Merger induced clump formation in distant infrared luminous starburst
  galaxies
  While the formation of stellar clumps in distant galaxies is usually
attributed to gravitational violent disk instabilities, we show here that major
mergers also represent a competitive mechanism to form bright clumps. Using
~0.1'' resolution ACS F814W images in the entire COSMOS field, we measure the
fraction of clumpy emission in 109 main sequence (MS) and 79 Herschel-detected
starbursts (off-MS) galaxies at 0.5 < z < 0.9, representative of normal versus
merger induced star-forming activity, respectively. We additionally identify
merger samples from visual inspection and from Gini-M20 morphological
parameters. Regardless of the merger criteria adopted, the clumpiness
distribution of merging systems is different from that of normal isolated disks
at > 99.5 % confidence level, with the former reaching higher clumpiness
values, up to 20 % of the total galaxy emission. We confirm the merger induced
clumpiness enhancement with novel hydrodynamical simulations of colliding
galaxies with gas fractions typical of z ~ 0.7. Multi-wavelength images of
three starbursts in the CANDELS field support the young nature of clumps, which
are likely merger products rather than older pre-existing structures. Finally,
for a subset of 19 starbursts with existing near-IR rest frame spectroscopy, we
find that the clumpiness is mildly anti-correlated with the merger phase,
decreasing towards final coalescence. Our result can explain recent ALMA
detections of clumps in hyperluminous high-z starbursts, while normal objects
are smooth. This work raises a question on the role of mergers on the origin of
clumps in high redshift galaxies in general.
