Disturbed cold gas in galaxy and structure formation

Cold and cool gas (T ≤ 10 ⁴ K) in the circumgalactic medium (CGM) and its interaction with galaxies remain poorly understood. Simulations predict that cold gas flows into galaxies through cosmic filaments, determining the disk formation and galaxy evolution. The cold gas accretion modes in the CGM and their dependence on dark matter halo mass and redshift remain puzzling. Resolving the kiloparsec-scale kinematics and dynamics of cold gas interacting with the disk, dust, and metals in different environments is particularly lacking at z > 2. Here we report two disturbed cold gas structures traced by ultra-strong MgII absorbers (rest-frame equivalent width Wr > 2 Å) exhibiting high kinematic velocities (> 500 km/s) and their environments at z ~ 4.9 and z ~ 2.6. Observations were conducted with VLT/MUSE, JWST/NIRCam, and ALMA to detect Lyα and nebular emission lines, as well as dust continuum emission in the vicinity of these two absorbing gas structures. We identify two Lyα emitters associated with a strong MgII absorber pair separated by ~1000 km/s at z ~ 4.87. The pair exhibits relative differences in metallicity, dust content, and ionization states, suggesting internal metal and dust exchange within the ultra-large cold gas structure. For the strong MgII absorber at z = 2.5652, we detect a dusty star-forming galaxy at a projected distance of D = 38 kpc. This galaxy exhibits prominent HeI, [SIII], and Paschenγ lines, along with significant dust continuum. It has a star formation rate of ~ 121+/-33 M☉/yr and likely harbors a rotating disk. These findings tentatively suggest that cold gas at high redshifts plays a critical role in driving disk formation and actively participates in the transfer of metals and dust within the overdense regions of the CGM.