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Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

Shields, Deanna and Boe, Benjamin and Pfountz, Casey and Davis, Benjamin L. and Hartley, Matthew and Miller, Ryan and Slade, Zac and Abdeen, M. Shameer and Kennefick, Daniel and Kennefick, Julia (2022) Spirality: A Novel Way to Measure Spiral Arm Pitch Angle. Galaxies, 10 (5). Art. No. 100. ISSN 2075-4434. doi:10.3390/galaxies10050100.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Shields, Deanna0000-0002-9974-1268
Boe, Benjamin0000-0002-6396-8209
Davis, Benjamin L.0000-0002-4306-5950
Miller, Ryan0000-0003-0999-2168
Slade, Zac0000-0003-2697-0059
Abdeen, M. Shameer0000-0002-8611-5268
Kennefick, Daniel0000-0002-5219-456X
Kennefick, Julia0000-0002-2141-9041
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.
Funding AgencyGrant Number
Australian Research CouncilDP17012923
New York University Abu DhabiCAP3
Australian Research CouncilCE170100004
Issue or Number:5
Record Number:CaltechAUTHORS:20221107-998820100.18
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117749
Deposited By: Research Services Depository
Deposited On:18 Nov 2022 19:03
Last Modified:18 Nov 2022 23:20

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