Abstract

We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved Hubble Space Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z similar to 1-3. We created continuum and emission line maps and pinpointed residual `blobs' detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes similar to 2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre 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, similar to 20 per cent and less than or similar to 80 per cent of the galaxy stellar mass, similar to 30 per cent and similar to 20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M-* greater than or similar to 10(9) M-circle dot) have lifetimes of similar to 650 Myr, and the less massive ones (10(8) < M-* < 10(9) M-circle dot) of similar to 145 Myr. This supports simulations predicting long-lived clumps (lifetime greater than or similar to 100 Myr). Finally, less than or similar to 30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation less than or similar to 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.