Resolving the Disc-Halo Degeneracy II: NGC 6946

Abstract

The mass-to-light ratio (M/L) is a key parameter in decomposing galactic rotation curves into contributions from the baryonic components and the dark halo of a galaxy. One direct observational method to determine the disc M/L is by calculating the surface mass density of the disc from the stellar vertical velocity dispersion and the scale height of the disc. Usually, the scale height is obtained from near-IR studies of edge-on galaxies and pertains to the older, kinematically hotter stars in the disc, while the vertical velocity dispersion of stars is measured in the optical band and refers to stars of all ages (up to ~10 Gyr) and velocity dispersions. This mismatch between the scale height and the velocity dispersion can lead to underestimates of the disc surface density and a misleading conclusion of the sub-maximality of galaxy discs. In this paper we present the study of the stellar velocity dispersion of the disc galaxy NGC 6946 using integrated star light and individual planetary nebulae as dynamical tracers. We demonstrate the presence of two kinematically distinct populations of tracers which contribute to the total stellar velocity dispersion. Thus, we are able to use the dispersion and the scale height of the same dynamical population to derive the surface mass density of the disc over a radial extent. We find the disc of NGC 6946 to be closer to maximal with the baryonic component contributing most of the radial gravitational field in the inner parts of the galaxy (Vmax(bar) = 0.76($\pm$0.14)Vmax).

17 pages, 14 figures, Accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1802.00465

References in corpus (13)

• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• HI holes and high-velocity clouds in the spiral galaxy NGC 6946
• Planetary Nebulae in Face-On Spiral Galaxies. I. Planetary Nebula Photometry and Distances
• The inner structure of haloes in Cold+Warm dark matter models
• From light to baryonic mass: the effect of the stellar mass-to-light ratio on the Baryonic Tully-Fisher relation
• The Multi-Wavelength Tully-Fisher relation with spatially resolved HI kinematics
• Stellar population synthesis models between 2.5 and 5 μm based on the empirical IRTF stellar library
• A revised planetary nebula luminosity function distance to NGC 628 using MUSE
• Detailed HI kinematics of Tully-Fisher calibrator galaxies
• CO(1-0), CO(2-1) and Neutral Gas in NGC 6946: Molecular Gas in a Late-Type, Gas Rich, Spiral Galaxy
• The Link Between Light and Mass in Late-type Spiral Galaxy Disks
• The survey of Planetary Nebulae in Andromeda (M31): I. Imaging the disk and halo with MegaCam@CFHT

Cited by in corpus (12)

• From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity
• Planetary Nebulae: Sources of Enlightenment
• Stellar Mass-to-light Ratios: Composite Bulge+Disk Models and the Baryonic Tully-Fisher Relation
• A preserved high-z compact progenitor in the heart of NGC3311 revealed with MUSE 2D stellar population analysis
• The survey of planetary nebulae in Andromeda (M 31) V. Chemical enrichment of the thin and thicker discs of Andromeda. Oxygen to argon abundance ratios for planetary nebulae and H II regions
• The survey of planetary nebulae in Andromeda (M31). IV. Radial oxygen and argon abundance gradients of the thin and thicker disc
• The survey of planetary nebulae in Andromeda (M31) VI. Kinematics of M31 inner-halo substructures and comparison with major-merger simulation predictions
• How Close Dark Matter Halos and MOND Are to Each Other: Three-Dimensional Tests Based on Gaia DR2
• MUSE crowded field 3D spectroscopy in NGC 300 : IV. Planetary nebula luminosity function
• Bar formation in submaximal discs: a challenge for ΛCDM
• The PICS Project. I. The impact of metallicity and helium abundance on the bright end of the planetary nebula luminosity function
• An Integral Field Spectroscopy Study Of Thin And Thick Discs In IC 2531