# Revealing strong bias in common measures of galaxy properties using new inclination-independent structures

## TL;DR

This paper demonstrates that common galaxy structure metrics are strongly biased by inclination and dust, and introduces new inclination-independent measures to improve the accuracy of galaxy property assessments.

## Contribution

The authors develop novel inclination-independent galaxy structure metrics by collapsing light distributions, reducing bias in size and concentration measurements.

## Key findings

- Inclination significantly affects traditional galaxy metrics.
- New inclination-independent measures reduce bias in galaxy property analysis.
- Systematic effects of inclination impact star formation and metallicity estimates.

## Abstract

Accurate measurement of galaxy structures is a prerequisite for quantitative investigation of galaxy properties or evolution. Yet, the impact of galaxy inclination and dust on commonly used metrics of galaxy structure is poorly quantified. We use infrared data sets to select inclination-independent samples of disc and flattened elliptical galaxies. These samples show strong variation in S\'{e}rsic index, concentration, and half-light radii with inclination. We develop novel inclination-independent galaxy structures by collapsing the light distribution in the near-infrared on to the major axis, yielding inclination-independent `linear' measures of size and concentration. With these new metrics we select a sample of Milky Way analogue galaxies with similar stellar masses, star formation rates, sizes and concentrations. Optical luminosities, light distributions, and spectral properties are all found to vary strongly with inclination: When inclining to edge-on, $r$-band luminosities dim by $>$1 magnitude, sizes decrease by a factor of 2, `dust-corrected' estimates of star formation rate drop threefold, metallicities decrease by 0.1 dex, and edge-on galaxies are half as likely to be classified as star forming. These systematic effects should be accounted for in analyses of galaxy properties.