A Comparison of Far IR and HI as Reddening Predictors at High Galactic Latitude

TL;DR

This study compares the effectiveness of HI 21-cm line flux and far-infrared emission in predicting Galactic reddening at high latitudes, finding that combining both methods yields more accurate results.

Contribution

It demonstrates that a combined approach using both FIR and HI data improves reddening estimates over individual methods.

Findings

Both methods produce reasonably accurate reddening maps.

Significant errors exist in both methods individually.

A 2-to-1 combination of FIR and HI maps outperforms either alone.

Abstract

Both the Galactic 21-cm line flux from neutral hydrogen (HI) in interstellar medium and the far-infrared (FIR) emission from Galactic dust grains have been used to estimate the strength of Galactic reddening of distant sources. In this work we use a collection of uniform color distant galaxies as color standards to determine whether the HI method or the FIR method is superior. We find that the two methods both produce reasonably accurate maps, but that both show significant errors as compared to the typical color of the background galaxies. We find that a mixture of the FIR and HI maps in roughly a 2-to-1 ratio is clearly superior to either map alone. We recommend that future reddening maps should use both sets of data, and that well-constructed FIR and HI maps should both be vigorously pursued.