[Paper Review] Dynamical Constraints on Disk Masses

J. A. Sellwood|arXiv (Cornell University)|Mar 11, 1999

Galaxies: Formation, Evolution, Phenomena2 references3 citations

TL;DR

This paper uses rotation curves of barred and non-barred galaxies to constrain disk mass contributions, showing that stellar disks dominate inner galaxy masses and that dark matter halos in most galaxies have large cores inconsistent with cosmological simulations. Disk infall can compress initial halos to produce such cores, but maximum disk models raise the 'disk-halo conspiracy' problem and conflict with the Tully-Fisher relation's first-parameter nature.

ABSTRACT

While the total interior mass of a galaxy is reasonably well determined by a good rotation curve, the relative contributions from disk, bulge and halo are only weakly constrained by one-dimensional data. Barred galaxies are intrinsically more complicated, but provide much tighter constraints on the disk masses and support the idea that most of the mass in the inner parts of bright galaxies is in their stars. There appears to be no systematic difference in dark matter content between barred and unbarred galaxies, consistent with the theoretical result that the global stability of galaxies with dense centers does not depend on their halo fraction. The rotation curve shapes of lower luminosity and low-surface-brightness galaxies, on the other hand, indicate significant mass in the DM halo even near their centers. We find that most DM halos appear to have large cores, inconsistent with the predictions from cosmological simulations. We also show that such large-core halos can result from compression by disk infall of physically reasonable initial halos. Maximum disks, while apparently required by the data, do seem to present some puzzles; most notably they re-open the old disk-halo ``conspiracy'' issue and incorrectly predict that surface brightness should be a second parameter in the Tully-Fisher relation.

Motivation & Objective

• To determine the relative contributions of disks, bulges, and halos to galaxy mass budgets using dynamical data.
• To investigate whether barred galaxies provide tighter constraints on disk mass than unbarred ones.
• To assess the consistency of observed dark matter halo structures with cosmological simulations.
• To evaluate the implications of maximum disk models for the Tully-Fisher relation and the disk-halo conspiracy problem.

Proposed method

• Analyzes rotation curves of barred and unbarred galaxies to infer mass distributions.
• Uses the dynamical stability of barred galaxies to constrain disk mass fractions.
• Models halo compression by disk infall to explain large-core structures in halos.
• Compares observed halo core radii with predictions from cosmological simulations.
• Applies the Tully-Fisher relation to test whether surface brightness acts as a second parameter under maximum disk assumptions.
• Evaluates the stability of galaxies with dense centers under varying halo fractions.

Experimental results

Research questions

• RQ1 Do barred galaxies provide stronger constraints on disk mass than unbarred galaxies?
• RQ2 Is there a systematic difference in dark matter content between barred and unbarred galaxies?
• RQ3 Do observed dark matter halos in galaxies have large cores, and is this consistent with cosmological simulations?
• RQ4 Can disk infall compress initial halos to produce large-core structures?
• RQ5 Do maximum disk models lead to inconsistencies in the Tully-Fisher relation?

Key findings

• Barred galaxies indicate that most inner mass in bright galaxies is in stars, supporting high disk mass fractions.
• No systematic difference in dark matter content is found between barred and unbarred galaxies.
• Most dark matter halos appear to have large cores, contradicting predictions from cosmological simulations.
• Such large-core halos can be produced by disk infall compressing physically reasonable initial halo profiles.
• Maximum disk models, while consistent with data, reintroduce the disk-halo conspiracy problem.
• Maximum disks incorrectly predict that surface brightness should be a second parameter in the Tully-Fisher relation.