ChandraDetections of SCUBA Galaxies around High‐zRadio Sources

The most massive galaxies in the present day universe are the giantellipticals found in the centers of rich clusters. These have old, coevalstellar populations, suggesting they formed at high redshift, and are expectedto host supermassive black holes (SMBHs). The recent detection of severalhigh-redshift radio galaxies (HzRGs) at submm wavelengths confirms that indeedsome massive galaxies may have formed the bulk of their stellar populations inspectacular dust-enshrouded starbursts at high-z. In this letter we comparesensitive Chandra X-ray images - which identify actively-fueled SMBHs - andsubmm observations - capable of detecting obscured activity in luminousgalaxies at high redshift - of the environments of three HzRGs. Theseobservations exhibit overdensities of X-ray sources in all 3 fields and a closecorrespondence between the Chandra and SCUBA populations. This suggests thatboth substantial star formation and nuclear activity may be occuring in theseregions. We identify possible pairs of Chandra sources with each of 2 SCUBAsources, suggesting that their ultraluminous activity may be triggered by theinteraction of two massive galaxies, each of which hosts an accreting SMBH. Thepresence of two SMBHs in the resulting remanent is predicted to produce aflattened stellar core in the galaxy, a morphological signature frequently seenin luminous cluster ellipticals. Hence the confirmation of pairs of Chandrasources within individual, luminous SCUBA galaxies would provide additionalevidence that these galaxies at z~2-4 are the progenitors of the giantelliptical galaxies found in clusters at the present-day.Comment: 5 pages, submitted to ApJ, revised in response to referee's repor