Spiral arms and disc stability in the Andromeda galaxy

Abstract

Aims: Density waves are often considered as the triggering mechanism of star formation in spiral galaxies. Our aim is to study relations between different star formation tracers (stellar UV and near-IR radiation and emission from HI, CO and cold dust) in the spiral arms of M31, to calculate stability conditions in the galaxy disc and to draw conclusions about possible star formation triggering mechanisms. Methods: We select fourteen spiral arm segments from the de-projected data maps and compare emission distributions along the cross sections of the segments in different datasets to each other, in order to detect spatial offsets between young stellar populations and the star forming medium. By using the disc stability condition as a function of perturbation wavelength and distance from the galaxy centre we calculate the effective disc stability parameters and the least stable wavelengths at different distances. For this we utilise a mass distribution model of M31 with four disc components (old and young stellar discs, cold and warm gaseous discs) embedded within the external potential of the bulge, the stellar halo and the dark matter halo. Each component is considered to have a realistic finite thickness. Results: No systematic offsets between the observed UV and CO/far-IR emission across the spiral segments are detected. The calculated effective stability parameter has a minimal value Q_{eff} ~ 1.8 at galactocentric distances 12 - 13 kpc. The least stable wavelengths are rather long, with the minimal values starting from ~ 3 kpc at distances R > 11 kpc. Conclusions: The classical density wave theory is not a realistic explanation for the spiral structure of M31. Instead, external causes should be considered, e.g. interactions with massive gas clouds or dwarf companions of M31.

12 pages, 8 figures, Astron & Astrophys accepted

References in corpus (20)

• Dawes Review 4: Spiral Structures in Disc Galaxies
• On the Rapid Collapse and Evolution of Molecular Clouds
• The long bar as seen by the VVV survey: I. Colour-magnitude diagrams
• A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
• Observational Evidence of Dynamic Star Formation Rate in Milky Way Giant Molecular Clouds
• Kinematics of Spiral Arm Streaming in M51
• Geometrically Derived Timescales for Star Formation in Spiral Galaxies
• Physical Properties of Tidal Features in Interacting Disk Galaxies
• A clear age-velocity dispersion correlation in Andromeda's stellar disk
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) VII: A SKIRT radiative transfer model and insights on dust heating
• Radial Dependence of the Pattern Speed of M51
• The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
• Spiral structure in nearby galaxies II. comparative analysis and conclusions
• Signatures of the M31-M32 Galactic Collision
• Strong Evidence for the Density-wave Theory of Spiral Structure in Disk Galaxies
• The effect of ISM turbulence on the gravitational instability of galactic discs
• Gas and stellar spiral arms and their offsets in the grand-design spiral galaxy M51
• Geometric Offsets Across Spiral Arms in M51: Nature of Gas and Star Formation Tracers
• Radial distributions of arm-gas offsets as an observational test of spiral theories
• SDSS surface photometry of M 31 with absorption corrections

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• Spiral-arm instability: giant clump formation via fragmentation of a galactic spiral arm
• The M31/M33 tidal interaction: A hydrodynamic simulation of the extended gas distribution
• The Complex Structure of the Bulge of M31
• M31 circum-nuclear region: a molecular survey with the IRAM-interferometer
• Are disks of satellites comprised of tidal dwarf galaxies?
• A comprehensive catalogue of OB cluster candidates in M31 and their association with giant molecular clouds