A study of the massive star-forming region M8 using images from the Spitzer Infrared Array Camera

We present photometry and images (3.6, 4.5, 5.8 and 8.0 mu m) from the Spitzer Infrared Array Camera (IRAC) of the star-forming region Messier 8 (M8). The IRAC photometry reveals ongoing star formation in the M8 complex, with 64 class 0/I and 168 class II sources identified in several locations in the vicinity of submm gas cores/clumps. Nearly 60 per cent of these young stellar objects (YSOs) occur in about seven small clusters. The spatial surface density of the clustered YSOs is determined to be about 10-20 YSOs pc-2. Fresh star formation by the process of 'collect and collapse' might have been triggered by the expanding H ii regions and winds from massive stars. IRAC ratio images are generated and studied in order to identify possible diagnostic emission regions in M8. The image of 4.5/8.0 mu m reveals a Br alpha counterpart of the optical Hourglass H ii region, while the ratio 8.0/4.5 mu m indicates PAH emission in a cavity-like structure to the east of the Hourglass. The ratio maps of 3.6/4.5, 5.8/4.5 and 8.0/4.5 mu m seem to identify PAH emission regions in the sharp ridges and filamentary structures seen east to west and north-east to south-west in the M8 complex.