Keywords: ISM: H II regions — infrared: stars – stars: formation – infrared: ISM: continuum – ISM: individual(W 51 A, G49.5-0.4, G49.4-0.3)

1. INTRODUCTION

2. OBSERVATIONS AND DATA REDUCTION

3.1. G49.5-0.4

3.2. G49.4-0.3

4. DATA ANALYSIS

4.2. Physical Properties of Extended Sources: Kinematic Status and Global History

5. SUMMARY