Deep HI observations of the outer parts of disc galaxies demonstrate the frequent presence of extended, well-developed spiral arms far beyond the optical radius. To understand the nature and the origin of such outer spiral structure, we investigate the propagation in the outer gaseous disc of large-scale spiral waves excited in the bright optical disc. Using hydrodynamical simulations, we show that non-axisymmetric density waves, penetrating in the gas through the outer Lindblad resonance, can exhibit relatively regular spiral structures outside the bright optical stellar disc. For low-amplitude structures, the results of numerical simulations match the predictions of a simple WKB linear theory. The amplitude of spiral structure increases rapidly with radius. Beyond ≈2 optical radii, spirals become non-linear (the linear theory becomes quantitatively and qualitatively inadequate) and unstable. In numerical simulations, in models for which gas is available very far out, spiral arms can extend out to 25 disc scalelengths. A comparison between the properties of the models we have investigated and the observed properties of individual galaxies may shed light into the problem of the amount and distribution of dark matter in the outer halo.

Spiral density waves in the outer galactic gaseous discs / S.A. Khoperskov, G. Bertin. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - 451:3(2015 Aug), pp. 2889-2899. [10.1093/mnras/stv1145]

Spiral density waves in the outer galactic gaseous discs

G. Bertin
Ultimo
2015

Abstract

Deep HI observations of the outer parts of disc galaxies demonstrate the frequent presence of extended, well-developed spiral arms far beyond the optical radius. To understand the nature and the origin of such outer spiral structure, we investigate the propagation in the outer gaseous disc of large-scale spiral waves excited in the bright optical disc. Using hydrodynamical simulations, we show that non-axisymmetric density waves, penetrating in the gas through the outer Lindblad resonance, can exhibit relatively regular spiral structures outside the bright optical stellar disc. For low-amplitude structures, the results of numerical simulations match the predictions of a simple WKB linear theory. The amplitude of spiral structure increases rapidly with radius. Beyond ≈2 optical radii, spirals become non-linear (the linear theory becomes quantitatively and qualitatively inadequate) and unstable. In numerical simulations, in models for which gas is available very far out, spiral arms can extend out to 25 disc scalelengths. A comparison between the properties of the models we have investigated and the observed properties of individual galaxies may shed light into the problem of the amount and distribution of dark matter in the outer halo.
Galaxies: kinematics and dynamics; Galaxies: spiral; Galaxies: structure
Settore FIS/05 - Astronomia e Astrofisica
   EVOLUZIONE CHIMICA E DINAMICA DELLA NOSTRA GALASSIA E DELLE GALASSIE DEL GRUPPO LOCALE
   MINISTERO DELL'ISTRUZIONE E DEL MERITO
   2010LY5N2T_002
ago-2015
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/389597
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