Characterizing Ultraviolet and Infrared Observational Properties for Galaxies. I. Influences of Dust Attenuation and Stellar Population Age

TL;DR

This study investigates how dust attenuation and stellar population age influence the IRX-UV relation in galaxies, revealing that multiple factors and spatial variations contribute to the observed dispersion, and emphasizing the need for additional parameters in models.

Contribution

It introduces a spatially resolved analysis of nearby galaxies, highlighting the roles of dust, age, and other parameters in shaping the IRX-UV relation, and suggests that integrated galaxy measurements can mask these effects.

Findings

Stellar population age affects the IRX-UV relation.

Variations in attenuation law contribute to dispersion.

Spatial distributions of UV color and IRX differ within galaxies.

Abstract

The correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color, i.e. the IRX-UV relation, was regarded as a prevalent recipe for correcting extragalactic dust attenuation. Considerable dispersion in this relation discovered for normal galaxies, however, complicates its usability. In order to investigate the cause of the dispersion, in this paper, we select five nearby spiral galaxies, and perform spatially resolved studies on each of the galaxies, with a combination of ultraviolet and infrared imaging data. We measure all positions within each galaxy and divide the extracted regions into young and evolved stellar populations. By means of this approach, we attempt to discover separate effects of dust attenuation and stellar population age on the IRX-UV relation for individual galaxies. In this work, in addition to dust attenuation, stellar population age is interpreted to be another parameter in the IRX-UV function, and the diversity of star formation histories is suggested to disperse the age effects. At the same time, strong evidence shows the necessity of more parameters in the interpretation of observational data, such as variations in attenuation/extinction law. Fractional contributions of different components to the integrated luminosities of the galaxies suggest that the integrated measurements of galaxies which comprise different populations would weaken the effect of the age parameter on IRX-UV diagrams. The dependance of the IRX-UV relation on luminosity and radial distance in galaxies presents weak trends, which offers an implication of selective effects. The two-dimensional maps of the UV color and the infrared-to-ultraviolet ratio are displayed and show a disparity in the spatial distributions between the two parameters in galaxies, which offers a spatial interpretation of the scatter in the IRX-UV relation.