Bulgeless Galaxies at Intermediate Redshift: Sample Selection, Colour
  Properties, and the Existence of Powerful AGN
  We present a catalogue of bulgeless galaxies, which includes 19225 objects
selected in four of the deepest, largest multi-wavelength datasets available --
COSMOS, AEGIS, GEMS and GOODS -- at intermediate redshift ($0.4 \leq z \leq
1.0$). The morphological classification was provided by the Advanced Camera for
Surveys General Catalogue (ACS-GC), which used publicly available data obtained
with the ACS instrument on the Hubble Space Telescope. Rest-frame photometric
quantities were derived using kcorrect. We analyse the properties of the sample
and the evolution of pure-disc systems with redshift. Very massive [$\log
(M_\star/M_{\odot}) > 10.5$] bulgeless galaxies contribute to ~30% of the total
galaxy population number density at $z \geq 0.7$, but their number density
drops substantially with decreasing redshift. We show that only a negligible
fraction of pure discs appear to be quiescent systems, and red sequence
bulgeless galaxies show indications of dust-obscured star formation. X-ray
catalogues were used to search for X-ray emission within our sample. After
visual inspection and detailed parametric morphological fitting we identify 30
AGN that reside in galaxies without a classical bulge. The finding of such
peculiar objects at intermediate redshift shows that while AGN growth in
merger-free systems is a rare event (0.2% AGN hosts in this sample of bulgeless
galaxies), it can indeed happen relatively early in the Universe history.
