Consequences of cosmic microwave background-regulated star formation

Abstract

It has been hypothesized that the cosmic microwave background (CMB) provides a temperature floor for collapsing protostars that can regulate the process of star formation and result in a top-heavy initial mass function at high metallicity and high redshift. We examine whether this hypothesis has any testable observational consequences. First we determine, using a set of hydrodynamic galaxy formation simulations, that the CMB temperature floor would have influenced the majority of stars formed at redshifts between z=3 and 6, and probably even to higher redshift. Five signatures of CMB-regulated star formation are: (1) a higher supernova rate than currently predicted at high redshift; (2) a systematic discrepancy between direct and indirect measurements of the high redshift star formation rate; (3) a lack of surviving globular clusters that formed at high metallicity and high redshift; (4) a more rapid rise in the metallicity of cosmic gas than is predicted by current simulations; and (5) an enhancement in the abundances of alpha elements such as O and Mg at metallicities -2 < [Fe/H] < -0.5. Observations are not presently able to either confirm or rule out the presence of these signatures. However, if correct, the top-heavy IMF of high-redshift high-metallicity globular clusters could provide an explanation for the observed bimodality of their metallicity distribution.

ApJ in press, 10 pages, emulateapj

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• De Re Metallica: The cosmic chemical evolution of galaxies
• Mass-metallicity relation from z=5 to the present: Evidence for a transition in the mode of galaxy growth at z=2.6 due to the end of sustained primordial gas infall
• Star Formation in the First Galaxies - II: Clustered Star Formation and the Influence of Metal Line Cooling
• Impact of the cosmic background radiation on the initial mass function of metal-poor stars
• Cosmological Galaxy Evolution with Superbubble Feedback II: The Limits of Supernovae
• Fragmentation in the First Galaxies
• The Cosmic Microwave Background and the Stellar Initial Mass Function
• On the inconsistency between the estimates of cosmic star formation rate and stellar mass density of high redshift galaxies
• Stellar Initial Mass Function over a range of redshifts