We present a multi-wavelength investigation of a large-scale physical system containing the W33 complex .
The extended system ( \sim 50 pc \times 37 pc ) is selected based on the distribution of molecular gas at [ 29.6 , 60.2 ] km s ^ { -1 } and of 88 ATLASGAL 870 \mu m dust clumps at d \sim 2.6 kpc .
The extended system/molecular cloud traced in the maps of ^ { 13 } CO and C ^ { 18 } O emission contains several H ii regions excited by OB stars ( age \sim 0.3–1.0 Myr ) and a thermally supercritical filament ( “ fs1 ” , length \sim 17 pc ) .
The filament , devoid of the ionized gas , shows dust temperature ( T _ { d } ) of \sim 19 K , while the H ii regions are depicted with T _ { d } of \sim 21–29 K. It suggests the existence of two distinct environments in the cloud .
The distribution of Class I young stellar objects ( mean age \sim 0.44 Myr ) traces the early stage of star formation ( SF ) toward the cloud .
At least three velocity components ( around 35 , 45 , and 53 km s ^ { -1 } ) are investigated toward the system .
The analysis of ^ { 13 } CO and C ^ { 18 } O reveals the spatial and velocity connections of cloud components around 35 and 53 km s ^ { -1 } .
The observed positions of previously known sources , W33 Main , W33 A and O4-7I stars , are found toward a complementary distribution of these two cloud components .
The filament “ fs1 ” and a previously known object W33 B are seen toward the overlapping areas of the clouds , where ongoing SF activity is evident .
A scenario concerning the converging/colliding flows from two different velocity components appears to explain well the observed signposts of SF activities in the system .