Structure and dynamics of galaxies with a low surface brightness disc. I. The stellar and ionised-gas kinematics

TL;DR

This study investigates the stellar and ionised-gas kinematics of six low surface brightness disc galaxies, revealing that stellar motions are more regular than gas motions, which often show complex, non-circular behaviors affecting mass modeling accuracy.

Contribution

It provides detailed kinematic measurements along multiple axes for low surface brightness galaxies, highlighting differences between stellar and gas motions and questioning gas as a reliable tracer for mass distribution.

Findings

Stellar kinematics are more regular than ionised-gas kinematics.

Ionised gas often exhibits non-circular and off-plane motions.

Kinematic data extend to the flat part of the rotation curve at mu_R~24 mag/arcsec^2.

Abstract

(abridged) Photometry and long-slit spectroscopy are presented for a sample of 6 galaxies with a low surface brightness stellar disc and a bulge. The stellar and ionised-gas kinematics were measured along the major and minor axis in half of the sample galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level mu_R~24mag/arcsec^2 reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionised-gas kinematics, which often shows the presence of non-circular, off-plane, and non-ordered motions. This raises the question about the reliability of the use of the ionised gas as the tracer of the circular velocity in the modeling of the mass distribution, in particular in the central regions of low surface brightness galaxies.