  We present observations aimed at exploring both the nature of Lya emitting
nebulae (Lya blobs) at z=2.38 and the way they trace large scale structure
(LSS), by exploring their proximity to maximum starbursts through submillimeter
emission. Our most important objectives are to make a census of associated
submillimeter galaxies (SMGs), check their properties, and look for a possible
overdensity in the protocluster J2142-4426 at z=2.38.
  We used the newly commissioned Large APEX Bolometer Camera (LABoCa) on the
Atacama Pathfinder EXperiment (APEX) telescope, in its Science Verification
phase, to carry out a deep 10'x10' map at 870 micron, and we performed multiple
checks of the quality of data processing and source extraction.
  Our map, the first published deep image, confirms the capabilities of
APEX/LABoCa as the most efficient current equipment for wide and deep submm
mapping. Twenty-two sources were securely extracted with 870 micron flux
densities in the range 3-21 mJy, rms noise 0.8-2.4 mJy, and far-IR luminosities
probably in the range ~5-20 x 10(12) Lo. Only one of the four 50 kpc-extended
Lya blobs has a secure 870 micron counterpart. The 870 micron source counts in
the whole area are marginally higher than in the SHADES SCUBA survey, with a
possible over-density around this blob. The majority of the 3.6-24 micron SEDs
of the submillimeter sources indicate they are starburst dominated, with
redshifts mostly >2. However, there is evidence of a high-z AGN in ~30% of the
sources.
