Rogier Windhorst

Title: Observing supermassive black-hole growth with HST and JWST: When during galaxy assembly did AGN growth take place?

Abstract: Accretion disks around Supermassive Black-Holes (SMBH's) in the centers of
galaxies cause Active Galactic Nuclei (AGN), which are observable over the entire
electromagnetic spectrum and out to the beginning of galaxy formation. The
gradual assembly of galaxies is believed to have resulted in SMBH's today. The
growth of SMBH's is largely hidden by dust, and possibly by large time delays
between galaxy mergers and the feeding of the central monster, so that the
connection between galaxy assembly and SMBH-growth is at best circumstantial. 

Even the current deepest radio and X-ray surveys are not deep enough to trace
SMBH-growth via weak AGN in faint galaxies over cosmic time. In this talk, we
therefore focus on how to best investigate to what extent the process of
hierarchical galaxy assembly and SMBH-growth has gone hand-in-hand --- and with
what kind of time delay. Facilities like HST WFC3 and JWST are needed to trace
this process from the epoch of reionization to the present. Using panchromatic
deep Hubble WFC3 imaging data, ACS and WFC3 grism spectra, and ground-based
spectroscopy in GOODS and the HUDF, we address this issue through the epoch
dependent rate of major mergers in massive galaxies in the HUDF, and through
SED-fitting of objects with and without (known) AGN in GOODS. 

On average, the field galaxy population at z=1--3 has an underlying star-forming
SED with typical ages of 0.1--1 Gyr and stellar masses between 10^8 and 10^12 Mo.
Most AGN-dominated objects at z=0.5--2, however, have stellar masses >10^10 Mo
and an underlying stellar SED age that is older than >~1 Gyr on average. This
suggests that AGN growth/SMBH-feeding may become visible about >~1 Gyr AFTER
the dynamical event which triggered the dominant starburst at these redshifts.
This may also be reflected in the peak in the massive galaxy major merger-rate,
compared to the peak in the redshift distribution of weak AGN. Hence, SMBH growth
likely kept in pace with galaxy assembly, but with a time-delay of at least 1 Gyr
since the last merger or starburst, as recent hierarchical models predicted.

Throughout this talk, we discuss how the James Webb Space Telescope will expand
on this topic in this decade from the epoch of First Light to the present