Spitzer IRAC and MIPS Imaging of Clusters and Outflows in 9 High-mass Star Forming Regions

Abstract

We present Spitzer Space Telescope IRAC and MIPS observations toward a sample of nine high-mass star forming regions at a distance of around 2 kpc. Based on IRAC and MIPS 24 $μ$m photometric results and 2MASS JHKs data, we carry out a census of young stellar objects (YSOs) in a 5' by 5' field toward each region. Toward seven out of the nine regions, we detect parsec sized clusters with around 20 YSOs surrounded by a more extended and sparse distribution of young stars and protostars. For the other two regions, IRAS 20126+4104 and IRAS 22172+5549, the former has the lowest number of YSOs in the sample and shows no obvious cluster, and the latter appears to be part of a larger, potentially more evolved cluster. The deep IRAC imaging reveals at least twelve outflows in eight out of the nine regions, with nine outflows prominent in the 4.5 $μ$m band most probably attributed to shocked H$_2$ emission, two outflows dominated by scattered light in the 3.6 and 4.5 $μ$m bands, and one outflow standing out from its hydrocarbon emission in the 8.0 $μ$m band. In comparison with previous ground-based observations, our IRAC observations reveal new outflow structures in five regions. The dramatically different morphologies of detected outflows can be tentatively interpreted in terms of possible evolution of massive outflows. The driving sources of these outflows are deeply embedded in dense dusty cores revealed by previous millimeter interferometric observations. We detect infrared counterparts of these dusty cores in the IRAC or MIPS 24 $μ$m bands. Reflection nebulae dominated by the emission from UV heated hydrocarbons in the 8 $μ$m band can be found in most regions and they may imply the presence of young B stars.