The disk around the Herbig Ae/Be star HD 100546 has been extensively studied and it is one of the systems for which there are observational indications of ongoing and/or recent planet formation .
However , up until now no resolved image of the millimeter dust emission or the gas has been published .
We present the first resolved images of the disk around HD 100546 obtained in Band 7 with the ALMA observatory .
The CO ( 3–2 ) image reveals a gas disk that extends out to 350 au radius at the 3- \sigma level .
Surprisingly , the 870 \mu m dust continuum emission is compact ( radius < 60 au ) and asymmetric .
The dust emission is well matched by a truncated disk with outer radius of \approx 50 au .
The lack of millimeter-sized particles outside the 60 au is consistent with radial drift of particles of this size .
The protoplanet candidate , identified in previous high-contrast NACO/VLT L ^ { \prime } observations , could be related to the sharp outer edge of the millimeter-sized particles .
Future higher angular resolution ALMA observations are needed to determine the detailed properties of the millimeter emission and the gas kinematics in the inner region ( < 2 \arcsec ) .
Such observations could also reveal the presence of a planet through the detection of circumplanetary disk material .