# Extended star-forming region within galaxies in a dense proto-cluster core at z=2.53

## TL;DR

This study uses high-resolution AO imaging to map star-forming regions within galaxies in a dense proto-cluster at z=2.53, revealing inside-out growth patterns similar to field galaxies, indicating secular processes dominate structural evolution.

## Contribution

It provides the first spatially resolved comparison of star-forming and stellar components in proto-cluster galaxies at z=2.5, highlighting environment-independent secular growth mechanisms.

## Key findings

- Star-forming regions are more extended than stellar components in proto-cluster galaxies.
- Inside-out growth of star-forming regions is observed at z=2.5.
- Structural evolution is driven mainly by internal processes, regardless of environment.

## Abstract

At $z\sim2$, star-formation activity is thought to be high even in high-density environments such as galaxy clusters and proto-clusters. One of the critical but outstanding issues is if structural growth of star-forming galaxies can differ depending on their surrounding environments. In order to investigate how galaxies grow their structures and what physical processes are involved in the evolution of galaxies, one requires spatially resolved images of not only stellar components but also star-forming regions within galaxies. We conducted the Adaptive Optics(AO)-assisted imaging observations for star-forming galaxies in a dense proto-cluster core at $z=2.53$ with IRCS and AO188 mounted on the Subaru Telescope. A combination of AO and narrow-band filters allows us to obtain resolved maps of H$\alpha$-emitting regions with an angular resolution of 0.1--0.2~arcsec, which corresponds to $\sim1$ kpc at $z\sim2.5$. Based on stacking analyses, we compare radial profiles of star-forming regions and stellar components and find that the star-forming region of a sub-sample with $\rm log(M_*/M_\odot)\sim10-11$ is more extended than the stellar component, indicating the inside-out growth of the structure. This trend is similar to the one for star-forming galaxies in general fields at $z=2-2.5$ obtained with the same observational technique. Our results suggest that the structural evolution of star-forming galaxies at $z=2-2.5$ is mainly driven by internal secular processes irrespective of surrounding environments.