Lenz, Hensley & Doré (2017) – A New, Large-scale Map of Interstellar Reddening Derived from H I Emission

We present a new map of interstellar reddening, covering the 39% of the sky with low H I column densities ({N}{{H}{{I}}}< 4× {10}20 cm-2 or E(B-V)≈ 45 mmag) at 16\buildrel{ \prime}\over{.} 1 resolution, based on all-sky observations of Galactic H I emission by the HI4PI Survey. In this low-column-density regime, we derive a characteristic value of {N}{{H}{{I}}}/E(B-V)=8.8 × {10}21 {{cm}}2 {{mag}}-1 for gas with | {v}{LSR}| < 90 km s-1 and find no significant reddening associated with gas at higher velocities. We compare our H I-based reddening map with the Schlegel et al. (SFD) reddening map and find them consistent to within a scatter of ~= 5 mmag. Further, the differences between our map and the SFD map are in excellent agreement with the low-resolution (4\buildrel{\circ}\over{.} 5) corrections to the SFD map derived by Peek and Graves based on observed reddening toward passive galaxies. We therefore argue that our H I-based map provides the most accurate interstellar reddening estimates in the low-column-density regime to date. Our reddening map is made publicly available at doi.org/10.7910/DVN/AFJNWJ.

Lenz, Daniel; Hensley, Brandon S.; Doré, Olivier
2017, The Astrophysical Journal, 846, 38

Figure 1. We plot the total H I column density in each pixel against the reddening in that pixel as measured from stellar data by S14 (left) and from FIR dust emission by SFD (right). Note that the S14 comparison is limited to the S14 footprint, whereas the SFD comparison covers the full sky. The top panels show the data on a linear scale and restricted to NHI < 4 x 10^20 cm−2, while the bottom panels are logarithmically scaled and demonstrate the deviation from linearity at high NH I. The blue line indicates the fit to the data for NH I < 4 x 10^20 cm−2 (solid) and is extrapolated to higher column densities (dashed).[/caption]