An AKARI infrared study of dust emission in Galactic bubbles indicative of large-scale cloud–cloud collisions

Abstract

We report our systematic study on dust emission in massive star-forming regions indicative of large-scale cloud–cloud collisions, using the AKARI infrared (IR) all-sky survey data at wavelengths of 9, 18, 65, 90, 140, and 160μm. We focus on the Galactic bubbles catalogued by Spitzer, which are categorized into two types of morphology, closed and broken bubbles. A broken bubble has a possibility of being created by a cloud–cloud collision, judging from its morphological similarity to the structure theoretically predicted as a product of the collision. Therefore we search for systematic differences in IR properties between the two types. We performed aperture photometry for 111 Spitzer bubbles and created the spectral energy distribution (SED) of each bubble. We decomposed the SED into polycyclic aromatic hydrocarbon (PAH), warm and cold dust components by model fitting, and calculated their luminosities, LPAH, Lwarm and Lcold respectively, by integrating each SED component as a function of the wavelength. We then investigated the total IR luminosity (LTIR=LPAH+Lwarm+Lcold), the ratio of LPAH to LTIR and the ratio of Lwarm to LTIR as a function of the bubble radius. As a result, we find systematic differences between the closed and broken bubbles for the former two relations. We discuss the implications of the differences for the scenario of the large-scale cloud–cloud collisions.