Pinpointing the Molecular Gas within a Lyman Alpha Blob at z ~ 2.7
  We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions
from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics,
determine the location of the dominant energy source, and study the physical
conditions of the molecular gas. CO line and dust continuum emission are
detected at the location of a strong MIPS source that is offset by ~1.5" from
the Ly-alpha peak. Neither of these emission components is resolved with the
1.7" beam, showing that the gas and dust are confined to within ~7kpc from this
galaxy. No millimeter source is found at the location of the Ly-alpha peak,
ruling out a central compact source of star formation as the power source for
the Ly-alpha emission. Combined with a spatially-resolved spectrum of Ly-alpha
and HeII, we constrain the kinematics of the extended gas using the CO emission
as a tracer of the systemic redshift. Near the MIPS source, the Ly-alpha
profile is symmetric and its line center agrees with that of CO line, implying
that there are no significant bulk flows and that the photo-ionization from the
MIPS source might be the dominant source of the Ly-alpha emission. In the
region near the Ly-alpha peak, the gas is slowly receding (~100km/s) with
respect to the MIPS source, thus making the hyper-/superwind hypothesis
unlikely. We find a sub-thermal line ratio between two CO transitions,
I_CO(5-4)/I_CO(3-2)=0.97+/-0.21. This line ratio is lower than the average
values found in high-z SMGs and QSOs, but consistent with the value found in
the Galactic center, suggesting that there is a large reservoir of low-density
molecular gas that is spread over the MIPS source and its vicinity.
