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Recent observational and theoretical investigations have emphasised theimportance of filamentary networks within molecular clouds as sites of starformation. Since such environments are more complex than those of isolatedcores, it is essential to understand how the observed line profiles fromcollapsing cores with non-spherical geometry are affected by filaments. In thisstudy, we investigate line profile asymmetries by performing radiative transfercalculations on hydrodynamic models of three collapsing cores that are embeddedin filaments. We compare the results to those that are expected for isolatedcores. We model the five lowest rotational transition line (J = 1-0, 2-1, 3-2,4-3, and 5-4) of both optically thick (HCN, HCO$^+$) as well as optically thin(N$_2$H$^+$, H$^{13}$CO$^+$) molecules using constant abundance laws. We findthat less than 50% of simulated (1-0) transition lines show blue infallasymmetries due to obscuration by the surrounding filament. However, thefraction of collapsing cores that have a blue asymmetric emission line profilerises to 90% when observed in the (4-3) transition. Since the densest gastowards the collapsing core can excite higher rotational states, upper leveltransitions are more likely to produce blue asymmetric emission profiles. Weconclude that even in irregular, embedded cores one can trace infalling gasmotions with blue asymmetric line profiles of optically thick lines byobserving higher transitions. The best tracer of collapse motions of our sampleis the (4-3) transition of HCN, but the (3-2) and (5-4) transitions of both HCNand HCO$^+$ are also good tracers.

Line Profiles of Cores within Clusters. III. What is the most reliable tracer of core collapse in dense clusters?