Collapse of Primordial Filamentary Clouds under Far-Ultraviolet Radiation

Abstract

Collapse and fragmentation of primordial filamentary clouds under isotropic dissociation radiation is investigated with one-dimensional hydrodynamical calculations. We investigate the effect of dissociation photon on the filamentary clouds with calculating non-equilibrium chemical reactions. With the external radiation assumed to turn on when the filamentary cloud forms, the filamentary cloud with low initial density ($n_0 \le 10^2 \mathrm{cm^{-3}}$) suffers photodissociation of hydrogen molecules. In such a case, since main coolant is lost, temperature increases adiabatically enough to suppress collapse. As a result, the filamentary cloud fragments into very massive clouds ($\sim 10^5 M_\odot$). On the other hand, the evolution of the filamentary clouds with high initial density ($n_0>10^2 \mathrm{cm^{-3}}$) is hardly affected by the external radiation. This is because the filamentary cloud with high initial density shields itself from the external radiation. It is found that the external radiation increases fragment mass. This result is consistent with previous results with one-zone models. It is also found that fragment mass decreases owing to the external dissociation radiation in the case with sufficiently large line mass.Comment: 26 pages, 15 figures, accepted by PAS