Velocity-coherent substructure in TMC-1: inflow and fragmentation

Abstract

Filamentary structures have been found nearly ubiquitously in molecular clouds and yet their formation and evolution is still poorly understood. We examine a segment of Taurus Molecular Cloud 1 (TMC-1) that appears as a single, narrow filament in continuum emission from dust. We use the Regularized Optimization for Hyper-Spectral Analysis (ROHSA), a Gaussian decomposition algorithm which enforces spatial coherence when fitting multiple velocity components simultaneously over a data cube. We analyze HC5N (9-8) line emission as part of the Green Bank Ammonia Survey (GAS) and identify three velocity-coherent components with ROHSA. The two brightest components extend the length of the filament, while the third component is fainter and clumpier. The brightest component has a prominent transverse velocity gradient of 2.7 ± 0.1 km s−1 pc−1 which we show to be indicative of gravitationally induced inflow. In the second component we identify regularly spaced emission peaks along its length. We show that the local minima between pairs of adjacent HC5N peaks line up closely with submillimetre continuum emission peaks, which we argue is evidence for fragmentation along the spine of TMC-1. While coherent velocity components have been described as separate physical structures in other star-forming filaments, we argue that the two bright components identified in HC5N emission in TMC-1 are tracing two layers in one filament: a lower density outer layer whose material is flowing under gravity towards the higher density inner layer of the filament.

Detection of Interstellar E-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1

“…The resulting molecular abundances, with respect to an assumed N T, H 2 ( ) = 1 × 10 22 cm −2(Gratier et al 2016), were converted to column densities and compared with the observed values. This N T, H 2 ( ) value is consistent with the H 2 column density map of TMC-1 derived from the dust continuum emission observed by Herschel(Smith et al 2023).…”

Magnetic Fields and Fragmentation of Filaments in the Hub of California-X

“…If the inclination to the line of sight is 12°and 35°for Fil1 and Fil2, respectively, the core spacings of Fil1 and Fil2 become 0.64 pc and 0.28 pc, coming close to four times each filament's width. However, the quasiperiodic spacings of fragments in filaments in observations (e.g., Smith et al 2023) and simulations (e.g., Clarke et al 2016) do not always match the expectations of classical cylinder model. Zhang et al (2020) used Herschel far-infrared data and investigated the filaments and cores in the California-X region.…”