Disentangling the multiphase circumgalactic medium shared between a dwarf and a massive star-forming galaxy at z∼0.4

Themultiphase circumgalactic medium (CGM) arises within the complex environment around a galaxy, or collection of galaxies, and possibly originates from a wide range of physical mechanisms. In this paper, we attempt to disentangle the origins of these multiphase structures and present a detailed analysis of the quasar field Q0122-003 field using Keck/KCWI galaxy observations and HST/COS spectra probing the CGM. Our re-analysis of this field shows that there are two galaxies associated with the absorption. We have discovered a dwarf galaxy, G 27kpc (M = 108.7M⊙), at z = 0.39863 that is 27 kpc from the quasar sightline. G 27kpc is only +21 km s-1 from a more massive (M = 1010.5M⊙) star-forming galaxy, G 163kpc, at an impact parameter of 163 kpc. While G 163kpc is actively forming stars (SFR = 6.9M⊙ yr-1), G 27kpc has a low star-formation rate (SFR = 0.08 ± 0.03M⊙ yr-1) and star formation surface density (ΣSFR = 0.006M⊙ kpc-2 yr-1), implying no active outflows. By comparing galaxy SFRs, kinematics, masses, and distances from the quasar sightline to the absorption kinematics, column densities, and metallicities, we have inferred the following: (1) Part of the low-ionization phase has a metallicity and kinematics consistent with being accreted on to G 27kpc. (2) The remainder of the low ionization phase has metallicities and kinematics consistent with being intragroup gas being transferred fromG 27kpc toG 163kpc. (3) The high ionization phase is consistent with being produced solely by outflows originating from the massive halo of G 163kpc. Our results demonstrate the complex nature of the multiphase CGM, especially around galaxy groups, and that detailed case-by-case studies are critical for disentangling its origins.