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

The multiphase 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_⋆ = 10^8.7 M_⊙), 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_⋆ = 10^10.5 M_⊙) star-forming galaxy, G_163kpc, at an impact parameter of 163 kpc. While G_163kpc is actively forming stars (SFR = 6.9 M_⊙ yr^-1), G_27kpc has a low star-formation rate (SFR = 0.08 ± 0.03 M_⊙ yr^-1) and star formation surface density (Σ_SFR = 0.006 M_⊙ 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 from G_27kpc to G_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.