The stellar mass function of the most-massive galaxies at 3 <z <5 in the UKIDSS Ultra Deep Survey

We have analysed a sample of 1292 4.5-mu m-selected galaxies at z &gt;= 3, over 0.6 deg2 of the UKIRT Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS). Using photometry from the U band through 4.5 mu m, we have obtained photometric redshifts and derived stellar masses for our sources. Only two of our galaxies potentially lie at z &gt; 5. We have studied the galaxy stellar mass function at 3 10 between z = 5 and 3, indicating that the assembly rate of these galaxies proceeded &gt; 20 times faster at these redshifts than at 0