NIKA2 maps tracing dust grain evolution in cores of TMC1

The Taurus Molecular Cloud TMC1 is a nearby molecular cloud filament exhibiting several dense cores. It has been intensely studied in particular because of its very rich gas phase chemistry. Here, we present NIKA2 observations with the IRAM 30m telescope of its dust emission at 1 and 2mm wavelengths. Its vicinity of only 140 pc allows to study variations of its grain properties, i.e. its dust emissivity index β, on scales of only 2430 a.u. (18″). The NIKA2 maps are combined with Planck data to retrieve the emission at scales larger than the NIKA2 field-of-view. Maps of the 1mm/2mm flux ratio are then combined with a dust temperature map derived from Herschel data to create a map of the β index. Several of the observed cores exhibit a significant increase of β from ~ 1.2 in the outskirts at optical extinctions of ~ 5 mag to ~ 1.8 in the centers at ~ 18 mag. Grain models show that this steepening of the mm/submm emissivity is consistent with the gradual build-up of ice layers on the grain surfaces due to freeze-out of molecules in the cold, dense interiors of these cores.