Foreground: Reddening (E(B-V)) Map

Reddening (E(B-V)) Map (Lenz et al. 2017)

Lenz et al. (2017) derived a new map of interstellar reddening, covering the 39% of the sky with low HI column densities (N_HI < 4 × 10²⁰ cm⁻²) at 16.1 arcminute resolution, based on all-sky observations of Galactic HI emission by the HI4PI Survey. In this low column density regime, they derived a characteristic value of N_HI/E(B−V)=8.8×10²¹cm²mag⁻¹ for gas with |v_LSR|< 90 km s⁻¹ and found no significant reddening associated with gas at higher velocities. Their reddening map was derived by correlating HI emission integrated over |v_LSR|< 90 km s⁻¹ with the reddening map of Schlegel, Finkbeiner and Davis (1998, SFD). They compared their HI-based reddening map with the SFD reddening map and found them consistent to within a scatter of ≃5 mmag. Further, the differences between their map and the SFD map are in excellent agreement with the low resolution (4.5 degree) corrections to the SFD map derived by Peek and Graves (2010) based on observed reddening toward passive galaxies. They therefore argued that their HI-based map provides the most accurate interstellar reddening estimates in the low column density regime to date.

LAMBDA hosts HEALPix maps of E(B-V) and HI4PI HI column density for absolute velocities lower than 90 km/s, both of which were obtained from Harvard Dataverse.

The HI column density map is available and is described here.

A short notebook with examples on how to use the E(B-V) map is available from Daniel Lenz on github. This includes:

• Conversions from E(B-V) to extinction in a larger number of bandpasses, according to Schlafly & Finkbeiner (2011).
• A function to extract the E(B-V) value for a particular line of sight.

More details can be found in:

"A new, large-scale map of interstellar reddening derived from HI emission", Lenz, Hensley, and Doré 2017, ApJ, in press, arXiv

Harvard Dataverse

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