Extremely red objects in the UKIDSS Uultra Deep Survey Early Data Release C. Simpson O. Almaini M. Cirasuolo J. Dunlop S. Foucaud P. Hirst R. Ivison M. Page S. Rawlings K. Sekiguchi I. Smail Michael G. Watson 2381/11041 https://figshare.le.ac.uk/articles/journal_contribution/Extremely_red_objects_in_the_UKIDSS_Uultra_Deep_Survey_Early_Data_Release/10106243 We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM–Newton Deep Field. We find a total of 3715 objects over 2013 arcmin2 with R−K > 5.3 and K≤ 20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that active galactic nuclei are more prevalent among the passive ERO population. 2012-10-01 15:05:05 surveys;galaxies evolution;galaxies starbust;infrared galaxies