Fate of clumps in damped Ly$\alpha$ systems

Abstract

Recent observations have revealed that damped Ly$\alpha$ clouds (DLAs) host star formation activity. In order to examine if such star formation activity can be triggered by ionization fronts, we perform high-resolution hydrodynamics and radiative transfer simulations of the effect of radiative feedback from propagating ionization fronts on high-density clumps. We examine two sources of ultraviolet (UV) radiation field to which high-redshift (z ~ 3) galaxies could be exposed: one corresponding to the UV radiation originating from stars within the DLA, itself, and the other corresponding to the UV background radiation. We find that, for larger clouds, the propagating I-fronts created by local stellar sources can trigger cooling instability and collapse of significant part, up to 85%, of the cloud, creating conditions for star formation in a timescale of a few Myr. The passage of the I-front also triggers collapse of smaller clumps (with radii below ~4 pc), but in these cases the resulting cold and dense gas does not reach conditions conducive to star formation. Assuming that 85% of the gas initially in the clump is converted into stars, we obtain a star formation rate of $\sim 0.25M_{\odot }{yr}^{-1}{kpc}^{-2}$. This is somewhat higher than the value derived from recent observations. On the other hand, the background UV radiation which has harder spectrum fails to trigger cooling and collapse. Instead, the hard photons which have long mean-free-path heat the dense clumps, which as a result expand and essentially dissolve in the ambient medium. Therefore, the star formation activity in DLAs is strongly regulated by the radiative feedback, both from the external UV background and internal stellar sources and we predict quiescent evolution of DLAs (not starburst-like evolution).

8 pages, 12 figures, replaced to match the published version in MNRAS

References in corpus (8)

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• The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems
• Minihalo photoevaporation during cosmic reionization: evaporation times and photon consumption rates
• CII* Absorption in Damped Lyman Alpha Systems: (I) Star Formation Rates in a Two-Phase Medium
• Effects of dust grains on early galaxy evolution
• Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift
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Cited by in corpus (4)

• The Physics of the Intergalactic Medium
• Cosmological Radiative Transfer Codes Comparison Project I: The Static Density Field Tests
• Cosmological Radiative Transfer Comparison Project II: The Radiation-Hydrodynamic Tests
• On the relative importance of different microphysics on the D-type expansion of galactic HII regions