Title: The birth of a giant star forming clump in a disk galaxy at redshift z = 2

Abstract:
Giant star forming clumps are typical morphological features of z ~ 2 galaxies, likely formed by 
violent gravitational instabilities in highly turbolent, gas-rich galaxy disks. However, their 
formation phase has never been observed. Furthermore, their fate is still highly debated: it is not 
understood yet if they migrate inward and coalesce to form the galaxy bulge or if they are 
disrupted by stellar feedback. 
With a data set of ultra deep HST/WFC3 imaging and slitless spectroscopy, we selected a 
sample of 68 [OIII] emitters at z ~ 2. From spatially resolved [OIII], Hb and [OII] emission line 
maps we serendipitously discovered a bright, off-nuclear, unresolved emission arising in the disk 
of a galaxy at z = 2. Despite its high contribution to the total star formation rate (SFR) of the 
galaxy (~ 40%), this feature is not detected in the continuum. We are thus observing, for the 
first time, a newly formed clump, in the very early phase of its collapse (age < 10 Myr). With a 
specific SFR 30 times higher than the one of the whole galaxy, this clump is behaving like a 
galactic miniature of starburst, showing that violent disk instability can induce high efficient star 
formation. This result is also supported by in-house simulations showing that clumps form with 
an initial burst with highly enhanced SFR.
Furthermore, our estimate of the clumps'' lifetime (~ 500 Myr) favours scenarios where they 
survive stellar feedback and confirms that their inward migration is a plausible mechanism to 
form galaxy bulges. 
I will conclude my presentation discussing the analysis of older clumps in our sample. Their age 
distribution as a function of their SFR, specific SFR and distance from the galaxy nucleus, 
respectively put constraints on the star formation history of giant clumps, stellar feedback 
models and inward clumps migration.