Stars form in dense cores within molecular clouds. The cores are characterised by higher density and lower temperatures than its natal cloud (Myers,1983). The turbulence inside cores is subsonic (Barranco & Goodman, 1998), in contrast to supersonic linewidths in the surrounding cloud (Larson, 1981). Observations show that the transition to coherence at the core-cloud boundary is sharp (Pineda et al., 2010). Therefore, cores are currently understood to be isolated units of star formation, well-separated from its surrounding molecular cloud. However, this transition has not been studied with high sensitivity in the vicinity of the cores.
Our recent study showed substantial amount of subsonic material outside the typically derived core boundaries (Choudhury et al., 2021), indicating that the cores are not completely isolated from their natal cloud. This implies that further accretion by the core is possible during its evolution, suggesting a need to update of the current models of structure and dynamical evolution of dense core. The extent and spatial distribution of the subsonic material outside the core boundary will help us understand how the core is connected to the surrounding gas, which will also help shed light on the dissipation of turbulence, which is an important step in core formation.
We present high-sensitivity NH3 observations of a prestellar core H-MM1 in Ophiuchus. We fit two spatially resolved components towards the neighbourhood of the core, thereby separating the core and cloud components in the line of sight (Choudhury et al, 2020). We map the subsonic emission outside the dense core boundary. We find that the distribution of the subsonic material around the core is not uniform, rather, highly directional, suggesting that the core might be connected to the filamentary substructures present in L1688 (Ladjelate et al., 2020), and accrete material from its surrounding (similar to streamers; Pineda et al., 2020).