Abstract:
Understanding how super-massive black holes (SMBHs) form and grow in the early universe has become a major challenge since the discovery of luminous quasars only 700 million years after the Big Bang. Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust. Although the last phase has been identified out to redshift z=7.6, a transitioning quasar has not been found at similar redshifts due to their faintness at optical and near-infrared wavelengths. In this seminar, I will present our recent discovery of an ultraviolet (UV) compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of z = 7.1899 +/- 0.0005 in GOODS-North. The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 pc. A red point source in the far-UV is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, indicating the emergence of a uniquely UV-compact star-forming region or a Compton-thick super-Eddington black hole accretion disk at the dusty starburst core. In the latter case, the observed properties are consistent with predictions from cosmological simulations and suggest GNz7q is an antecedent to unobscured luminous quasars at later epochs. I will also discuss the potential high abundance of high-redshift dusty-obscured quasars that have been missed in previous surveys and their contributions to the cosmic star-formation rate density at z>6.
