The ALMA-CRISTAL Survey: Spatial extent of [CII] line emission in star-forming galaxies at z=4-6

ABSTRACT :
One of the major achievements in extragalactic studies with ALMA is the discovery of an extended feature of the [CII]158um line emission around star-forming galaxies during and after the Epoch of Reionization. We present the result of the ALMA-CRISTAL Survey, which provides a census of [CII] line and dust continuum emissions in a kpc scale for more than 20 individual galaxies at z=4-6. By modeling visibilities, we derive the effective radius of 34 components of [CII] line emission in total. These measurements comprise not only isolated galaxies but also interacting systems, thanks to the high spatial resolution of the data. We compare the [CII] sizes with the sizes of rest-frame ultra-violet (UV) and far-infrared (FIR) continua, which were measured from the HST F160W filter and ALMA Band-7 continuum images, respectively. We confirm that the [CII] line emission is spatially extended more than the continuum emissions, with average size ratios of 2.90 and 1.54, although about half of the FIR-detected sample show comparable spatial extent between [CII] line and FIR continuum emissions. Overall, our results suggest that the spatial extent of [CII] line emission can mostly be explained by star formation activity, while the contribution from diffuse neutral medium and the effects of mergers and outflows may further expand the [CII] line distributions. Finally, we also present the correlations between the properties of [CII] line, dust, and Lyα emissions.