  Using the 2MASS 2nd Incremental Data Release and the Zodiacal-Subtracted
Mission Average maps of COBE/DIRBE, we estimate the cosmic background in the J
(1.25 micron) and K (2.2 microns) bands using selected areas representing 550
square degrees of sky. We find a J background of 22.9 \pm 7.0 kJy/sr (54.0 \pm
16.8 nW/m2/sr) and a K background of 20.4 \pm 4.9 kJy/sr (27.8 \pm 6.7
nW/m2/sr). This large scale study shows that the main uncertainty comes from
the residual zodiacal emission. The cosmic background we obtain is
significantly higher than integrated galaxy counts (3.6 \pm 0.8 kJy/sr and 5.3
\pm 1.2 kJy/sr for J and K, respectively), suggesting either an increase of the
galaxy luminosity function for magnitudes fainter than 30 or the existence of
another contribution to the cosmic background from primeval stars, black holes,
or relic particle decay.

Astrophysics