In the last decade, the far-infrared fine-structure [CII] line has become a workhorse for the study of early galaxies due to its brightness and accessibility from (sub)millimeter facilities at z>4. While several hundred galaxies at z>4 have been detected in [CII] emission so far, only a handful have [CII] resolved observations that enable studying the physical processes of galaxy assembly at these redshifts.

CRISTAL is a Cycle 8 ALMA large program that conducted sensitive [CII] high-resolution ALMA observations, which, combined with JWST imaging and spectroscopy, is producing the first systematic census on ∼kpc scales of the multi-phase gas, dust, and stars of typical star-forming galaxies at z∼4-6.

In the first part of this talk, we will show some of the first results from the CRISTAL survey, focusing on (1) A morpho-kinematic classification: combining the [CII] kinematics and the morphology from JWST/NIRCam images (mergers/satellites/disks?), (2) Existence of outflows and (3) Comparative analysis of sizes of the different ISM components ([CII], dust, rest-frame UV and stellar).

In the second part of this talk, we will focus on one particular system: CRISTAL-01, a complex interacting system composed by an obscured, massive submillimeter galaxy, a UV bright companion and a Lyman-alpha blob at z=4.5. We combine the ALMA CRISTAL [CII] imaging with data from previous programs targeting this system, and achieve a deep view into an unlensed DSFG and its rich environment at a 0.2” resolution. We identify an elongated [CII]-emitting structure with a projected size of 15 kpc stemming from the bright DSFG at the center of the field, with no clear counterpart at any other wavelength. The plume is oriented 40 deg away from the minor axis of the DSFG, and shows significant spatial variation of its spectral parameters. In particular, the [CII] emission shifts from 180 km/s to 400 km/s between the bottom and top of the plume, relative to the DSFG's systemic velocity. We discuss four possible scenarios to interpret the [CII] plume: a conical outflow, a cold accretion stream, ram pressure stripping, and gravitational interactions.

For Zoom connection information, please contact Emanuele Paolo Farina (emanuele.farina_at_noirlab.edu).

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