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 min per galaxy, assuming 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. All code is freely available.
Additional Information
This research was funded in part by NSF REU Site Award 1157002. The Australian Research Council's funding scheme DP17012923 supported this research. This material is based upon work supported by Tamkeen under the NYU Abu Dhabi Research Institute grant CAP3. We gratefully acknowledge Ivânio Puerari for writing the original 2DFFT code on which the later versions of 2DFFT were based, and also William Ring for visually selecting spirals from the GOODS sample. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of NASA's Astrophysics Data System. Parts of this research were conducted by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), through project number CE170100004.Additional details
- Eprint ID
- 117749
- Resolver ID
- CaltechAUTHORS:20221107-998820100.18
- AST-1157002
- NSF
- DP17012923
- Australian Research Council
- CAP3
- New York University Abu Dhabi
- NASA/JPL/Caltech
- CE170100004
- Australian Research Council
- Created
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2022-11-18Created from EPrint's datestamp field
- Updated
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2022-11-18Created from EPrint's last_modified field