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Title:
The Role of the First Metals in Forming the Second Stars
Authors:
Smith, Britton; Sigurdsson, Steinn; O'Shea, Brian; Norman, Michael
Affiliation:
AA(Department of Astronomy & Astrophysics, The Pennsylvania State University, University Park, PA), AB(Department of Astronomy & Astrophysics, The Pennsylvania State University, University Park, PA), AC(Los Alamos National Laboratory, Los Alamos, NM), AD(Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA)
Publication:
FIRST STARS III: First Stars II Conference. AIP Conference Proceedings, Volume 990, pp. 73-75 (2008). (AIPC Homepage)
Publication Date:
03/2008
Origin:
AIP
PACS Keywords:
Star formation, Population III stars, Numerical simulation; solution of equations, Background radiations, Molecular clouds, H2 clouds, dense clouds, and dark clouds
DOI:
10.1063/1.2905676
Bibliographic Code:
2008AIPC..990...73S

Abstract

Numerical simulations of the formation of pop III stars suggest that they were much more massive than the pop II and pop I stars observed today. This is due to the collapse dynamics of metal-free gas, which is regulated by the radiative cooling properties of molecular hydrogen. We study how the collapse of gas-clouds is altered by the addition of metals to the star-forming environment. We perform a series of numerical simulations of pre-enriched star-formation at various metallicities using the adaptive mesh refinement, hydrodynamic + N-body code, Enzo. For metallicities below the critical metallicity, Zcr, collapse proceeds nearly identical to the metal-free case, and only massive, singular objects form. For metallicities well above Zcr, efficient cooling rapidly lowers the gas temperature to the temperature of the cosmic microwave background (CMB), which is significantly higher in the distant past. The gas is physically unable to radiatively cool below the CMB temperature, and thus, becomes very thermally stable. For moderately high metallicities, Z>=10-3.5 Zsolar, this occurs early in the evolution of the gas-cloud, when the central density is still relatively low. The resulting cloud-cores show little or no fragmentation, and have mass-scales of a few hundred Msolar. On the other hand, if the metallicity is only slightly above Zcr, the cloud slowly cools without ever reaching the CMB temperature. In this case, the minimum cloud temperature is achieved at much higher densities than in the high-metallicity case, resulting in mass-scales of just a few Msolar.
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