On the Connection Between Spiral Arm Pitch Angle and Galaxy Properties

Abstract

We measure the pitch angle ($\phi$) of spiral arms in a sample of 79 galaxies to perform a systematic study of the dependence of $\phi$ on galaxy morphology, mass, and kinematics to investigate the physical origin of spiral arms. We find that $\phi$ decreases (arms are more tightly wound), albeit with significant scatter, in galaxies with earlier Hubble type, more prominent bulges, higher concentration, and larger total galaxy stellar mass ($M_{\ast }^{\mathrm{gal}}$). For a given concentration, galaxies with larger stellar masses tend to have tighter spiral arms, and vice versa. We also find that $\phi$ obeys a tight inverse correlation with central stellar velocity dispersion for ${\sigma }_c$$\gtrsim$$100$ km s${}^{-1}$, whereas $\phi$ remains approximately constant for ${\sigma }_c\lesssim 100$ km s${}^{-1}$. We demonstrate that the $\phi$-${\sigma }_c$ and $\phi$-$M_{\ast }^{\mathrm{gal}}$ relations are projections of a more fundamental three-dimensional $\phi -{\sigma }_c-M_{\ast }^{\mathrm{gal}}$ relation, such that pitch angle is determined by ${\sigma }_c$ for massive galaxies but by $M_{\ast }^{\mathrm{gal}}$ for less massive galaxies. Contrary to previous studies, we find that $\phi$ correlates only loosely with the galaxy's shear rate. For a given shear rate, spirals generated from $N$-body simulations exhibit much higher $\phi$ than observed, suggesting that galactic disks are dynamically cooler (Toomre's $Q\approx 1.2$). Instead, the measured pitch angles show a much stronger relation with morphology of the rotation curve of the central region, such that galaxies with centrally peaked rotation curves have tight arms, while those with slow-rising rotation curves have looser arms. These behaviors are qualitatively consistent with predictions of density wave theory.

16 pages, 12 figures, 1 table; ApJ in press

References in corpus (16)

• Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics
• Dawes Review 4: Spiral Structures in Disc Galaxies
• CALIFA: a diameter-selected sample for an integral field spectroscopy galaxy survey
• Stellar kinematics across the Hubble sequence in the CALIFA survey: General properties and aperture corrections
• Two-dimensional multi-component photometric decomposition of CALIFA galaxies
• Discovery of a relationship between spiral arm morphology and supermassive black hole mass in disk galaxies
• Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. I. Method outline
• Star formation in the local Universe from the CALIFA sample. II. Activation and quenching mechanisms in bulges, bars, and disks
• An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies
• Galaxy Zoo and SpArcFiRe: Constraints on spiral arm formation mechanisms from spiral arm number and pitch angles
• Spiral structure in nearby galaxies II. comparative analysis and conclusions
• Dependence of Spiral Arms Pitch Angle on Wavelength as a Test of Density Wave Theory
• The Carnegie-Irvine Galaxy Survey. VI. Quantifying Spiral Structure
• Pitch Angle of Galactic Spiral Arms
• The behavior of the pitch angle of spiral arms depending on optical wavelength
• An Extensive Photometric Catalog of CALIFA Galaxies

Cited by in corpus (9)

• Spirals in galaxies
• The shapes of spiral arms in the S${}^4$G survey and their connection with stellar bars
• The Carnegie-Irvine Galaxy Survey. VIII. Demographics of Bulges along the Hubble Sequence
• A Consistent Set of Empirical Scaling Relations for Spiral Galaxies: The $(v_{\max },M_{\mathrm{DM}})$-$({\sigma }_0,M_{\mathrm{BH}},\varphi )$ Relations
• What is Important? Morphological Asymmetries are Useful Predictors of Star Formation Rates of Star-forming Galaxies in SDSS Stripe 82
• Galaxy Zoo Builder: Morphological Dependence of Spiral Galaxy Pitch Angle
• Evidence in favour of density wave theory through star formation history maps and spatially resolved stellar clusters
• Precessing ellipses as the building blocks of spiral arms
• Elementary Process of Galactic Spiral Arm Formation: Phase Synchronization of Epicyclic Motion by Gravitational Scattering