Ultraviolet Extinction at High Galactic Latitudes

TL;DR

This study analyzes ultraviolet and optical data from multiple surveys to characterize high Galactic latitude dust extinction, revealing deviations from standard reddening laws and suggesting an increase in small silicate grains.

Contribution

It provides the first detailed measurement of the high-latitude extinction curve across UV and optical wavelengths, highlighting its differences from standard models.

Findings

UV extinction is ~10% higher than expected

Optical extinction is ~35% higher than expected

No single R_V value fits both UV and optical data

Abstract

In order to study the properties and effects of high Galactic latitude dust we present an analysis of 373,303 galaxies selected from the Galaxy Evolution Explorer (GALEX) All-Sky Survey and Wide-Field Infrared Explorer (WISE) All-Sky Data Release. By examining the variation in aggregate ultraviolet colors and number density of these galaxies we measure the extinction curve at high latitude. We additionally consider a population of spectroscopically selected galaxies from the Sloan Digital Sky Survey (SDSS) to measure extinction in the optical. We find that dust at high latitude is neither quantitatively nor qualitatively consistent with standard reddening laws. Extinction in the FUV and NUV is ~10% and ~35% higher than expected, with significant variation across the sky. We find that no single R_V parameter fits both the optical and ultraviolet extinction at high latitude, and that while both show detectable variation across the sky, these variations are not related. We propose that the overall trends we detect likely stem from an increase in very small silicate grains in the ISM.