Hot Gas, Cold Gas and Sub-Halos in a Lyman-alpha Blob at Redshift 2.38
  We present integral field spectroscopy of a Lyman-alpha blob at redshift
2.38, with a spectral resolution three times better than previous published
work. As with previous observations, the blob has a chaotic velocity structure,
much of which breaks up into multiple components. Our spectroscopy shows,
however, that some of these multiple components are extremely narrow: they have
velocity widths of less than 100 km/s.
  Combining these new data with previous observations, we argue that this
Lyman-alpha blob resides in a dark-matter halo of around 10^13 solar masses. At
the centre of this halo are two compact red massive galaxies. They are
surrounded by hot gas, probably a super-wind from merger-induced nuclear
starbursts. This hot gas has shut down star formation in the non-nuclear region
of these galaxies, leading to their red-and-dead colours.
  A filament or lump of infalling cold gas is colliding with the hot gas phase
and being shocked to high temperatures, while still around 30kpc from the red
galaxies. The shock region is self-absorbed in Lyman-alpha but produces C IV
emission.
  Further out still, the cold gas in a number of sub-halos is being lit up,
most likely by a combination of tidally triggered star formation, bow-shocks as
they plough through the hot halo medium, resonant scattering of Lyman-alpha
from the filament collision, and tidal stripping of gas which enhances the
Lyman-alpha escape fraction. The observed Lyman-alpha emission from the Blob is
dominated by the sum of the emission from these sub-halos.
  On statistical grounds, we argue that Lyman-alpha blobs are not greatly
elongated in shape, and that most are not powered by ionisation or scattering
from a central active galactic nucleus or starburst.
