Chandra Detections of SCUBA Galaxies around High-z Radio Sources

Abstract

The most massive galaxies in the present day universe are the giant ellipticals found in the centers of rich clusters. These have old, coeval stellar populations, suggesting they formed at high redshift, and are expected to host supermassive black holes (SMBHs). The recent detection of several high-redshift radio galaxies (HzRGs) at submm wavelengths confirms that indeed some massive galaxies may have formed the bulk of their stellar populations in spectacular dust-enshrouded starbursts at high-z. In this letter we compare sensitive Chandra X-ray images - which identify actively-fueled SMBHs - and submm observations - capable of detecting obscured activity in luminous galaxies at high redshift - of the environments of three HzRGs. These observations exhibit overdensities of X-ray sources in all 3 fields and a close correspondence between the Chandra and SCUBA populations. This suggests that both substantial star formation and nuclear activity may be occuring in these regions. We identify possible pairs of Chandra sources with each of 2 SCUBA sources, suggesting that their ultraluminous activity may be triggered by the interaction of two massive galaxies, each of which hosts an accreting SMBH. The presence of two SMBHs in the resulting remanent is predicted to produce a flattened stellar core in the galaxy, a morphological signature frequently seen in luminous cluster ellipticals. Hence the confirmation of pairs of Chandra sources within individual, luminous SCUBA galaxies would provide additional evidence that these galaxies at z~2-4 are the progenitors of the giant elliptical galaxies found in clusters at the present-day.