Intergalactic medium metal enrichment through dust sputtering |
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| Authors: | Simone Bianchi Andrea Ferrara |
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| Institution: | Istituto di Radioastronomia/CNR - Sezione di Firenze, Largo Enrico Fermi 5, 50125 Firenze, Italy;SISSA/International School for Advanced Studies, via Beirut 2-4, 34013 Trieste, Italy |
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| Abstract: | We study the motion of dust grains into the intergalactic medium (IGM) around redshift z = 3 , to test the hypothesis that grains can efficiently pollute the gas with metals through sputtering. We use the results available in the literature for radiation-driven dust ejection from galaxies as initial conditions and follow the motion onwards. Via this mechanism, grains are ejected into the IGM with velocities >100 km s?1 ; as they move supersonically, grains can be efficiently eroded by non-thermal sputtering. However, Coulomb and collisional drag forces effectively reduce the charged grain velocity. Up-to-date sputtering yields for graphite and silicate (olivine) grains have been derived using the code transport of ions in matter ( trim ), for which we provide analytic fits. After training our method on a homogeneous density case, we analyse the grain motion and sputtering in the IGM density field as derived from a Λ cold dark matter (CDM) cosmological simulation at z = 3.27 . We found that only large ( a ? 0.1μm) grains can travel up to considerable distances (few ×100 kpc physical) before being stopped. Resulting metallicities show a well-defined trend with overdensity δ. The maximum metallicities are reached for 10 < δ < 100 corresponding to systems, in quasi-stellar object (QSO) absorption spectra, with 14.5 < log N (H i ) < 16 ]. However the distribution of sputtered metals is very inhomogeneous, with only a small fraction of the IGM volume polluted by dust sputtering (filling factors of 18 per cent for Si and 6 per cent for C). For the adopted size distribution, grains are never completely destroyed; nevertheless, the extinction and gas photoelectric heating effects resulting from this population of intergalactic grains are well below current detection limits. |
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| Keywords: | dust extinction intergalactic medium cosmology: miscellaneous |
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