Submillimeter observations of the J2142-4423 Ly

Aims. We present observations aimed at exploring both the nature of Lyα emitting nebulae (“Lyα 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 $z=2.38$. Methods. 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 $10\arcmin \times 10\arcmin$ map at 870 ${\mu {\rm m}}$, and we performed multiple checks of the quality of data processing and source extraction. Results. 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 ${\mu {\rm m}}$ flux densities in the range 3–21 mJy, rms noise ~0.8–2.4 mJy, and far-IR luminosities probably in the range ${\sim}$5–$20\times 10^{12}$ $L_\odot$. Only one of the four 50 kpc-extended Lyα blobs has a secure 870 ${\mu {\rm m}}$ counterpart. The 870 ${\mu {\rm m}}$ 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 ${\mu {\rm m}}$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