paper

The Odd Meanderings of the IMF Across Cosmic Time

arXiv:1008.5283

Abstract

It is difficult to reconcile the observed evolution of the star formation rate versus stellar mass (SFR-M*) relation with expectations from current hierarchical galaxy formation models. The observed SFR-M* relation shows a rapid rise in SFR(M*) from z=0-2, and then a surprisingly lack of amplitude evolution out to z~6+. Hierarchical models of galaxy formation match this trend qualitatively but not quantitatively, with a maximum discrepancy of ~x3 in SFR at z~2. One explanation, albeit radical, is that the IMF becomes modestly weighted towards massive stars out to z~2, and then evolves back towards its present-day form by z~4 or so. We observe that this redshift trend mimics that of the cosmic fraction of obscured star formation, perhaps hinting at a physical connection. Such IMF evolution would concurrently go towards explaining persistent discrepancies between integrated measures of star formation and present-day stellar mass or cosmic colors.

arXiv comment8 pages, in proceedings of "UP2010: Have Observations Revealed a Variable Upper End of the Initial Mass Function?", M. Treyer, J.C. Lee, M.H. Seibert, T. Wyder, J. Neil, eds

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