Galaxy Zoo: star formation versus spiral arm numberTools Hart, Ross E., Bamford, Steven P., Casteels, Kevin R.V., Kruk, Sandor J., Lintott, Chris J. and Masters, Karen L. (2017) Galaxy Zoo: star formation versus spiral arm number. Monthly Notices of the Royal Astronomical Society, 468 (2). pp. 1850-1863. ISSN 1365-2966 Full text not available from this repository.
Official URL: https://doi.org/10.1093/mnras/stx581
AbstractSpiral 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.
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