The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at
  z=3
  We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift.
