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

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 Sérsic 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.

5 pages, 4 figures, accepted to MNRAS Letters

References in corpus (6)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Structure and star formation in galaxies out to z=3: evidence for surface density dependent evolution and upsizing
• Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS
• The Intrinsic Properties of SDSS Galaxies
• Galaxy And Mass Assembly (GAMA): the wavelength-dependent sizes and profiles of galaxies revealed by MegaMorph
• Modelling the spectral energy distribution of galaxies. IV Correcting apparent disk scalelengths and central surface brightnesses for the effect of dust at optical and near-infrared wavelengths

Cited by in corpus (4)

• The Intrinsic Scatter of Galaxy Scaling Relations
• Evidence for galaxy quenching in the green valley caused by a lack of a circumgalactic medium
• On the Impact of Inclination-Dependent Attenuation on Derived Star Formation Histories: Results from Disk Galaxies in the Great Observatories Origins Deep Survey Fields
• Asymmetry Revisited: The Effect of Dust Attenuation and Galaxy Inclination