Ultraviolet Extinction at High Galactic Latitudes II: The Ultraviolet Extinction Function

TL;DR

This paper develops a new ultraviolet extinction function for high Galactic latitudes that accounts for dust column dependence, improves color estimation, and reveals biases in existing extinction maps.

Contribution

It introduces a dust-column-dependent UV extinction function that incorporates HI dependence and corrects biases in Planck and SFD maps.

Findings

SFD maps are biased at low E(B-V)

Varying R_FUV improves color estimates

HI dependence yields a superior extinction model

Abstract

We present a dust-column--dependent extinction curve parameters for ultraviolet wavelengths at high Galactic latitudes. This extinction function diverges from previous work in that it takes into account the results of Peek & Schiminovich 2013 (Paper I), which demonstrated that there is more reddening in the GALEX bands than would be otherwise expected for E(B-V) < 0.2. We also test the biases in the Planck and SFD extinction maps, and find that the SFD extinction maps are significantly biased at E(B-V) < 0.2. We find that while an extinction function that that takes into account a varying R_FUV with E(B-V) dramatically improves our estimation of FUV-NUV colors, a fit that also includes HI column density dependence is superior. The ultraviolet extinction function we present here follows the model of Fitzpatrick 1999, varying only the amplitude of the FUV rise parameter to be consistent with the data.