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Interstellar Extinction Curve Variations Toward the Inner Milky Way: A Challenge to Observational Cosmology
Preprint   Open access

Interstellar Extinction Curve Variations Toward the Inner Milky Way: A Challenge to Observational Cosmology

David M Nataf, Oscar A Gonzalez, Luca Casagrande, Gail Zasowski, Christopher Wegg, Christian Wolf, Andrea Kunder, Javier Alonso-Garcia, Dante Minniti, Marina Rejkuba, …
ArXiv.org
Cornell University
12/18/2015
DOI: 10.48550/arxiv.1510.01321
url
https://doi.org/10.48550/arxiv.1510.01321View
Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

We investigate interstellar extinction curve variations toward ∼4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III and VVV surveys, with supporting evidence from diffuse interstellar bands and F435W,F625W photometry. We obtain independent measurements toward ∼2,000 sightlines of AI, E(V−I), E(I−J), and E(J−Ks), with median precision and accuracy of 2%. We find that the variations in the extinction ratios AI/E(V−I), E(I−J)/E(V−I) and E(J−Ks)/E(V−I) are large (exceeding 20%), significant, and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve has at least two degrees of freedom, and not one (e.g. RV), which we conform with a principal component analysis. We derive a median value of <AV/AKs>=13.44, which is ∼60% higher than the "standard" value. We show that the Wesenheit magnitude WI=I−1.61(I−J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ∼100%, and lack sensitivity to extinction curve variations.
Physics - Astrophysics of Galaxies Physics - Cosmology and Nongalactic Astrophysics Physics - Solar and Stellar Astrophysics

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