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Galaxy Zoo: star formation versus spiral arm number

Hart, Ross E.; Bamford, Steven P.; Casteels, Kevin R.V.; Kruk, Sandor J.; Lintott, Chris J.; Masters, Karen L.


Ross E. Hart

Steven P. Bamford

Kevin R.V. Casteels

Sandor J. Kruk

Chris J. Lintott

Karen L. Masters


Spiral arms are common features in low-redshift disc galaxies, and are prominent sites of star formation and dust obscuration. However, spiral structure can take many forms: from galaxies displaying two strong ‘grand design’ arms to those with many ‘flocculent’ arms. We investigate how these different arm types are related to a galaxy's star formation and gas properties by making use of visual spiral arm number measurements from Galaxy Zoo 2. We combine ultraviolet and mid-infrared (MIR) photometry from GALEX and WISE to measure the rates and relative fractions of obscured and unobscured star formation in a sample of low-redshift SDSS spirals. Total star formation rate has little dependence on spiral arm multiplicity, but two-armed spirals convert their gas to stars more efficiently. We find significant differences in the fraction of obscured star formation: an additional ∼10 per cent of star formation in two-armed galaxies is identified via MIR dust emission, compared to that in many-armed galaxies. The latter are also significantly offset below the IRX–β relation for low-redshift star-forming galaxies. We present several explanations for these differences versus arm number: variations in the spatial distribution, sizes or clearing time-scales of star-forming regions (i.e. molecular clouds), or contrasting recent star formation histories.


Hart, R. E., Bamford, S. P., Casteels, K. R., Kruk, S. J., Lintott, C. J., & Masters, K. L. (2017). Galaxy Zoo: star formation versus spiral arm number. Monthly Notices of the Royal Astronomical Society, 468(2),

Journal Article Type Article
Acceptance Date Mar 6, 2017
Online Publication Date Mar 8, 2017
Publication Date Jun 30, 2017
Deposit Date Jun 5, 2017
Publicly Available Date Jun 5, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 468
Issue 2
Keywords Galaxies, Galaxies, spiral, Star formation, Structure of galaxies
Public URL
Publisher URL
Additional Information This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


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