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arXiv 0710.0381astro-ph
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星系恒星质量-恒星形成率关系：恒星初始质量函数演化的证据？

The galaxy stellar mass-star formation rate relation: Evidence for an evolving stellar initial mass function?

Romeel Davé

备注：
14 pages, MNRAS, accepted version. Significant expansion of discussion; includes comparisons to new observations
发表信息：
Mon.Not.Roy.Astron.Soc.385:147-160,2008
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摘要：

星系恒星质量-恒星形成率关系（M*-SFR）的演化为星系的恒星质量聚集历史提供了重要的约束条件。对于恒星形成星系，观测到M*-SFR相当紧，从z~0-2开始斜率接近1。星系形成的模拟再现了这些趋势，因为在这些系统中，平滑而稳定的冷吸积占了普遍的主导地位。相比之下，M*-SFR关系的振幅的演变与模型中的明显不同。用恒星形成活动参数α =（M*/SFR）/（t_H-1 Gyr）表示，模型预测α ~1为常数，红移z=4+，而观测到的M*-SFR关系表明，从z~2到今天，α增加了X3。在高z的低α不仅与模型相冲突，而且也很难与高z星系的其他观测相协调。系统偏差可能会显着影响测量的M* 和SFR，但详细的考虑表明，没有明显的候选人来调和的差异。一个投机性的解决方案被认为是在恒星初始质量函数（IMF）的演变更高质量的恒星形成在早期的时代。继Larson之后，研究了一个模型，其中IMF翻转的特征质量Mhat随红移而增加。如果Mhat=0.5（1+z）^2 Mo到z~2，则观测到的和预测的M*-SFR演化可能是一致的。这样的演化与最近对宇宙恒星质量增长的观测结果大致相符，并且由此产生的z=0累积IMF与Fardal等人为了调和观测到的宇宙恒星形成历史与现今化石光测量而青睐的大腹便便IMF相似。[删节]

英文摘要：

The evolution of the galaxy stellar mass--star formation rate relationship (M*-SFR) provides key constraints on the stellar mass assembly histories of galaxies. For star-forming galaxies, M*-SFR is observed to be fairly tight with a slope close to unity from z~0-2. Simulations of galaxy formation reproduce these trends owing to the generic dominance of smooth and steady cold accretion in these systems. In contrast, the amplitude of the M*-SFR relation evolves markedly differently than in models. Stated in terms of a star formation activity parameter alpha=(M*/SFR)/(t_H-1 Gyr), models predict a constant alpha~1 out to redshifts z=4+, while the observed M*-SFR relation indicates that alpha increases by X3 from z~2 until today. The low alpha at high-z not only conflicts with models, but is also difficult to reconcile with other observations of high-z galaxies. Systematic biases could significantly affect measurements of M* and SFR, but detailed considerations suggest that none are obvious candidates to reconcile the discrepancy. A speculative solution is considered in which the stellar initial mass function (IMF) evolves towards more high-mass star formation at earlier epochs. Following Larson, a model is investigated in which the characteristic mass Mhat where the IMF turns over increases with redshift. The observed and predicted M*-SFR evolution may be brought into agreement if Mhat=0.5(1+z)^2 Mo out to z~2. Such evolution broadly matches recent observations of cosmic stellar mass growth, and the resulting z=0 cumulative IMF is similar to the paunchy IMF favored by Fardal et al to reconcile the observed cosmic star formation history with present-day fossil light measures. [abridged]

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