Kinematics of Gas in Lyman Alpha Nebulae
  Exploring the origin of Ly-alpha nebulae (blobs) requires measurements of
their gas kinematics that are impossible with only the resonant,
optically-thick LyA line. To define gas motions relative to the systemic
velocity of the blob, the LyA line must be compared with an optically-thin line
like Halpha, which is not much altered by radiative transfer effects. We obtain
optical and NIR spectra of the two brightest LyA blobs from Yang et al. sample
using the Magellan/MagE and VLT/SINFONI. Both the LyA and Halpha lines confirm
that these blobs lie at the survey redshift, z~2.3. Within each blob, we detect
several Halpha sources, which roughly correspond to galaxies seen in HST
images. The Halpha detections show that these galaxies have large internal
velocity dispersions (130 - 190km/s) and that, in the one system (LAB01), their
velocity difference is ~440 km/s. The presence of multiple galaxies within the
blobs, and those galaxies' large velocity dispersions and large relative
motion, is consistent with our previous finding that LyA blobs inhabit massive
dark matter halos that will evolve into those typical of rich clusters today.
To determine whether the gas near the embedded galaxies is predominantly
infalling or outflowing, we compare the LyA and Halpha line centers, finding
that LyA is not offset (Delta LyA = +0km/s) in LAB01 and redshifted by only
+230 km/s in LAB02. These offsets are small compared to those of Lyman break
galaxies, which average +450 km/s and extend to about +700 km/s. We test and
rule out the simplest infall models and those outflow models with
super/hyper-winds, which require large outflow velocities. Because of the
unknown geometry of the gas distribution and the possibility of multiple
sources of LyA emission embedded in the blobs, a larger sample and more
sophisticated models are required to test more complex or a wider range of
infall and outflow scenarios.
