Stellar Mass—Halo Mass Relation and Star Formation Efficiency in High-Mass Halos

摘要

We study relation between stellar mass and halo mass for high-mass halosusing a sample of galaxy clusters with accurate measurements of stellar massesfrom optical and IR data and total masses from X-ray observations. We find thatstellar mass of the brightest cluster galaxies (BCGs) scales as M*BCGproptoM500^a_BCG with the best fit slope of a_BCG~0.35+-0.1 and scatter of M*BCG at afixed M500 of ~0.2 dex. We show that M*-M relations from abundance matching orhalo modelling reported in recent studies underestimate stellar masses of BCGsby a factor of ~2-4, because these studies used stellar mass functions (SMF)based on photometry that severely underestimates the outer surface brightnessprofiles of massive galaxies. We show that M*-M relation derived usingabundance matching with the recent SMF calibration by Bernardi et al. (2013)based on improved photometry is in a much better agreement with the relation wederive. The total stellar mass of galaxies correlates with total mass M500 withthe slope of pprox 0.6+-0.1 and scatter of 0.1 dex. This indicates thatefficiency with which baryons are converted into stars decreases withincreasing cluster mass. We show that for a fixed choice of the initial massfunction (IMF) total stellar fraction in clusters is only a factor of ~3-5lower than the peak stellar fraction reached in Mpprox 10^12 Msun halos, andonly a factor of ~1.5-3 if the IMF becomes progressively more bottom heavy withincreasing mass in early type galaxies, as indicated by recent observations.The larger normalization and slope of the M*-M relation derived in this studyshows that the overall efficiency of star formation in massive halos issuppressed much less than was thought before and that feedback and associatedsuppression of star formation in massive halos should be weaker than assumed inmost of the current semi-analytic models and simulations.