The properties of Lyα nebulae: Gas kinematics from nonresonant lines

Yujin Yang, Ann Zabludoff, Knud Jahnke, Romeel Davé

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31 Scopus citations


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-1from the embedded galaxies. The absence of stronger outflows is not a projection effect: the covering fraction for our sample is limited to <1/8 (13%). The outflow velocities exclude models in which star formation or AGNs produce "super-" or "hyper"winds of up to ∼1000 km s-1. The Δv Lyαoffsets here are smaller than typical of Lyman break galaxies but similar to those of compact Lyα emitters (LAEs). The latter suggests a connection between blob galaxies and LAEs and that outflow speed cannot be a dominant factor in driving extended Lyα emission. For one Lyα blob (CDFS-LAB14), whose Lyα profile and metal absorption line offsets suggest no significant bulk motion, we use a simple radiative transfer model to make the first column density measurement of gas in an embedded galaxy, finding it consistent with a damped Lyα absorption system. Overall, the absence of clear inflow signatures suggests that the channeling of gravitational cooling radiation into Lyα is not significant over the radii probed here. However, one peculiar system (CDFS-LAB10) has a blueshifted Lyα component that is not obviously associated with any galaxy, suggesting either displaced gas arising from tidal interactions among blob galaxies or gas flowing into the blob center. The former is expected in these overdense regions where Hubble Space Telescope images resolve many galaxies. The latter might signify the predicted but elusive cold gas accretion along filaments.

Original languageEnglish (US)
Article number114
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 1 2014


  • galaxies: formation
  • galaxies: high-redshift
  • intergalactic medium

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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