Type-II surface brightness profiles in edge-on galaxies produced by flares

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Previous numerical studies had apparently ruled out the possibility that flares in galaxy discs could give rise to the apparent breaks in their luminosity profiles when observed edge-on. However the studies have not, until now, analysed this hypothesis systematically using realistic models for the disc, the flare, and the bulge. We revisit this theme by analysing a series of models which sample a wide range of observationally based structural parameters for these three components. Using observational data, we have considered realistic distributions of bulge-to-disc ratios, morphological parameters of bulges and discs, vertical scale heights of discs and their radial gradients defining the flare for different morphological types and stellar mass bins. The surface brightness profiles for the faceon and edge-on views of each model were simulated to find out whether the flared disc produces a Type-II break in the disc profile when observed edge-on, and if so under what conditions. Contrary to previous claims, we find that discs with realistic flares can produce significant breaks in discs when observed edge-on. Specifically a flare with the parameters of that of the Milky Way would produce a significant break of the disc at a R_(brkII) of ∼8.6 kpc if observed edge-on. Central bulges have no significant effects on the results. These simulations show that flared discs can explain the existence of many Type-II breaks observed in edge-on galaxies, in a range of galaxies with intermediate to low break strength values of −0.25 < S < −0.1.
© 2016 ESO. The authors thank to the anonymous referee for the useful criticisms that helped to improve this publication significantly and Martín López-Corredoira for his kind support with the MW models. This research has been supported by the Ministerio de Economía y Competitividad del Gobierno de España (MINECO) under project AYA2012-31277, and by the Instituto de Astrofísica de Canarias under project P3/86. We acknowledge the usage of the HyperLeda database ( This research has made use of the NASA Astrophysics Data System and NASA/IPAC Extragalactic Database (NED) and the R environment for statistical computing.
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