"So far, many supermassive black holes with >1e9 Msun have been discovered at z > 6 as quasars. Mm/submm observations revealed that their host galaxies are experiencing vigorous star formation (>100-1000 Msun/yr), supported by huge amounts of cold molecular gas (~1e10 Msun) and dust (~1e8 Msun). However, as previous quasar surveys targeted luminous/massive-end objects at z > 6, the above views could be strongly biased ones on galaxy evolution.
The z > 6 quasars uncovered with the Subaru Hyper Suprime-Cam (HSC) are indeed much (~2-4 mag) fainter than the luminous-end objects (Matsuoka et al. 2016), which can serve to remove any potential bias drastically. We then conducted ALMA follow-up observations to characterize star forming nature of their hosts. As a result, we found that they are not so luminous at both [CII] and FIR continuum (indeed, they are classified as “LIRGs”): the inferred star formation rate is only ~40 Msun/yr. As our quasars constitute the “knee” of the luminosity function at z ~ 6, the LIRG-like nature we found would be characteristic to bulk of the quasar-host galaxies at that epoch. These information could be the new reference for galaxy evolution models. "