Physical environment of massive star-forming region W42
  We present an analysis of multi-wavelength observations from various datasets
and Galactic plane surveys to study the star formation process in the W42
complex. A bipolar appearance of W42 complex is evident due to the ionizing
feedback from the O5-O6 type star in a medium that is highly inhomogeneous. The
VLT/NACO adaptive-optics K and L' images (resolutions ~0".2-0".1) resolved this
ionizing source into multiple point-like sources below ~5000 AU scale. The
position angle ~15 deg of W42 molecular cloud is consistent with the H-band
starlight mean polarization angle which in turn is close to the Galactic
magnetic field, suggesting the influence of Galactic field on the evolution of
the W42 molecular cloud. Herschel sub-millimeter data analysis reveals three
clumps located along the waist axis of the bipolar nebula, with the peak column
densities of ~3-5 x10^{22} cm^{-2} corresponding to visual extinctions of AV
~32-53.5 mag. The Herschel temperature map traces a temperature gradient in
W42, revealing regions of 20 K, 25 K, and 30-36 K. Herschel maps reveal
embedded filaments (length ~1-3 pc) which appear to be radially pointed to the
denser clump associated with the O5-O6 star, forming a hub-filament system. 512
candidate young stellar objects (YSOs) are identified in the complex, ~40% of
which are present in clusters distributed mainly within the molecular cloud
including the Herschel filaments. Our datasets suggest that the YSO clusters
including the massive stars are located at the junction of the filaments,
similar to those seen in Rosette Molecular Cloud.
