ALMA-ALPINE [CII] survey: The sub-kpc morphology of three main sequence galaxy systems at z ∼ 4.5 revealed by ALMA

Abstract

Going from a redshift of 6 down to nearly 4, galaxies grow rapidly from low-mass galaxies towards the more mature types of massive galaxies seen at cosmic noon. Growth via gas accretion and mergers undoubtedly shape this evolution, however, there is considerable uncertainty at present over the contribution of each of these processes to the overall evolution of galaxies. Furthermore, previous characterisations of the morphology of galaxies in the molecular gas phase have been limited by the coarse resolution of earlier observations. In this work, we utilise new high-resolution ALMA CII observations to analyse three main sequence (MS) galaxy systems at a redshift of $z and at resolutions of up to $0.15''$. This approach enables us to investigate the morphology and kinematics on a kpc scale and understand the processes at play as well as the classifications of galaxies at high resolution. Thanks to this unique window, we are able to gain insights into the molecular gas of MS galaxies undergoing mass assembly in the early Universe We used intensity and velocity maps, position-velocity diagrams, and radial profiles of CII in combination with dust continuum maps to analyse the morphology and kinematics of the three systems. In general, we find that the high-resolution ALMA data reveal more complex morpho-kinematic properties. For one galaxy in our sample, we identified interaction-induced clumps, demonstrating the profound effect that mergers have on the molecular gas in galaxies, which is consistent with what has been suggested by recent simulations. One galaxy that was previously classified as dispersion-dominated turned out to show two bright CII emission regions, which could either be classified as merging galaxies or massive star-forming regions within the galaxy itself. The high-resolution data for the other dispersion dominated object also revealed clumps of CII that had not been identified previously. Within the sample, we might also detect star-formation powered outflows (or outflows from active galactic nuclei) that appear to be fuelling diffuse gas regions and enriching the circumgalactic medium. The new high-resolution ALMA data we present in this paper reveal that the galaxies in our sample are much more complex than they previously appeared in the low-resolution ALPINE data. In particular, we find evidence of merger induced clumps in the galaxy DC8187, along with signs of merging components for the other two objects. This may be evidence that the number of mergers at high redshift are significantly underestimated at present.

Dead or Alive? How Bursty Star Formation and Patchy Dust Can Cause Temporary Quiescence in High-redshift Galaxies

“…Several studies based on Atacama Large Millimeter/ submillimeter Array (ALMA) observations suggest a significant fraction of dust in galaxies even at z ∼ 7 (e.g., Faisst et al 2020a;Fudamoto et al 2020Fudamoto et al , 2021Inami et al 2022;Mitsuhashi et al 2023). Furthermore, thanks to large ALMA surveys such as ALPINE (Béthermin et al 2020;Faisst et al 2020b;Le Fèvre et al 2020) and REBELS (Bouwens et al 2022), we have statistical evidence of spatial displacement between UV and far-IR emission in high-z galaxies (e.g., Jones et al 2020;Fudamoto et al 2021;Béthermin et al 2023;Devereaux et al 2024). This suggests distinct regions of high and low dust obscuration.…”