Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

Abstract

We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 minutes per galaxy, assuming at least 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code's results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality's error bars overlapped 2DFFT's error bars for 26 of the 30 galaxies. The two methods' agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies' spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. The code package is freely available online; see Comments for URL.

19 pages, 9 figures, 3 tables. The code package is available at http://dafix.uark.edu/~doug/SpiralityCode/

References in corpus (11)

• Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
• Discovery of a relationship between spiral arm morphology and supermassive black hole mass in disk galaxies
• Updating the (Supermassive Black Hole Mass) - (Spiral Arm Pitch Angle) Relation: A Strong Correlation for Galaxies with Pseudobulges
• Strong Evidence for the Density-wave Theory of Spiral Structure in Disk Galaxies
• Disk-stability constraints on the number of arms in spiral galaxies
• A Fundamental Plane of Spiral Structure in Disk Galaxies
• A Consistent Set of Empirical Scaling Relations for Spiral Galaxies: The $(v_{\max },M_{\mathrm{DM}})$-$({\sigma }_0,M_{\mathrm{BH}},\varphi )$ Relations
• A new method to estimate local pitch angles in spiral galaxies: Application to spiral arms and feathers in M81 and M51
• Investigating the Origins of Spiral Structure in Disk Galaxies through a Multiwavelength Study
• The behavior of the pitch angle of spiral arms depending on optical wavelength
• Smoothing Rotation Curves and Mass Profiles

Cited by in corpus (10)

• Updating the (Supermassive Black Hole Mass) - (Spiral Arm Pitch Angle) Relation: A Strong Correlation for Galaxies with Pseudobulges
• Strong Evidence for the Density-wave Theory of Spiral Structure in Disk Galaxies
• A multi-wavelength study of spiral structure in galaxies. I. General characteristics in the optical
• Spiral arm formation mechanisms: Spiral Structure in Barred galaxies. Observational constraints to spiral arm formation mechanisms
• Searching for Intermediate Mass Black Holes in galaxies with Low Luminosity AGN: A multiple-method approach
• The AGN Ionization Cones of NGC 5728 : II - Kinematics
• Determining the Co-Rotation Radii of Spiral Galaxies Using Spiral Arm Pitch Angle Measurements at Multiple Wavelengths
• Discovery of a Planar Black Hole Mass Scaling Relation for Spiral Galaxies
• Probing the Low-mass End of the Black Hole Mass Function via a Study of Faint Local Spiral Galaxies
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies