A tale of two galaxies: light and mass in NGC891 and NGC7814

TL;DR

This study compares the mass and light distributions in two edge-on galaxies, NGC891 and NGC7814, revealing that their rotation curves are closely related to their luminous matter, challenging the notion that dark matter dominates in these cases.

Contribution

The paper provides new rotation curves for NGC891 and NGC7814, demonstrating a close relationship between mass and light distributions in these galaxies.

Findings

NGC7814's mass is more centrally concentrated, matching its light distribution.

NGC891's rotation curve can be explained by luminous matter alone up to 15 kpc.

Dark matter is necessary in NGC7814's outer regions due to high M/L ratios.

Abstract

The two edge-on galaxies NGC891 and NGC7814 are representative of two extreme morphologies: the former is disk-dominated while the latter is almost entirely bulge-dominated. It has been argued (van der Kruit 1983) that since the two galaxies, which are optically so different, have similar rotation curves their total mass distributions cannot be related in any way to the light distributions. This would lead to the conclusion that dark matter is the dominating component of the mass. We have derived new rotation curves from recent, high-sensitivity HI observations and have found that the shapes of the rotation curves are significantly different for the two galaxies. They indicate that in NGC7814 the mass is more concentrated to the centre as compared to NGC891. This reflects the distribution of light which is more centrally concentrated in NGC7814 than in NGC891. Mass and light do seem to be closely related. This is confirmed by the analysis of the rotation curves in mass components: solutions close to the maximum light (bulge + disk) do provide excellent fits. In NGC891 bulge and disk can explain the rotation curve without any need for dark matter out to ~15 kpc. In NGC7814 the bulge dominates in the inner parts; further out the rotation curve is well reproduced by a maximum disk but its M/L ratio is excessively high. A substantial dark matter contribution, closely coupled to the luminous component, seems, therefore, necessary.