skip to main content

Title: A new method to estimate local pitch angles in spiral galaxies: Application to spiral arms and feathers in M81 and M51

We examine 8 μm IRAC images of the grand design two-arm spiral galaxies M81 and M51 using a new method whereby pitch angles are locally determined as a function of scale and position, in contrast to traditional Fourier transform spectral analyses which fit to average pitch angles for whole galaxies. The new analysis is based on a correlation between pieces of a galaxy in circular windows of (lnR,θ) space and logarithmic spirals with various pitch angles. The diameter of the windows is varied to study different scales. The result is a best-fit pitch angle to the spiral structure as a function of position and scale, or a distribution function of pitch angles as a function of scale for a given galactic region or area. We apply the method to determine the distribution of pitch angles in the arm and interarm regions of these two galaxies. In the arms, the method reproduces the known pitch angles for the main spirals on a large scale, but also shows higher pitch angles on smaller scales resulting from dust feathers. For the interarms, there is a broad distribution of pitch angles representing the continuation and evolution of the spiral arm feathers as the flowmore » moves into the interarm regions. Our method shows a multiplicity of spiral structures on different scales, as expected from gas flow processes in a gravitating, turbulent and shearing interstellar medium. We also present results for M81 using classical 1D and 2D Fourier transforms, together with a new correlation method, which shows good agreement with conventional 2D Fourier transforms.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Instituto Nacional de Astrofísica, Optica y Electrónica, Calle Luis Enrique Erro 1, 72840 Santa María Tonantzintla, Puebla (Mexico)
  2. IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598 (United States)
  3. School of Computational and Applied Mathematics, University of Witwatersrand, Private Bag 3, WITS 2050 (South Africa)
Publication Date:
OSTI Identifier:
22342197
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 148; Journal Issue: 6; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ARMS; CORRELATIONS; DESIGN; DISTRIBUTION; DISTRIBUTION FUNCTIONS; DUSTS; EVOLUTION; FOURIER TRANSFORMATION; GALAXIES; GAS-FLOW PROCESSES; IMAGES; INCLINATION; MULTIPLICITY; SPACE; SPIRAL CONFIGURATION