AN INCREASING STELLAR BARYON FRACTION IN BRIGHT GALAXIES AT HIGH REDSHIFT
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© 2015. The American Astronomical Society. All rights reserved.. Recent observations have shown that the characteristic luminosity of the rest-frame ultraviolet (UV) luminosity function does not significantly evolve at 4 < z < 7 and is approximately We investigate this apparent non-evolution by examining a sample of 173 bright, MUV < -21 galaxies at z = 4-7, analyzing their stellar populations and host halo masses. Including deep Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that galaxies at z = 4-7 have similar stellar masses of log(M/Mo) = 9.6-9.9 and are thus relatively massive for these high redshifts. However, bright galaxies at z = 4-7 are less massive and have younger inferred ages than similarly bright galaxies at z = 2-3, even though the two populations have similar star formation rates and levels of dust attenuation for a fixed dust-attenuation curve. Matching the abundances of these bright z = 4-7 galaxies to halo mass functions from the Bolshoi ΛCDM simulation implies that the typical halo masses in galaxies decrease from log(Mh/Mo) = 11.9 at z = 4 to log(Mh/Mo) = 11.4 at z = 7. Thus, although we are studying galaxies at a similar stellar mass across multiple redshifts, these galaxies live in lower mass halos at higher redshift. The stellar baryon fraction in galaxies in units of the cosmic mean Ωb/Ωm rises from 5.1% at z = 4 to 11.7% at z = 7; this evolution is significant at the ∼3σ level. This rise does not agree with simple expectations of how galaxies grow, and implies that some effect, perhaps a diminishing efficiency of feedback, is allowing a higher fraction of available baryons to be converted into stars at high redshifts.
author list (cited authors)
Finkelstein, S. L., Song, M., Behroozi, P., Somerville, R. S., Papovich, C., Milosavljević, M., ... Willner, S. P.