University of Oulu

S. Díaz-García, H. Salo, J. H. Knapen and M. Herrera-Endoqui. The shapes of spiral arms in the S⁴G survey and their connection with stellar bars. A&A, 631 (2019) A94.

The shapes of spiral arms in the S⁴G survey and their connection with stellar bars

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Author: Díaz-García, S.1,2; Salo, H.3; Knapen, J. H.1,2,4;
Organizations: 1Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
2Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
3Astronomy Research Unit, University of Oulu, 90014 Oulu, Finland
4Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
5Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, Baja California 22800, Mexico
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.3 MB)
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Language: English
Published: EDP Sciences, 2019
Publish Date: 2020-01-17


Context.: Spiral galaxies are very common in the local Universe, but their formation, evolution, and interplay with bars remain poorly understood after more than a century of astronomical research on the topic.

Aims: We use a sample of 391 nearby galaxies from the S⁴G survey to characterise the winding angle and amplitude of spiral arms as a function of disc properties, such as bar strength, in all kinds of spirals (grand-design, multi-armed, and flocculent).

Methods: We derived global pitch angles in 3.6 μm de-projected images from (i) average measurements of individual logarithmic spiral segments, and (ii) for a subsample of 32 galaxies, from 2D Fourier analyses. The strength of spirals was quantified from the tangential-to-radial force ratio and from the normalised m = 2 Fourier density amplitudes.

Results: In galaxies with more than one measured logarithmic segment, the spiral pitch angle varies on average by ∼10° between segments, but by up to ≳15 − 20°. The distribution of the global pitch angle versus Hubble type (T) is very similar for barred and non-barred galaxies when 1 ≲ T ≲ 5. Most spiral galaxies (> 90%) are barred for T >  5. The pitch angle is not correlated with bar strength, and only weakly with spiral strength. The amplitude of spirals is correlated with bar strength (and less tightly, with bar length) for all types of spirals. The mean pitch angle is hardly correlated with the mass of the supermassive black hole (estimated from central stellar velocity dispersion), with central stellar mass concentration, or with shear, questioning previous results in the literature using smaller samples.

Conclusions: We do not find observational evidence that spiral arms are driven by stellar bars or by invariant manifolds. Most likely, discs that are prone to the development of strong bars are also reactive to the formation of prominent spirals, explaining the observed coupling between bar and spiral amplitudes.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 631
Article number: A94
DOI: 10.1051/0004-6361/201936000
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We acknowledge financial support from the Euro-pean Union’s Horizon 2020 research and innovation programme under MarieSkłodowska-Curie grant agreement No 721463 to the SUNDIAL ITN network,and from the Spanish Ministry of Economy and Competitiveness (MINECO)under grant number AYA2016-76219-P. S.D. acknowledges the financial sup-port from the visitor and mobility program of the Finnish Centre for Astron-omy with ESO (FINCA), funded by the Academy of Finland grant number306531. J.H.K. acknowledges support from the Fundación BBVA under its 2017programme of assistance to scientific research groups, for the project “Usingmachine-learning techniques to drag galaxies from the noise in deep imaging”,and from the Leverhulme Trust through the award of a Visiting Professorshipat LJMU. H.S. acknowledges financial support from the Academy of Finland(grant no: 297738). M.H.E. thanks CONACyT for supporting his postdoctoralposition through the grant number 252531.
EU Grant Number: (721463) SUNDIAL - SUrvey Network for Deep Imaging Analysis and Learning
Academy of Finland Grant Number: 297738
Detailed Information: 297738 (Academy of Finland Funding decision)
Copyright information: © ESO 2019.