A rocket-borne observation of the far-infrared sky at high Galactic latitude

We have measured the surface brightness of the far-infrared sky at lambda = 134, 154, and 186 micrometers at high Galactic latitude using a liquid-He-cooled, rocket-borne telescope. The telescope scanned over a 5 deg x 20 deg region which includes infrared cirrus, high-latitude molecular clouds, the starburst galaxy M82, and the H I Hole in Ursa Major, a region with uniquely low H I column density. The measured brightness at 134, 154, and 186 micrometers is well correlated with the 100 micrometers brightness measured by IRAS and, in regions excluding molecular clouds, with H I column density. The spectrum of the component correlated with H I is well fitted by a gray-body spectrum with a temperature of 16.4 (+2.3/-1.8) K, assuming an emissivity proportional to lambda(exp -2). Assuming a constant far-infrared dust emissivity per hydrogen nucleus, the ratio of the H2 column density to the velocity-integrated CO intensity in the high-latitude molecular cloud is NH2/W(sub co) = (1.6 +/- 0.3) x 10(exp 20)/sq cm/(K km/s). The residual brightness after subtracting the emission correlated with H I column density is lambda I(sub lambda)(154 micrometers) = (1.4 +/- 0.6) x 10(exp -12) W/sq cm/sr, yielding an upper limit to the far-infrared extragalactic background radiation of lambda I(sub lambda)(154 micrometers) is less than 2.6 x 10(exp -12) W/sq cm/sr.