# The structural properties of classical bulges and discs from z~2

## TL;DR

This study examines the evolution of bulges and discs in massive galaxies from z~2 to z~0, revealing similar structural properties across different galaxy types and challenging existing bulge formation models.

## Contribution

It provides a comprehensive analysis of the mass-size relation of bulges and discs over cosmic time using 2-component Sersic models, highlighting their similar properties regardless of galaxy morphology or star formation activity.

## Key findings

- Discs and star-forming galaxies follow similar mass-size relations.
- Bulges have a less steep mass-size relation than quiescent galaxies.
- Structural properties show little dependence on galaxy morphology or star formation activity.

## Abstract

We study the rest-frame optical mass-size relation of bulges and discs from z~2 to z~0 for a complete sample of massive galaxies in the CANDELS fields using 2 component S\'ersic models (Dimauro et a. 2018). Discs and star forming galaxies follow similar mass-size relations. The mass-size relation of bulges is less steep than the one of quiescent galaxies (best fit slope of ~ 0.7 for quiescent galaxies against ~ 0.4 for bulges). We find little dependence of the structural properties of massive bulges and discs with the global morphology of galaxies (disc vs. bulge dominated) and the star formation activity (star-forming vs. quiescent). This result suggests similar bulge formation mechanisms for most massive galaxies and also that the formation of the bulge component does not significantly affect the disc structure. Our findings pose a challenge to models envisioning multiple channels for massive bulge growth, such as disc instabilities and mergers.