# One Relation for All Wavelengths: The Far-Ultraviolet to Mid-Infrared Milky Way Spectroscopic R(V) Dependent Dust Extinction Relationship

**Authors:** Karl D. Gordon, Geoffrey C. Clayton, Marjorie Decleir, E. L. Fitzpatrick, Derck Massa, Karl A. Misselt, Erik J. Tollerud  
**arXiv:** [2304.01991](https://arxiv.org/abs/2304.01991)  
**Date:** 2023-04-04  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.01991v1/

## Key points

- Dust extinction is a measurement of dust grain properties such as sizes, compositions, and shapes
- Milky Way extinction variations are strongly correlated with R(V)=A(V)/E(B-V)
- Existing R(V) dependent extinction relationships use a mixture of spectroscopic and photometry observations that do not fully capture all the important dust features nor continuum variations
- The authors consistently measure the R(V) dependent extinction relationship spectroscopically from far-ultraviolet to mid-infrared for the first time using four existing samples of spectroscopically measured dust extinction curves
- Linear fits of A(lambda)/A(V) dependent on R(V) using a method that fully accounts for their significant and correlated uncertainties are used to determine a smooth R(V)-dependent (2.3–5.6) and wavelength (912 Å–32 μm) extinction relationship
- This relationship shows that the far-UV rise, 2175 Å bump, and three broad optical features are dependent on R(V), but the 10 and 20 μm features are not
- Existing literature relationships show significant deviations compared to this relationship especially in the far-ultraviolet and infrared
- Extinction curves that deviate from this relationship illustrate that it only describes average behavior versus R(V)
- There is tentative evidence that the relationship may not be linear with 1/R(V), particularly in the ultraviolet
- This study provides measurements of dust extinction that spectroscopically resolve continuum and features in ultraviolet, optical, and infrared as a function of R(V)
- The four samples used provide full spectroscopic coverage from 912 Å to 32 μm for a broad range of R(V) values
- The authors have not used sightlines known to probe dense ISM as defined by 3 μm ice absorption feature presence
- Comparison to previous R(V)-dependent relationships, examples of deviation from said relationship, and discussion about possible nonlinearities with respect to 1/R(v) are also provided in this paper.

## Summary

Dust extinction is a fundamental measurement of dust grain properties such as sizes, compositions, and shapes. The variations in Milky Way extinction are strongly correlated with the single parameter R(V)=A(V)/E(B-V). However, existing R(V) dependent extinction relationships use a mixture of spectroscopic and photometry observations that do not fully capture all the important dust features nor continuum variations. In this paper, using four existing samples of spectroscopically measured dust extinction curves, the authors consistently measure the R(V) dependent extinction relationship spectroscopically from far-ultraviolet to mid-infrared for the first time. The authors use linear fits of A(lambda)/A(V) dependent on R(V) using a method that fully accounts for their significant and correlated uncertainties. These linear parameters are fit with analytic wavelength-dependent functions to determine a smooth R(V)-dependent (2.3–5.6) and wavelength (912 Å–32 μm) extinction relationship. This relationship shows that the far-UV rise, 2175 Å bump, and three broad optical features are dependent on R(V), but the 10 and 20 μm features are not. Existing literature relationships show significant deviations compared to this relationship especially in the far-ultraviolet and infrared. Extinction curves that deviate from this relationship illustrate that it only describes average behavior versus R(V). There is tentative evidence that the relationship may not be linear with 1/R(V), particularly in the ultraviolet. For the first time, this study provides measurements of dust extinction that spectroscopically resolve continuum and features in ultraviolet, optical, and infrared as a function of R(V). This enables detailed studies of dust grain properties and full spectroscopic accounting for effects of dust extinction on astrophysical objects. The four samples used provide full spectroscopic coverage from 912 Å to 32 μm for a broad range of R(V) values. The authors have not used sightlines known to probe dense ISM as defined by 3 μm ice absorption feature presence. This study provides an comprehensive description of dust extinction from FUV to MIR which can be useful in understanding different environments. Comparison to previous R(V)-dependent relationships, examples of deviation from said relationship, and discussion about possible nonlinearities with respect to 1/R(v) are also provided in this paper.