We present band 6 ALMA observations of a heavily-obscured radio-loud
(L1.4Β GHzβ=1025.4 W Hzβ1) AGN candidate at
zphotβ=6.83Β±0.06 found in the 1.5 deg2 COSMOS field. The ALMA
data reveal detections of exceptionally strong [CII]158ΞΌm
(z[CII]β=6.8532) and underlying dust continuum emission from this
object (COS-87259), where the [CII] line luminosity, line width, and 158ΞΌm
continuum luminosity are comparable to that seen from zβΌ7 sub-mm galaxies
and quasar hosts. The 158ΞΌm continuum detection suggests a total infrared
luminosity of 9Γ1012Lββ with corresponding very large obscured
star formation rate (1300 Mββ/yr) and dust mass (2Γ109Mββ). The strong break seen between the VIRCam and IRAC photometry
perhaps suggests that COS-87259 is an extremely massive reionization era galaxy
with Mβββ1.7Γ1011Mββ. Moreover, the MIPS, PACS, and
SPIRE detections imply that this object harbors an AGN that is heavily obscured
(Ο9.7ΞΌmββ=2.3) with a bolometric luminosity of
approximately 5Γ1013Lββ. Such a very high AGN luminosity
suggests this object is powered by an β1.6 Γ 109Mββ
black hole if accreting near the Eddington limit, and is effectively a
highly-obscured version of an extremely UV-luminous (M1450βββ27.3)
zβΌ7 quasar. Notably, these zβΌ7 quasars are an exceedingly rare
population (βΌ0.001 degβ2) 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
zβ³7 objects similar to COS-87259, providing richer insight into the
occurrence of intense obscured star formation and supermassive black hole
growth among this population.Comment: 12 pages, 7 figures, 1 table. Updated to accepted version (MNRAS