First detection of the WIM dust emission. Implication for the Cosmic Far-Infrared Background

TL;DR

This study detects dust emission from the Warm Ionised Medium (WIM) at high Galactic latitudes, revealing its spectral properties and implications for the Cosmic Far-Infrared Background, using COBE and HI data analysis.

Contribution

First detection of WIM dust emission at high Galactic latitude, with detailed spectral characterization and implications for the CFIRB.

Findings

WIM dust emission detected at 10 sigma in the 200-350 micron band.

WIM dust has a temperature of 29.1 K with a specific emissivity law.

Detection reduces the estimated intensity of the CFIRB around 200 microns.

Abstract

We present a new analysis of the far-IR emission at high Galactic latitude based on COBE and HI data. A decomposition of the Far-IR emission over the HI, H^+ and H_2 Galactic gas components and the Cosmic Far InfraRed Background (CFIRB) is described. For the first time the far-IR emission of dust associated with the Warm Ionised Medium (WIM) is evidenced. This component determined on about 25% of the sky is detected at a 10 sigma level in the [200, 350]micron band. The best representation of the WIM dust spectrum is obtained for a temperature of 29.1 K and an emissivity law $tau/N_H+=3.8 \pm 0.8 10^{-26} (\lambda/250\mic)^{-1} cm^2$. With a spectral index equal to 2, the emissivity law becomes $\tau/N_H^+= 1.0 \pm 0.2 10^{-25} (\lambda/250\mic)^{-2} cm^2$, with a temperature of 20 K, which is significantly higher than the temperature of dust associated with HI gas. The variation in the dust spectrum from the HI to the WIM component can be explained by only changing the upper cutoff of the Big Grain size distribution from 0.1 micron to 30 nm. The detection of IR emission of dust in the WIM significantly decreases the intensity of the CFIRB, especially around 200 micron which corresponds to the peak of energy.