Oral title: Observing the first phases of planet formation: measuring vertical dust settling in Edge-On Disks

Oral abstract: Planets form in Protoplanetary disks. New instruments like ALMA and VLT / SPHERE are revealing features 
in young disks that may be the traces of these planets: rings, gaps, spirals. The direct detection of forming planets still 
located inside their disk remains, however, very challenging.  The consequence is that direct observational constraints on 
the formation mechanism are sparse.
In this talk I will show the results of an on-going survey with ALMA and HST to look for a sample of edge-on disks. The 
ALMA data reveal without ambiguity that vertical dust settling has had a major impact on the dust distribution within the 
disk. Clearly the dust seen by ALMA is located at the disk midplane, in a very thin layer, unresolved even with ALMA's 
longest baselines! This is in sharp opposition from the smaller dust seen by HST in scattered light images and located at 
much higher altitude above the disk midplane.
From these data sets, direct measures of the gas scale height and geometrical thickness of the dust layer can be 
obtained.  Other important quantities like the amount of turbulence, and the gas-to-dust ratio in the disk midplane can be 
derived. 
These observational contraints are critical to inform planet formation theories and models.