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.

Abstract

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.

Citation

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), 1850-1863. https://doi.org/10.1093/mnras/stx581

• 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
• Pages: 1850-1863
• DOI: https://doi.org/10.1093/mnras/stx581
• Keywords: Galaxies, Galaxies, spiral, Star formation, Structure of galaxies
• Public URL: https://nottingham-repository.worktribe.com/output/870326
• Publisher URL: https://doi.org/10.1093/mnras/stx581
• 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.