3.28 μm Feature Mapping in Starburst Galaxies

Abstract

We present narrow-band 3.3 μm infrared images of the central region of the starburst galaxies M82, N3690 and N6240. The images were taken at the Canada-France-Hawaii 3m60 telescope using the CIRCUS IR Camera featuring a 128² InSb detector with pixel size of .25″ or .5″. In all three galaxies, the images, analyzed in terms of Line/Continuum ratio which is sensitive to the relative abundance of the carrier of the line — presumably PAH molecules —, reveal new features: i) in the most active part of the starburst, where the UV density is the highest, the Line/Continuum ratio is small, evidencing partial destruction of PAHs by UV; ii) the Line/Continuum ratio is even smaller or zero at positions and in direction where a superwind or supernova remnants are detected; iii) the Line/Continuum ratio peaks in circum-starburst haloes coinciding with positions where molecular gas (CO and HCN) concentrates: this is the only places where PAH molecules can be sufficiently shielded from hard UV.