Do Environmental Conditions Affect the Dust-Induced Fragmentation in Low-Metallicity Clouds? Effect of Pre-Ionization and Far-Ultraviolet/Cosmic-Ray Fields

We study the effects of the fully ionized initial state, or pre-ionization, on the subsequent thermal evolution of low-metallicity clouds under various intensities of external far-ultraviolet (FUV) and cosmic-ray (CR) fields. Pre-ionization significantly affects the thermal and dynamical evolution of metal-free clouds without FUV/CRs by way of efficient HD formation. On the other hand, the pre-ionization effect on thermal evolution is limited in the very low-density regime for more metal-enriched clouds ([Z/H] greater than or similar to -4), or those under a modest FUV (greater than or similar to 10(-3)) field or CR field (greater than or similar to 0.1) of the present-day galactic disk levels. In any case, for greater than or similar to 10(8) cm(-3), neither the initial ionization state nor the irradiating FUV strength affect the thermal evolution. The dust cooling is an important mechanism for making sub-solar mass fragments in low-metallicity gas. Since this fragmentation occurs at the temperature minimum by dust cooling at greater than or similar to 10(10) cm(-3), this process is not vulnerable either to the initial ionization state or external radiation.