Planck 2013 results. XI. All-sky model of thermal dust emission

TL;DR

The paper delivers an all-sky Planck+IRAS dust emission model at 5′ resolution by fitting a single modified blackbody per line of sight across 353–3000 GHz, producing maps of $\tau_{353}$, $T_{\rm obs}$, $β_{\rm obs}$, dust radiance $\mathcal{R}$, and $E(B-V)_{\rm xgal}$. It introduces a two-step fitting approach to mitigate CIB and noise-induced degeneracies, revealing a robust $β_{\rm obs}$–$T_{\rm obs}$ anticorrelation and notable opacity changes from diffuse to dense ISM, as well as a WIM-related excess at low $N_{\rm H}$. The study demonstrates that $\mathcal{R}$ is a more stable tracer of dust column density at high Galactic latitudes than $τ_{353}$, while $τ_{353}$ remains informative in molecular clouds when corrected for opacity variations; it also provides extinction calibrations based on SDSS quasars, yielding $E(B-V)_{\rm xgal}$ with strong correspondence to traditional maps but with improved high-latitude performance. Comparisons with the FDS dust model and the SFD extinction map illustrate Planck’s tighter spectral representation, revealing both global agreement and regional deviations tied to dust evolution and ISRF variations. The resulting Planck dust products enable more accurate foreground modeling for CMB analyses and offer improved tools for extragalactic reddening corrections, while highlighting the need to account for environmental dependence in dust properties.

Abstract

This paper presents an all-sky model of dust emission from the Planck 857, 545 and 353 GHz, and IRAS 100 micron data. Using a modified black-body fit to the data we present all-sky maps of the dust optical depth, temperature, and spectral index over the 353-3000 GHz range. This model is a tight representation of the data at 5 arc min. It shows variations of the order of 30 % compared with the widely-used model of Finkbeiner, Davis, and Schlegel. The Planck data allow us to estimate the dust temperature uniformly over the whole sky, providing an improved estimate of the dust optical depth compared to previous all-sky dust model, especially in high-contrast molecular regions. An increase of the dust opacity at 353 GHz, tau_353/N_H, from the diffuse to the denser interstellar medium (ISM) is reported. It is associated with a decrease in the observed dust temperature, T_obs, that could be due at least in part to the increased dust opacity. We also report an excess of dust emission at HI column densities lower than 10^20 cm^-2 that could be the signature of dust in the warm ionized medium. In the diffuse ISM at high Galactic latitude, we report an anti-correlation between tau_353/N_H and T_obs while the dust specific luminosity, i.e., the total dust emission integrated over frequency (the radiance) per hydrogen atom, stays about constant. The implication is that in the diffuse high-latitude ISM tau_353 is not as reliable a tracer of dust column density as we conclude it is in molecular clouds where the correlation of tau_353 with dust extinction estimated using colour excess measurements on stars is strong. To estimate Galactic E(B-V) in extragalactic fields at high latitude we develop a new method based on the thermal dust radiance, instead of the dust optical depth, calibrated to E(B-V) using reddening measurements of quasars deduced from Sloan Digital Sky Survey data.

Figures (30)

• Figure 1: All-sky Mollweide projections of Hi maps used in the determination of the offsets. The centre of the map is toward the Galactic centre. Left:Hi column density of low velocity clouds (LVC). Right: intermediate velocity clouds (IVC). See text.
• Figure 2: Polar orthographic projections of the LVC map (upper) and the IVC map (lower) shown in Fig. \ref{['fig:hi_maskhi']}. The left (right) panel is centred on the north (south) Galactic pole. Longitude increases clockwise (anticlockwise), with the two panels joining at $l=0$∘$^\circ$ and $b = 0$∘$^\circ$. Dotted lines representing constant longitude and latitude are spaced by 30∘$^\circ$. The radius from the pole is $\propto \cos(b)$, so this projection emphasizes features at high latitude.
• Figure 3: Masks used to estimate the zero levels of the maps. Left: "low $N_\ion{H}{i}$ mask" including pixels of the sky where the LVC column density is $<2\times10^{20}$cm$^{-2}$ and the IVC column density is below $<0.1\times10^{20}$cm$^{-2}$. Right: mask where the total Hi column density (LVC plus IVC) is lower than $3\times10^{20}$cm$^{-2}$.
• Figure 4: Polar orthographic projection of the low $N_\ion{H}{i}$ mask shown in Fig. \ref{['fig:hi_mask']} (left).
• Figure 5: Correlation plots used to estimate the Galactic zero levels of the IRAS and Planck maps (ZE subtracted). Left: Correlation of 857 and 3000GHz vs. Hi column density obtained on the $N_\ion{H}{i}<2\times10^{20}$cm$^{-2}$ mask (Fig. \ref{['fig:hi_mask']} bottom left). Right: Correlation of 353 and 545GHz vs. 857GHz obtained on the $N_\ion{H}{i} <3\times10^{20}$cm$^{-2}$ mask (Fig. \ref{['fig:hi_mask']} bottom right). All maps in the analysis were smoothed to a common resolution of 1∘$^\circ$. The black circles and the associated bars are the average and standard deviation of $I_\nu$ in bins of $N_\ion{H}{i}$ (left) and $I_{857}$ (right).