used is from Comic Origins Spectrograph on the Hubble Space Telescope. The result is

1. The equivalent width of absorption lines around starburst galaxies are systematically higher than star-forming galaxies. (We can’t make strong statement for OIV and close regions to galactic center since their sample is few for them.) For Lya (saturated), the equivalent width traces the spread in velocity of the absorbing gas along the line of sight, while for the other(unsaturated and optical depth ~ 1), does the ionic column densities.

2. The FWHM and velocity offsets of Lya around starburst galaxies are wider than star-forming. These imply that the cloud traced by Lya is super-viral.

3. The ratios of equivalent width of Si III and CIV (unsaturated) lines to Lya (saturated) are larger too.

4.The amount of metals is enhanced around starburst galaxies and the dynamical state of the outer CGM is significantly different.

They discuss some models to explain these results. The main point is whether the unusual CGM cause starbursts or starbursts cause unusual CGM. They conclude the latter is reliable and explain how starburst driven galactic winds affect the CGM assuming the simple model. To understand the mechanism, I need to learn the galactic winds more.


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