Reexamination of the Infrared Excess-Ultraviolet Slope Relation of Local 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 (β) 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 IRXβ relation depending on sample selection. We reexamined the IRX-β relation by measuring the farand 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 λ = 42-122 µm, using the data from AKARI which has wider wavelength coverage toward longer wavelengths, we obtained an appropriate IRX-β relation with total dust emission (TIR): log (L TIR /L FUV ) = log 10 0.4(3.06+1.58β) − 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.

The galaxy luminosity function atz≃ 6and evidence for rapid evolution in the bright end fromz≃ 7to5

“…The rest-frame UV slope can be linked to the predicted attenuation in the rest-frame UV according to the 'IRX-βUV relation' (Meurer et al 1999), where the IRX is the 'infrared excess' and is given by LIR/LUV. While a βUV −2.0 as observed at z 7 suggest little or no dust attenuation, if the updated relation of Takeuchi et al (2012) is assumed, we predict an attenuation in the range AUV 1.5-0.7 for rest-frame UV slopes of βUV = −1.0 to −1.5 (as we observe in some of the brightest galaxies in our sample). The predicted total far-infrared luminosity implied for objects in this βUV range according to the IRX-βUV relation is LTIR 0.4-1.5 × 10 11 L , similar to the observed luminosity of two z 6 galaxies found by Willott et al (2015).…”

A Statistical and Multi-wavelength Study of Star Formation in Galaxies

“…It turns out that, in spite of all these (sometimes crude) assumptions, the end result is on average in good agreement with the more direct estimates obtained from the FIR luminosity of local galaxies , although some correction were later published (Takeuchi et al 2012). This puzzling agreement probably shows that although each galaxy is unique in its detailed properties and structure, most of the differences are washed out when averaging quantities over the whole volume of the galaxy 10 .…”

Trident: A three-pronged galaxy survey

“…The GALEX IRX ratios used by Meurer et al (1999) are believed to have been overestimated (Overzier et al 2011;Takeuchi et al 2012). We show for comparison the new relation derived for local galaxies as presented by Takeuchi et al (2012), and the relation derived for z ∼ 1−2 sources from Buat et al (2012). In the right panel of Fig.…”

“…Reddy et al (2010), to convert from L FIR to the total L IR . Also shown are the more recent Takeuchi et al (2012) and Buat et al (2012) β-IRX relations, derived for local galaxies and z ∼ 1−2 sources, respectively. Right panel: IRX vs. bolometric luminosity for the same candidates, compared to the sample of BzK selected galaxies from Daddi et al (2007) and the empirical relation for BM/BX-selected galaxies found by Reddy et al (2006).…”