line mass or mass per unit length (i.e., $M_{\rm line,obs}$ $\sim$3000 M$_{\odot}$ pc$^{-1}$) and the critical line mass ($M_{\rm line,crit}$) of the filament “fs1". Due to unknown inclination angle of the filament, we consider the observed line mass as an upper limit. The expression of $M_{\rm line,crit}$ is given by $\sim$16 M$_{\odot}$ pc$^{-1}$ $\times$ (T$_{gas}$/10 K) for a gas filament, assuming that the filament is an infinitely extended, self-gravitating and isothermal cylinder without magnetic support [e.g. @ostriker64; @inutsuka97; @andre14]. The value of $M_{\rm line,obs}$ can be compared against the critical line mass $M_{\rm line,crit}$ of 16–32 M$_{\odot}$ pc$^{-1}$ at T = 10–20 K, suggesting that the filament “fs1" is thermally supercritical. In general, the thermally supercritical filaments are believed to be unstable to radial gravitational collapse and fragmentation [e.g., @andre10].

Star Formation Activities {#sec:sf}
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In this section, to examine the ongoing SF activities, we have identified Class I YSOs in our selected target area around the W33 complex. In this context, the color-color plot (\[4.5\]$-$\[5.8\] vs \[3.6\]$-$\[4.5\]) is employed (not shown here), and the infrared color conditions (i.e., \[4.5\]$-$\[5.8\] $\ge$ 0.7 mag and \[3.6\]$-$\[4.5\] $\ge$ 0.7 mag) are adopted to depict Class I YSOs [see @hartmann05; @getman07; @dewangan17b; @dewangan18b; 