TRICEPS. I. Tracing cold gas, dust, and stars at sub-kpc scales in massive star-forming galaxies at z = 4-5

TRICEPS (Tracing Resolved Ionized Carbon Emission in Primeval Systems) is a new survey targeting 16 massive galaxies at z=4-5 with coordinated ALMA and JWST observations. The program combines ALMA band-7 [CII]-158 micron line data to map cold gas distribution and kinematics at about 0.1 arcsec (roughly 0.8 kpc) resolution, ALMA rest-frame 160 micron continuum maps to trace dust at similar resolution, multi-band JWST NIRCam and MIRI imaging to trace stellar mass and star formation at 0.1-0.2 arcsec resolution, and multi-line CO observations from ALMA and the VLA, including CO(1-0), to measure molecular gas content. This first paper describes the survey's scientific goals, sample properties, and ALMA band-7 observations.

The galaxies were selected solely on bright [CII] fluxes (>2 Jy km/s). They sit at the top end of the star-forming main sequence at z=4-5, with stellar masses of about 10^10.5-10^12 solar masses and star-formation rates of about 100-3000 solar masses per year. By survey design, half of the targets are in galaxy pairs; clear tidal interaction signs are present in three of the four pairs. To date TRICEPS is the largest sample at z=4-5 with exceptionally well resolved gas distribution and kinematics, yielding on average 46 resolution elements per galaxy at signal-to-noise ratio higher than 3.

In every galaxy, the [CII] velocity fields display regular rotation, although interacting galaxies tend to be somewhat more disturbed. The authors conclude that regular rotation appears ubiquitous among massive star-forming galaxies when the Universe was less than about 1.5 Gyr old.