Toward a comprehensive understanding of dust distribution in protostellar and planetary disks with ALMA

ABSTRACT :
Planet formation is one of the key questions for astrnomy and has been studied. One of the promissing scenarios of the planet formation would be coagulation of the interstellar dust in disks (e.g., Hayashi 1988). Before ALMA, it has been suggested that the dust grains are indeed grown to be millimeter or centimeter sized pebbles (or even larger) by investigating the dust opacity indices. However, the ALMA high-spatial resolution observations have revealed that the dust opacity measurement no longer traces the dust size under optically thick emission conditions. In contrast, dust polarization, new method to measure the dust size, has shown that the dust size is about only 100 micron. These results may raise a critical issue of the planet formation because the dust grains are not grown to be as large as pebbles. However, the recent multi-bands analysis taking dust polarization and dust opacity index suggests that the dust size may become larger in some specfic regions in the disks such as ring, crescent, and outside of the CO snowline (even though the stokes number is still as low as 0.01). In this talk, I will show some results of the multi-band analysis and some caveats to measure the dust size. I will also discuss possible scenarios of the planet formation.