We are reaching a critical moment where sub-arcsec observations are key to disentangle the physical mechanisms that shaped young galaxies at z > 5. In this thesis, we explored the morphology and kinematics of the cold gas, star-forming, and stellar components of two massive star-forming galaxies at z = 5 – 7, using high-resolution (0.3′′) ALMA observations of the [CII] 158μm line emission. Our analysis shows that COS2987, at z = 6.8, is found to be composed of a main central source, a fainter north extension, and candidate [C II] companions located 10 kpc away. The agreement between the UV and [CII] surface brightness radial profiles rules out diffuse, extended [CII] emission in the main galaxy component. The [CII] velocity map reveals a velocity gradient in the north-south direction, as commonly found in rotating disk galaxies. Kinematical modeling returns a dispersion lower than the expected value from observation trends and semi-analytic models of high redshift galaxies.
The second galaxy CRISTAL-05 , at z = 5.54, is a complex close encounter surrounded by a disturbed carbon-rich gas. This is imprinted in the disturbed [C II] morphology and the separation of the two components in the position-velocity diagram. The central region is composed of two components, named C05-NW and C05-SE , with the former being the dominant one. A significant fraction of the [C II] arises beyond the galactic disk up to 10 kpc, while the regions forming new massive stars and the stellar component, as traced by rest-frame UV and optical imaging obtained with the Hubble Space Telescope and the James Webb Space Telescope, seems compact (r[CII] ∼ 4× rUV ). We argue that the extended [CII] emission is due to this close merger, which would have been impossible to discern with lower-resolution observations. Our analysis suggests that the galaxy assembly in the early universe is dominated by frequent episodes of satellite accretion, while mature rotating disk galaxies may already be in place. This work reinforces the importance of high-redshift resolution surveys in the high-resolution exploration of the properties and stages of the earliest galaxies in the universe.
(Text above corresponds to PhD thesis abstract)
Type of project: PhD thesis
Status: Finished. Graduated 2024
Researchers: ANA CAROLINA POSSES NASCIMENTO, Manuel Aravena, Jorge González-López
Funding source: Becas ANID, Basal CATA2