First Systematic Search for Oxygen-Line Blobs at High Redshift:
  Uncovering AGN Feedback and Star-Formation Quenching
  We present the first systematic search for extended metal-line
[OII]{\lambda}{\lambda}3726,3729 nebulae, or [OII] blobs (OIIBs), at z=1.2
using deep narrowband imaging with a survey volume of 1.9x10^5 Mpc^3 on the
0.62 deg^2 sky of Subaru-XMM Deep Survey (SXDS) field. We discover a giant
OIIB, dubbed 'OIIB 1', with a spatial extent over ~75 kpc at a spectroscopic
redshift of z=1.18, and also identify a total of twelve OIIBs with a size of
>30 kpc. Our optical spectrum of OIIB 1 presents [NeV]{\lambda}3426 line at the
6{\sigma} level, indicating that this object harbors an obscured type-2 AGN.
The presence of gas outflows in this object is suggested by two marginal
detections of FeII{\lambda}2587 absorption and FeII*{\lambda}2613 emission
lines both of which are blueshifted at as large as 500-600 km/s, indicating
that the heating source of OIIB 1 is AGN or associated shock excitation rather
than supernovae produced by starbursts. The number density of OIIB 1-type giant
blobs is estimated to be ~5x10^{-6} Mpc^{-3} at z~1.2, which is comparable with
that of AGNs driving outflow at a similar redshift, suggesting that giant OIIBs
are produced only by AGN activity. On the other hand, the number density of
small OIIBs, 6x10^{-5} Mpc^{-3}, compared to that of z~1 galaxies in the blue
cloud in the same M_B range, may imply that 3% of star-forming galaxies at z~1
are quenching star formation through outflows involving extended [OII]
emission.
