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Evolution of the first supernovae in protogalaxies: Dynamics of mixing of heavy elements |
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| Authors: | E O Vasiliev E I Vorobyov E E Matvienko A O Razoumov Yu A Shchekinov |
| Institution: | 1. Physics Research Institute, Southern Federal University, Roston-on-Don, Russia 2. Physics Department, Southern Federal University, Roston-on-Don, Russia 3. Institute of Astronomy, University of Vienna, Vienna, Austria 4. SHARCNET/UOIT Consortium, Oshawa, Ontario, Canada |
| Abstract: | The paper considers the evolution of the supernova envelopes produced by Population III stars with masses ofM * ?? 25?C200M ?? located in non-rotating protogalaxies with masses of M ?? 107 M ?? at redshifts z = 12, with dark-matter density profiles in the form of modified isothermal spheres. The supernova explosion occurs in the ionization zone formed by a single parent star. The properties of the distribution of heavy elements (metals) produced by the parent star are investigated, as well as the efficiency with which they are mixed with the primordial gas in the supernova envelope. In supernovae with high energies (E ? 5 × 1052 erg), an appreciable fraction of the gas can be ejected from the protogalaxy, but nearly all the heavy elements remain in the protogalaxy. In explosions with lower energies (E ? 3 × 1052 erg), essentially no gas and heavy elements are lost from the protogalaxy: during the first one to threemillion years, the gas and heavy elements are actively carried from the central region of the protogalaxy (r ?? 0.1r v , where r v is the virial radius of the protogalaxy), but an appreciable fraction of the mass of metals subsequently returns when the hot cavity cools and the envelope collapses. Supernovae with high energies (E ? 5 × 1052 erg) are characterized by a very low efficiency of mixing of metals; their heavy elements are located in the small volume occupied by the disrupted envelope (in a volume comparable with that of the entire envelope), with most of the metals remaining inside the hot, rarified cavity of the envelope. At the same time, the efficiency of mixing of heavy elements in less energetic supernovae (E ? 3 × 1052 erg) is appreciably higher. This comes about due to the disruption of the hot cavity during the collapse of the supernova envelope. However, even in this case, a clear spatial separation of regions enriched and not enriched in metals is visible. During the collapse of the supernova envelope, the metallicity of the gas is appreciably higher in the central region (Z] ?? ?1 to 0) than at the periphery (Z] ?? ?2 to ?4) of the protogalaxy; most of the enriched gas has metallicities Z] ?? ?3.5 to ?2.5. The masses of enriched fragments of the supernova envelope remain appreciably lower than the Jeans mass, except in regions at the center of the protogalaxy upon which the surrounding enriched gas is efficiently accreted. Consequently, the birth of stars with metallicities close to those characteristic of present-day Galactic stars is very probable in the central region of the protogalaxy. |
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