# Formation of disc galaxies around z~2

## TL;DR

This study investigates the morphological and stellar evolution of galaxies around redshift 2, revealing significant growth in disc components and insights into galaxy formation and quenching processes during this epoch.

## Contribution

It provides a detailed analysis of bulge-disc decomposition and the evolution of galaxy morphology and stellar properties across z~2, highlighting the increasing prevalence of two-component systems.

## Key findings

- Increase in two-component systems from 46% to 70% across z=2
- Doubling of stellar mass and halving of SFR in two-component systems
- Pure discs grow in size and mass, while spheroids remain stable

## Abstract

We present combined evolution of morphological and stellar properties of galaxies on the two sides of z=2 (2.0<z<4.0 and 1.5<z<2.0) in CDFS, with ground-based spectroscopic redshifts. We perform bulge-disc decomposition on their images in J and H filters, from the 3DHST Legacy Survey obtained using HST/WFC3. Combining morphological information with stellar properties, we provide a detailed account of the formation/growth of discs and spheroids around z~2. The fraction of 2-component (bulge+disc) systems increases from ~46% for z>2 to ~70% for z<2, compensating for the fall in population of pure discs and pure spheroids. All quiescent outliers of our full sample on the main-sequence, are 2-component systems, belonging to the lower redshift range (z<2). The doubling of stellar mass of 2-component systems and decrease in their SFR by the same factor, suggests that mechanisms involved in morphological transformations are also responsible for the quenching of their star formation activity. Interestingly, while there is substantial increase in the size (~2.5 times) and mass (~5 times) of pure discs, from z>2 to z<2, pure spheroids maintain roughly the same values. Additionally, while bulge hosting discs witness an expansion in scale length (~1.3 times), their bulge sizes as well as bulge to total light ratio see no evolution, suggesting that z~2 is pre-dominantly a disc formation period.