Abstract
We study the nature of the low-redshift CGM in the Simba cosmological
simulations as traced by ultraviolet absorption lines around galaxies in bins
of stellar mass ($M_\star>10^10M_ødot$) for star-forming, green valley and
quenched galaxies at impact parameters $r_\perp1.25r_200$. We generate
synthetic spectra for HI, MgII, CII, SiIII, CIV, and OVI, fit Voigt profiles to
obtain line properties, and estimate the density, temperature, and metallicity
of the absorbing gas. We find that CGM absorbers are most abundant around star
forming galaxies with $M_< 10^11M_ødot$, while the abundance of green
valley galaxies show similar behaviour to those of quenched galaxies,
suggesting that the CGM "quenches" before star formation ceases. HI absorbing
gas exists across a broad range of cosmic phases (condensed gas, diffuse gas,
hot halo gas and Warm-Hot Intergalactic Medium), while essentially all
low-ionisation metal absorption arises from condensed gas. OVI absorbers are
split between hot halo gas and the WHIM. The fraction of collisionally ionised
CGM absorbers is $25-55\%$ for CIV and $80-95\%$ for OVI, depending
on stellar mass and impact parameter. In general, the highest column density
absorption features for each ion arise from dense gas. Satellite gas, defined
as that within $10r_1/2,\star,$ contributes $3\%$ of overall HI
absorption but $30\%$ of MgII absorption, with the fraction from
satellites decreasing with increasing ion excitation energy.
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