Characterizing Ultraviolet and Infrared Observational Properties for Galaxies. II. Features of Attenuation Law

TL;DR

This study investigates how variations in the dust attenuation law affect the IRX-UV relation in galaxies, using spectral modeling and spatially resolved data to interpret deviations and diagnose attenuation features.

Contribution

It introduces a detailed interpretation of IRX-UV deviations based on attenuation law features, including the linear background and 2175 Angstrom bump, supported by spectral synthesis and spatial measurements.

Findings

Attenuation law variations influence IRX-UV relation deviations.

Different attenuation features can be diagnosed in galaxy samples.

Detecting attenuation law parameters is challenging due to observational degeneracies.

Abstract

Variations in the attenuation law have a significant impact on observed spectral energy distributions for galaxies. As one important observational property for galaxies at ultraviolet and infrared wavelength bands, the correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color index (or ultraviolet spectral slope), i.e., the IRX-UV relation (or IRX-beta relation), offered a widely used recipe for correcting dust attenuation in galaxies, but the usability appears to be in doubt now because of considerable dispersion in this relation found by many studies. In this paper, on the basis of spectral synthesis modeling and spatially resolved measurements of four nearby spiral galaxies, we provide an interpretation of the deviation in the IRX-UV relation with variations in the attenuation law. From both theoretical and observational viewpoints, two components in the attenuation curve, the linear background and the 2175 Angstrom bump, are suggested to be the parameters in addition to the stellar population age (addressed in the first paper of this series) in the IRX-UV function; different features in the attenuation curve are diagnosed for the galaxies in our sample. Nevertheless, it is often difficult to ascertain the attenuation law for galaxies in actual observations. Possible reasons for preventing the successful detection of the parameters in the attenuation curve are also discussed in this paper, including the degeneracy of the linear background and the 2175 Angstrom bump in observational channels, the requirement for young and dust-rich systems to study, and the difficulty in accurate estimates of dust attenuations at different wavelength bands.