We present the new constraints on the cosmic optical background ( COB ) obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter ( IPP ) data .
After careful examination of data quality , the usable measurements free from the zodiacal light are integrated into sky maps at the blue ( \sim 0.44 \mu m ) and red ( \sim 0.64 \mu m ) bands .
Accurate starlight subtraction is achieved by referring to all-sky star catalogs and a Galactic stellar population synthesis model down to 32.0 mag .
We find that the residual light is separated into two components : one component shows a clear correlation with thermal 100 \mu m brightness , while another betrays a constant level in the lowest 100 \mu m brightness region .
Presence of the second component is significant after all the uncertainties and possible residual light in the Galaxy are taken into account , thus it most likely has the extragalactic origin ( i.e. , the COB ) .
The derived COB brightness is ( 1.8 \pm 0.9 ) \times 10 ^ { -9 } and ( 1.2 \pm 0.9 ) \times 10 ^ { -9 } erg s ^ { -1 } cm ^ { -2 } sr ^ { -1 } Å ^ { -1 } at the blue and red band , respectively , or 7.9 \pm 4.0 and 7.7 \pm 5.8 nW m ^ { -2 } sr ^ { -1 } .
Based on a comparison with the integrated brightness of galaxies , we conclude that the bulk of the COB is comprised of normal galaxies which have already been resolved by the current deepest observations .
There seems to be little room for contributions of other populations including ” first stars ” at these wavelengths .
On the other hand , the first component of the IPP residual light represents the diffuse Galactic light ( DGL ) —scattered starlight by the interstellar dust .
We derive the mean DGL-to-100 \mu m brightness ratios of 2.1 \times 10 ^ { -3 } and 4.6 \times 10 ^ { -3 } at the two bands , which are roughly consistent with the previous observations toward denser dust regions .
Extended red emission in the diffuse interstellar medium is also confirmed .