Role of gas in supporting grand spiral structure

Abstract

The density wave theory for the grand-design two-armed spiral pattern in galaxies is successful in explaining several observed features. However, the long-term persistence of this spiral structure is a serious problem since the group transport would destroy it within about a billion years as shown in a classic paper by Toomre. In this paper we include the low velocity dispersion component, namely gas, on an equal footing with stars in the formulation of the density wave theory, and obtain the dispersion relation for this coupled system. We show that the inclusion of gas makes the group transport slower by a factor of few, thus allowing the pattern to persist longer - for several billion years. Though still less than the Hubble time, this helps in making the spiral structure more long-lived. Further we show that addition of gas is essential to get a stable wave for the observed pattern speed for the Galaxy, which otherwise is not possible for a one-component stellar disc.

6 pages, 3 figures, 1 table, accepted for publication in MNRAS

References in corpus (3)

• Dawes Review 4: Spiral Structures in Disc Galaxies
• Slowly Breaking Waves: The Longevity of Tidally Induced Spiral Structure
• A new method for estimating the pattern speed of spiral structure in the Milky Way

Cited by in corpus (16)

• Galaxy Zoo and SpArcFiRe: Constraints on spiral arm formation mechanisms from spiral arm number and pitch angles
• The Carnegie-Irvine Galaxy Survey. VI. Quantifying Spiral Structure
• Stellar metallicity variations across spiral arms in disk galaxies with multiple populations
• The most ancient spiral galaxy: a 2.6-Gyr-old disk with a tranquil velocity field
• Galaxy Zoo: star-formation versus spiral arm number
• Bars and boxy/peanut bulges in thin and thick discs. II. Can bars form in hot thick discs?
• Excitation of vertical breathing motion in disc galaxies by tidally-induced spirals in fly-by interactions
• The Morphological Transformation of Red Sequence Galaxies in Clusters since $z\sim 1$
• Age dissection of the vertical breathing motions in Gaia DR2: evidence for spiral driving
• Dynamical effect of gas on spiral pattern speed in galaxies
• Bars and boxy/peanut bulges in thin and thick discs III. Boxy/peanut bulge formation and evolution in presence of thick discs
• Identification of Grand-design and Flocculent Spirals from SDSS using Convolutional Neural network
• Effect of dark matter halo on global spiral modes in galaxies
• Local Stability of Galactic Discs in Modified Dynamics
• Effect of dark matter halo on global spiral modes in a collisionless galactic disc
• Dynamical interplay of disc thickness and the interstellar gas: implication for the longevity of spiral density waves