Different molecular filament widths as tracers of accretion on to filaments

Abstract

ABSTRACT We explore how dense filament widths, when measured using different molecular species, may change as a consequence of gas accretion towards the filament. As a gas parcel falls into the filament, it will experience different density, temperature, and extinction values. The rate at which this environment changes will affect differently the abundance of different molecules. So, a molecule that forms quickly will better reflect the local physical conditions a gas parcel experiences than a slower forming molecule. Since these differences depend on how the respective time-scales compare, the different molecular distributions should reflect how rapidly the environment changes, i.e. the accretion rate towards the filament. We find that the filament widths measured from time-dependent abundances for C2H, CO, CN, CS, and C3H2 are the most sensitive to this effect. This is because these molecules are the ones presenting also the wider filament widths. On the contrary, molecules such as N2H+, NH3, H2CO, HNC, and CH3OH are not so sensitive to accretion and present the narrowest filament widths. We propose that ratios of filament widths for different tracers could be a useful tool to estimate the accretion rate on to the filament.