The Properties of Lyα Nebulae: Gas Kinematics from Nonresonant Lines

With the Very Large Telescope/X-shooter, we obtain optical and near-infrared spectra of six Lyα blobs at z ~ 2.3. For a total sample of eight Lyα blobs (including two that we have previously studied), the majority (6/8) have broadened Lyα profiles with shapes ranging from a single peak to symmetric or asymmetric double-peaked. The remaining two systems, in which the Lyα profile is not significantly broader than the [O III] or Hα emission lines, have the most spatially compact Lyα emission, the smallest offset between the Lyα and the [O III] or Hα line velocities, and the only detected C IV and He II lines in the sample, implying that a hard ionizing source, possibly an active galactic nucleus (AGN), is responsible for their lower optical depth. Using three measures—the velocity offset between the Lyα line and the nonresonant [O III] or Hα line (Δv Lyα), the offset of stacked interstellar metal absorption lines, and a new indicator, the spectrally resolved [O III] line profile—we study the kinematics of gas along the line of sight to galaxies within each blob center. These three indicators generally agree in velocity and direction and are consistent with a simple picture in which the gas is stationary or slowly outflowing at a few hundred km s-1 from the embedded galaxies. The absence of stronger outflows is not a projection effect: the covering fraction for our sample is limited to