tokens: NW part of RCW 57A. This could be the plausible reason behind the low-density material observed in the NW region. The observed large-scale loops in the NE possibly formed due to the newly formed material as a result of the expanding I-fronts driven by the embedded massive protostars of RCW 57A. A high-velocity outflow signature is discernible close to eastward from the center, while the same feature is absent westward as shown in Figure 11 (b). This could be attributed to the confined ionized gas flow toward the west from the center, possibly due to the presence of a dense clump (thin black contours in Figure 7 ). The high-velocity component is only seen toward the east, which implies a dearth of dense material there, and hence, the ionized gas expanded with relatively more velocity. de Pree et al. ( 1999 ) and Purcell et al. ( 2009 ) have also shown that the H ii region expands more freely toward the east and is bounded on the west. 5.2. Column Density Profiles: Filament Width and <italic>B</italic>-field Support We fitted a Gaussian to the mean column density profiles spread over ∼5 pc radii, and the resultant FWHM, corresponding to the filament characteristic width, is found to be 1.55 ± 0.09 pc. However, a constant filament width of ∼0.1 pc was determined for the central dense sections of the filaments of nearby star-forming regions in the Herschel Gould Belt survey by fitting a Gaussian to the inner sections (radii up to 0.3–0.4 pc) of the filaments (Arzoumanian et al. 2011 ). Therefore, we fit a Gaussian to the inner 1 pc width of the clubbed mean column density profiles of the NW and SE regions, and the resultant σ and FWHM are found to be 0.21 ± 0.08 pc and 0.50 ± 0.18 pc, respectively. Within the error, the filament width (0.50 pc; green lines in Figures 12 (a) and (b)) of RCW 57A is higher than the constant filament width of ∼0.1 pc (Arzoumanian et al. 2011 ). Filament widths larger than 0.1 pc (spanning over 0.1 –1 pc with typical widths of ∼0.2–0.3 pc) have also been witnessed in a number of studies (e.g., Hennemann et al. 2012 ; Juvela et al. 2012 ). However, the filament width of RCW 57A has not been resolved because of the limited resolution (364 corresponds to 0.42 pc as shown by the cyan lines) of the column density map. The mean power-law index p = 2.02 ± 0.05, derived from the Plummer-like profile fitting for RCW 57A, is consistent with other studies (Arzoumanian et al. 2011 ; Juvela et al. 2012 ; Palmeirim et al. 2013 ; Hoq et al. 2017 ). A similar value of this index ( p = 2) is expected if the filament is supported by B -fields (Hennebelle 2003 ; Tilley Pudritz 2003 ), in accordance with our observational results supporting the active role of B -fields in the formation and evolution of filaments, as described in Section 5.3 below. 5.3. Evolutionary Scenario of the Filament and Bipolar Bubble Based on the morphological correlations among the (i) dense filamentary cloud structure seen in the submillimeter (in the 0.87 mm
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