Determination of the Far-infrared Cosmic Background Using Cobe Dirbe and Wham Data

Determination of the cosmic infrared background (CIB) at far-infrared wavelengths using COBE DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Most previous determinations of the far-infrared CIB were based on the detection of residual isotropic emission in skymaps fromwhich the emission from interplanetary dust and the neutral interstellar mediumwere removed. In this paper we use the Wisconsin H Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose DIRBE far-infrared data for five high Galactic latitude regions into H iY and H -correlated components and a residual component. We find the H -correlated component to be consistent with zero for each region, yielding CIB results that are essentially the same as those previously derived by the COBE DIRBE team: I (nW m 2 sr ) < 75,<32, =25 8, and =13 3 at 60, 100, 140, and 240 m, respectively (upper limits are 2 ). For comparison, the estimated integrated light from galaxies based on Spitzer 160 m source counts is 13:7 1:7 and 10:7 1:4 nW m 2 sr 1 at 140 and 240 m, respectively.We derive upper limits on the 100 memissivity of the ionizedmedium that are typically about 40% of the 100 m emissivity of the neutral atomic medium. If H is not a reliable tracer of far-infrared emission, we show that our analysis would underestimate the emissivity of the ionized medium and could slightly overestimate the CIB. Subject headingg s: cosmology: observations — diffuse radiation — Galaxy: general — infrared: ISM — ISM: general Online material: color figure