COS-EDGES: Co-rotation and Kinematic Stratification of the Multi-Phase CGM Around Edge-On Galaxies

We present the first results from the COS-EDGES survey, targeting the kinematic connection between the interstellar medium and multi-phase circumgalactic medium (CGM) in nine isolated, near-edge-on galaxies at z ∼ 0.2, each probed along its major axis by a background quasar at impact parameters of D = 13 – 38 kpc. Using VLT/UVES and HST/COS quasar spectra, we analyse Mg i , Mg ii , H i , C ii , C iii , and OV i absorption relative to galaxy rotation curves from Keck/LRIS and Magellan/MagE spectra. We find that low ionisation absorption for 8/9 galaxies lies below the halo escape velocity, indicating bound inflow or recycling gas, while 6/9 galaxies have high ionisation gas reaching above the halo escape velocity, suggesting some unbound material. We find that at lower D / R vir (0.12 ≤ D / R vir ≤ 0.20), over 80% of absorption in all ions lies on the side of systemic velocity matching disk rotation, and the optical-depth–weighted median velocity ( v abs) is consistent with the peak rotation speed. At higher D / R vir (0.21 ≤ D / R vir ≤ 0.31), the kinematics diverge by ionisation state: For the low ionisation gas, the amount of co-rotating absorption remains above 80%, yet v abs drops to roughly 60% of the galaxy rotation speed. For the high ionisation gas (OV i ), only 60% of the absorption is consistent with co-rotation and v abs drops to 20% of the galaxy rotation speed. Furthermore, the velocity widths, corresponding to 50% of the total optical depth ( ∆v 50 ) for low ionisation gas is up to 1.8 times larger in the inner halo than at larger radii, while for C iii and OV i ∆v 50 remains unchanged with distance. The 90% optical-depth width ( ∆v 90 ) shows a modest decline with radius for low ionisation gas but remains constant C iii and OV i . At high D / R vir both ∆v 50 and ∆v 90 increase with ionisation potential. These results suggest a radially dependent CGM kinematic structure: the inner halo hosts cool, dynamically broad gas tightly coupled to disk rotation, whereas beyond ≳ 0.2 R vir , particularly traced by OV i and H i , the CGM shows weaker rotational alignment and lower relative velocity dispersion. Therefore, low-ionisation gas likely traces extended co-rotating gas, inflows and/or recycled accretion, while high-ionisation gas reflects a mixture of co-rotating, lagging, discrete collisionally ionised structures and volume-filling warm halo, indicating a complex kinematic stratification of the multi-phase CGM.