The effect of disk inclination on the Main Sequence of star forming galaxies

TL;DR

This study investigates how the inclination angle of galaxy disks affects the estimated star formation rates, revealing significant underestimations in edge-on galaxies and implications for understanding galaxy evolution.

Contribution

It demonstrates the impact of disk inclination on SFR estimates and the Main Sequence, highlighting the importance of accounting for inclination effects in galaxy studies.

Findings

Edge-on disks have underestimated SFRs by 0.2 to 0.4 dex.

High-inclination galaxies are more common in the green valley.

Inclination effects slightly flatten the observed Main Sequence.

Abstract

We use the Sloan Digital Sky Survey (SDSS) database to explore the effect of the disk inclination angle on the derived star formation rate (SFR), hence on the slope and width of the Main Sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on disks are underestimated by factors ranging from $\sim$ 0.2 dex for low mass galaxies up to $\sim$ 0.4 dex for high mass galaxies. This results in a substantially flatter MS relation for high-inclination disks compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is relatively minor, given the small fraction of high-inclination disks. However, we also find that galaxies with high-inclination disks represent a non negligible fraction of galaxies populating the so-called green valley, with derived SFRs intermediate between the MS and those of quenched, passively evolving galaxies.