Observations of the Near- to Mid-Infrared Unidentified Emission Bands in the Interstellar Medium of the Large Magellanic Cloud

Tamami I. Mori; Itsuki Sakon; Takashi Onaka; Hidehiro Kaneda; Hideki Umehata; Ryou Ohsawa

doi:10.1088/0004-637X/744/1/68

paper

Observations of the Near- to Mid-Infrared Unidentified Emission Bands in the Interstellar Medium of the Large Magellanic Cloud

arXiv:1109.3512 · doi:10.1088/0004-637X/744/1/68

Abstract

We present the results of near- to mid-infrared slit spectroscopic observations (2.55--13.4 um) of the diffuse emission toward nine positions in the Large Magellanic Cloud with the Infrared Camera (IRC) on board AKARI. The target positions are selected to cover a wide range of the intensity of the incident radiation field. The unidentified infrared bands at 3.3, 6.2, 7.7, 8.6 and 11.3 um are detected toward all the targets, and ionized gas signatures: hydrogen recombination lines and ionic forbidden lines toward three of them. We classify the targets into two groups: those without the ionized gas signatures (Group A) and those with the ionized signatures (Group B). Group A includes molecular clouds and photo-dissociation regions, whereas Group B consists of HII regions. In Group A, the band ratios of I(3.3)/I(11.3), I(6.2)/I(11.3), I(7.7)/ $I (11.3) an d$ I(8.6)/ $I (11.3) s h o w p os i t i v ecor r e l a t i o n w i t h t h e I R A S an d A K A R I co l or s, b u tt h oseo f G r o u pB d o n o t f o l l o w t h ecor r e l a t i o n . W e d i sc u ss t h er es u l t s in t er m so f t h e p o l y cy c l i c a r o ma t i c h y d r oc a r b o n (P A H) m o d e l an d a tt r ib u t e t h e d i f f er e n ce t o t h e d es t r u c t i o n o f s ma l l P A H s an d anin cr e a se in t h er eco mbina t i o n d u e t o t h e hi g h e l ec t r o n d e n s i t y in G r o u pB . I n t h e p r ese n t s t u d y, t h e 3.3 u mban d p r o v i d escr u c ia l in f or ma t i o n o n t h es i z e d i s t r ib u t i o nan d / or t h ee x c i t a t i o n co n d i t i o n so f P A H s an d pl a y s ak ey r o l e in t h e d i s t in c t i o n o f G r o u p A f r o m B . T h er es u l t ss ug g es tt h e p oss ibi l i t y o f t h e d ia g r am o f I (3.3) / I (11.3) v . s .$ I(7.7)/$I(11.3) as an efficient diagnostic tool to infer the physical conditions of the interstellar medium.

51 pages, 7 figures, accepted for publication in ApJ

Observations of the Near- to Mid-Infrared Unidentified Emission Bands in the Interstellar Medium of the Large Magellanic Cloud

Abstract

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