Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. II. Dark and stellar mass concentrations for 13 nearby face-on galaxies

TL;DR

This study uses spiral arm pitch angles from galaxy images to infer mass distribution and dark matter halo properties, revealing correlations with shear rate and halo concentration in nearby face-on galaxies.

Contribution

It demonstrates that spiral arm morphology can be used to constrain galaxy mass profiles and dark matter halo characteristics using imaging data alone.

Findings

Pitch angles correlate with shear rate in galaxy rotation curves.

Imaging data can probe galactic mass distributions at large look-back times.

Weak correlation between spiral arm pitch angle and halo concentration.

Abstract

We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves. We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. We then use a sample of 13 galaxies, with Spitzer 3.6-$\mu$m imaging data and observed H$\alpha$ rotation curves, to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. Finally we show that there appears to be a trend (albeit a weak correlation) between spiral arm pitch angle and halo concentration. We discuss implications for the suggested link between supermassive black hole (SMBH) mass and dark halo concentration, using pitch angle as a proxy for SMBH mass.