The Physical Nature of Circumgalactic Medium Absorbers in Simba

Sarah Appleby, Romeel Davé, Daniele Sorini, Weiguang Cui, Jacob Christiansen

Submitted on 8 July 2022


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>1010M) for star-forming, green valley and quenched galaxies at impact parameters r1.25r200. 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<1011M, 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 2555% for CIV and 8095% 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 10r1/2,, contributes 3% of overall HI absorption but 30% of MgII absorption, with the fraction from satellites decreasing with increasing ion excitation energy.


Comment: 19 pages, 12 figures; comments welcome

Subject: Astrophysics - Astrophysics of Galaxies