  Giant stellar clumps are ubiquitous in high-redshift galaxies. They are
thought to play an important role in the build-up of galactic bulges and as
diagnostics of star formation feedback in galactic discs. Hubble Space
Telescope (HST) blank field imaging surveys have estimated that these clumps
have masses up to 10$^{9.5}$ M$_{\odot}$ and linear sizes larger than ~1 kpc.
Recently, gravitational lensing has also been used to get higher spatial
resolution. However, both recent lensed observations and models suggest that
the clumps properties may be overestimated by the limited resolution of
standard imaging techniques. A definitive proof of this observational bias is
nevertheless still missing. Here we investigate directly the effect of
resolution on clump properties by analysing multiple gravitationally-lensed
images of the same galaxy at different spatial resolutions, down to 30 pc. We
show that the typical mass and size of giant clumps, generally observed at
$\sim$1 kpc resolution in high-redshift galaxies, are systematically
overestimated. The high spatial resolution data, only enabled by strong
gravitational lensing using currently available facilities, support smaller
scales of clump formation by fragmentation of the galactic gas disk via
gravitational instabilities.

Astrophysics of Galaxies