ALMA confirmation of an obscured hyperluminous radio-loud AGN at z=6.853 associated with a dusty starburst in the 1.5 deg2 COSMOS field

We present band 6 ALMA observations of a heavily-obscured radio-loud (L-1.4 GHz=10(25.4) W Hz(-1)) AGN candidate at zphot=6.83 +/- 0.06 found in the 1.5 deg(2) COSMOS field. The ALMA data reveal detections of exceptionally strong [CII]158 mu m (z[CII]=6.8532) and underlying dust continuum emission from this object (COS-87259), where the [CII] line luminosity, line width, and 158 mu m continuum luminosity are comparable to that seen from z similar to 7 sub-mm galaxies and quasar hosts. The 158 mu m continuum detection suggests a total infrared luminosity of 9x10(12) L-? with corresponding very large obscured star formation rate (1300 M-?/yr) and dust mass (2x10(9) M-?). The strong break seen between the VIRCam and IRAC photometry perhaps suggests that COS-87259 is an extremely massive reionization era galaxy with M-*approximate to 1.7x10(11) M-?. Moreover, the MIPS, PACS, and SPIRE detections imply that this object harbors an AGN that is heavily obscured (tau 9.7 mu m=2.3) with a bolometric luminosity of approximately 5x10(13) L?. Such a very high AGN luminosity suggests this object is powered by an approximate to 1.6 x 10(9) M-? black hole if accreting near the Eddington limit, and is effectively a highly-obscured version of an extremely UV-luminous (M-1450 approximate to-27.3) z similar to 7 quasar. Notably, these z similar to 7 quasars are an exceedingly rare population (similar to 0.001 deg(-2)) while COS-87259 was identified over a relatively small field. Future very wide-area surveys with, e.g., Roman and Euclid have the potential to identify many more extremely red yet UV-bright z?7 objects similar to COS-87259, providing richer insight into the occurrence of intense obscured star formation and supermassive black hole growth among this population.