We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects ( MHOs ) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows .
We have detected a total of 236 MHOs , 156 of which are new detections , in 22 out of the 26 regions .
We use H _ { 2 } 2.12- \mu m/H _ { 2 } 2.25- \mu m flux ratios , together with morphology , to separate the signatures of fluorescence associated with photo-dissociation regions ( PDRs ) from shocks associated with outflows in order to identify the MHOs .
PDRs have typical low flux ratios of \sim 1.5 - 3 , while the vast majority of MHOs display flux ratios typical of C-type shocks ( \sim 6-20 ) .
A few MHOs exhibit flux ratios consistent with expected values for J-type shocks ( \sim 3-4 ) , but these are located in regions that may be contaminated with fluorescent emission .
Some previously reported MHOs have low flux ratios , and are likely parts of PDRs rather than shocks indicative of outflows .
We identify a total of 36 outflows across the 22 target regions where MHOs were detected .
In over half these regions , MHO arrangements and fluorescent structures trace features present in CO outflow maps , suggesting the CO emission traces a combination of dynamical effects , which may include gas entrained in expanding PDRs as well as bipolar outflows .
Where possible , we link MHO complexes to distinct outflows and identify candidate driving sources .