The extent of black hole growth during different galaxy evolution phases and
the connection between galaxy compactness and AGN activity remain poorly
understood. We use Hubble Space Telescope imaging of the CANDELS fields to
identify star-forming and quiescent galaxies at z=0.5-3 in both compact and
extended phases and use Chandra X-ray imaging to measure the distribution of
AGN accretion rates and track black hole growth within these galaxies.
Accounting for the impact of AGN light changes ~20% of the X-ray sources from
compact to extended galaxy classifications. We find that ~10-25% of compact
star-forming galaxies host an AGN, a mild enhancement (by a factor ~2) compared
to extended star-forming galaxies or compact quiescent galaxies of equivalent
stellar mass and redshift. However, AGN are not ubiquitous in compact
star-forming galaxies and this is not the evolutionary phase, given its
relatively short timescale, where the bulk of black hole mass growth takes
place. Conversely, we measure the highest AGN fractions (~10-30%) within the
relatively rare population of extended quiescent galaxies. For massive galaxies
that quench at early cosmic epochs, substantial black hole growth in this
extended phase is crucial to produce the elevated black hole mass-to-galaxy
stellar mass scaling relation observed for quiescent galaxies at z~0. We also
show that AGN fraction increases with compactness in star-forming galaxies and
decreases in quiescent galaxies within both the compact and extended
sub-populations, demonstrating that AGN activity depends closely on the
structural properties of galaxies.Comment: 29 pages, 18 figures, submitted to MNRAS. Primary results are shown
in Fig 7 and summarised by Fig 12. See Fig 16 and 17 for key
interpretation/conclusion
