GAS KINEMATICS IN Ly alpha NEBULAE

Exploring the origin of Ly alpha nebulae ("blobs") at high redshift requires measurements of their gas kinematics that are impossible with only the resonant, optically thick Ly alpha line. To define gas motions relative to the systemic velocity of the blob, the Ly alpha line must be compared with an optically thin line like H alpha lambda 6563, which is not much altered by radiative transfer effects and is more concentrated about the galaxies embedded in the nebula's core. We obtain optical and near-IR (NIR) spectra of the two brightest Ly alpha blobs (CDFS-LAB01 and CDFS-LAB02) from the Yang et al. sample using the Magellan/Magellan Echellette Spectrograph optical and Very Large Telescope/SINFONI NIR spectrographs. Both the Ly alpha and H alpha lines confirm that these blobs lie at the survey redshift, z similar to 2.3. Within each blob, we detect several H alpha sources, which roughly correspond to galaxies seen in Hubble Space Telescope rest-frame UV images. The H alpha detections show that these galaxies have large internal velocity dispersions (sigma(upsilon) = 130-190 km s(-1)) and that, in the one system (LAB01), where we can reliably extract profiles for two H alpha sources, their velocity difference is Delta upsilon similar to 440 km s(-1). 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 Ly alpha blobs inhabit massive dark matter halos that will evolve into those typical of present-day rich clusters and that the embedded galaxies may eventually become brightest cluster galaxies. To determine whether the gas near the embedded galaxies is predominantly infalling or outflowing, we compare the Ly alpha and H alpha line centers, finding that Ly alpha is not offset (Delta upsilon(Ly alpha) = +0 km s(-1)) in LAB01 and redshifted by only +230 km s(-1) in LAB02. These offsets are small compared to those of Lyman break galaxies, which average +450 km s(-1) and extend to about +700 km s(-1). In LAB02, we detect C II lambda 1334 and Si II lambda 1526 absorption lines, whose blueward shifts of similar to 200 km s(-1) are consistent with the small outflow implied by the redward shift of Ly alpha. We test and rule out the simplest infall models and those outflow models with super/hyperwinds, which require large outflow velocities. Because of the unknown geometry of the gas distribution and the possibility of multiple sources of Ly alpha 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.