Galaxy Formation and Evolution

One of the most interesting findings of recent ALMA [CII]158um galaxy surveys (e.g. ALPINE, REBELS, CRISTAL) has been the clear presence of extended [CII] line emission among massive star-forming galaxies at z=4-6, beyond the rest-frame UV and dust continuum emission and extending out to ~10-kpc. Despite being key to understanding the interplay between star formation activity and feedback processes in the circumgalactic medium (CGM), the origin of such [CII] “halos’’ remains enigmatic. We have started a comprehensive program, titled “Origin of the [CII] Halos in Distant Systems” (ORCHIDS), aiming to unravel the nature of these extended [CII] features. Leveraging the capabilities of JWST/NIRSpec and Keck/KCRM IFU observations, through our awarded JWST GO3 program (ID: 5974; PI: M. Aravena, co-PI: J. González-López), we will scrutinize a carefully selected sample of eight massive star-forming galaxies at redshifts z~5-6. Our targets have been recently confirmed to exhibit [CII] halos through high-resolution ALMA imaging from the CRISTAL survey. Our observations are designed to rigorously test the most plausible scenarios predicting the nature of [CII] halos. These observations will yield a full characterization of the baryonic cycle in these systems, yielding a unique probe of (i) the kinematics and distribution of the star formation and ionized gas, enabling us to discern outflows, multiple component systems and extended dense atomic and ionized gas in the CGM as the origin for [CII] halos (JWST/NIRSpec + Keck/KCRM); (ii) test associations with Lyman-alpha halos/blobs; (iii) the galaxies’ gas excitation and shocks (JWST/NIRSpec); and (iv) provide resolved measurements of various star-forming tracers.