Reexamination of the Infrared Excess-Ultraviolet Slope Relation of Local Galaxies

TL;DR

This study revisits the IRX-eta relation in galaxies using improved UV and IR data, revealing a revised formula that accounts for wider wavelength coverage and correcting previous underestimations, with implications for dust attenuation estimates.

Contribution

The paper provides a revised IRX-eta relation based on GALEX and AKARI data, addressing previous underestimations and expanding the understanding of dust attenuation in various galaxy types.

Findings

Revised IRX-eta relation with wider wavelength coverage.

Lower IRX values due to UV flux underestimation in earlier studies.

Consistent relation for quiescent IR galaxies, different for luminous IR galaxies.

Abstract

The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (\beta) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star forming galaxies especially at high redshifts. Many authors, however, pointed out that there is a significant dispersion and/or deviation from the originally proposed IRX-\beta relation depending on sample selection. We reexamined the IRX-\beta relation by measuring the far- and near-UV flux densities of the original sample galaxies with GALEX and AKARI imaging data, and constructed a revised formula. We found that the newly obtained IRX values were lower than the original relation because of the significant underestimation of the UV flux densities of the galaxies, caused by the small aperture of IUE, Further, since the original relation was based on IRAS data which covered a wavelength range of \lambda = 42--122\mum, using the data from AKARI which has wider wavelength coverage toward longer wavelengths, we obtained an appropriate IRX-\beta relation with total dust emission (TIR): \log(L_{\rm TIR}/L_{\rm FUV}) = \log [10^{0.4(3.06+1.58\beta)}-1] +0.22. This new relation is consistent with most of the preceding results for samples selected at optical and UV, though there is a significant scatter around it. We also found that even the quiescent class of IR galaxies follows this new relation, though luminous and ultraluminous IR galaxies distribute completely differently as well known before.