# A contribution of star-forming clumps and accreting satellites to the mass assembly of z ~ 2 galaxies

## TL;DR

This study uses Hubble observations to analyze star-forming clumps and satellites in z ~ 2 galaxies, revealing their roles in galaxy mass assembly, their properties, and lifetimes, with implications for galaxy evolution models.

## Contribution

It distinguishes between in-situ formed clumps and accreting satellites, providing new insights into their properties, lifetimes, and contributions to galaxy mass assembly at z ~ 2.

## Key findings

- Extended blobs are larger and farther from galaxy centers.
- Compact blobs are less massive and younger, likely formed in-situ.
- Massive clumps have lifetimes around 650 Myr.

## Abstract

We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analyzed spatially-resolved Hubble Space Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ~ 1 - 3. We created continuum and emission line maps and pinpointed residual "blobs" detected after subtracting the galaxy disk. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ~ 2 kpc and comparable stellar mass and age as the galaxy disks, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the disks. Furthermore the extended blobs are typically found at larger distances from the galaxy barycenter than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in-situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose respectively ~ 20% and ~< 80% of the galaxy stellar mass, ~ 30% and ~ 20% of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (Mstar >~ 10^9 Msun) have lifetimes of ~ 650 Myr, and the less massive ones (10^8 < Mstar < 10^9 Msun) of ~ 145 Myr. This supports simulations predicting long-lived clumps (lifetime > 100 Myr). Finally, ~< 30% (13%) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ~< 10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.