GALEX Absolute Calibration and Extinction Coefficients Based on White Dwarfs

TL;DR

This study uses a large sample of white dwarfs with Gaia data to verify and refine the absolute calibration and extinction coefficients for GALEX ultraviolet observations, providing improved understanding of dust extinction in the Milky Way.

Contribution

The paper presents new, precise measurements of GALEX extinction coefficients using white dwarfs, confirming the linearity correction limits and offering the most accurate constraints to date.

Findings

Linearity correction valid for magnitudes brighter than 15.95 (FUV) and 16.95 (NUV).

Extinction coefficients: R_FUV=8.01±0.07, R_NUV=6.72±0.04.

Extinction coefficients align with Milky Way dust models in FUV, but are smaller in NUV.

Abstract

We use 1837 DA white dwarfs with high signal to noise ratio spectra and Gaia parallaxes to verify the absolute calibration and extinction coefficients for the Galaxy Evolution Explorer (GALEX). We use white dwarfs within 100 pc to verify the linearity correction to the GALEX data. We find that the linearity correction is valid for magnitudes brighter than 15.95 and 16.95 for the Far Ultraviolet (FUV) and Near Ultraviolet (NUV) bands, respectively. We also use DA white dwarfs beyond 250 pc to calculate extinction coefficients in the FUV and NUV bands; $R_{\rm FUV}=8.01 \pm 0.07$ and $R_{\rm NUV}=6.72 \pm 0.04$. These are consistent with the predicted extinction coefficients for Milky Way type dust in the FUV, but smaller than predictions in the NUV. With well understood optical spectra and state-of-the-art model atmosphere analysis, these white dwarfs currently provide the best constraints on the extinction coefficients for the GALEX data.