  We present the results of a Spitzer IRAC and MIPS 24 micron study of extended
Lyman-alpha clouds (or Lyman-alpha Blobs, LABs) within the SSA22 filamentary
structure at z = 3.09. We detect 6/26 LABs in all IRAC filters, four of which
are also detected at 24 micron, and find good correspondence with the 850
micron measurements of Geach et al. 2005. An analysis of the rest-frame
ultraviolet, optical, near- and mid-infrared colors reveals that these six
systems exhibit signs of nuclear activity (AGN)and/or extreme star formation.
Notably, they have properties that bridge galaxies dominated by star formation
(Lyman-break galaxies; LBGs) and those with AGNs (LBGs classified as QSOs). The
LAB systems not detected in all four IRAC bands, on the other hand, are, as a
group, consistent with pure star forming systems, similar to the majority of
the LBGs within the filament. These results indicate that the galaxies within
LABs do not comprise a homogeneous population, though they are also consistent
with scenarios in which the gas halos are ionized through a common mechanism
such as galaxy-scale winds driven by the galaxies within them, or gravitational
heating of the collapsing cloud itself.

Astrophysics