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Evidence of Cosmic Evolution of the Stellar Initial Mass Function
Ist Teil von
The Astrophysical journal, 2008-02, Vol.674 (1), p.29-50
Ort / Verlag
Chicago, IL: IOP Publishing
Erscheinungsjahr
2008
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
Theoretical arguments and indirect observational evidence suggest that the stellar IMF may evolve with time, such that it is more weighted toward high-mass stars at higher redshift. Here we test this idea by comparing the rate of luminosity evolution of massive early-type galaxies in clusters at 0.02 , z , 0.83 to the rate of their color evolution. A combined fit to the rest-frame U - V color evolution and the previously measured evolution of the M/L(B ratio gives x = -0.3(+(-(0(0(.(.(4(7 for the logarithmic slope of the IMF in the region around 1 M [unk], significantly flatter than the present-day value in the Milky Way disk of x = 1.3c0.3. The best-fitting luminosity-weighted formation redshift of the stars in massive cluster galaxies is 3.7(+(-(2(0(.(.(3(8, and a possible Interpretation is that the characteristic mass m(x) had a value of 62 M [unk] at z 6 4 (compared to m(e) 6 0.1 M [unk] today), in qualitative agreement with models in which the characteristic mass is a function of the Jeans mass in molecular clouds. Such a "bottom-light" IMF for massive cluster galaxies has significant implications for the interpretation of measurements of galaxy formation and evolution. Applying a simple form of IMF evolution to literature data, we find that the volume-averaged SFR at high redshift may have been overestimated (by a factor of 3-4 at z > 4), and the cosmic star formation history may have a fairly well defined peak at z61.5. The M/L(v ratios of galaxies are less affected than their SFRs, and future data on the stellar mass density at z > 3 will provide further constraints on IMF evolution. The formal errors likely underestimate the uncertainties, and confirmation of these results requires a larger sample of clusters and the Inclusion of redder rest-frame colors in the analysis.