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

TL;DR

This study demonstrates that realistic disc flares in edge-on galaxies can produce Type-II surface brightness profile breaks, challenging previous assumptions and explaining observed features across various galaxy types.

Contribution

It provides a systematic analysis using realistic models showing that disc flares can cause Type-II breaks in edge-on galaxy profiles, which was previously underestimated.

Findings

Flares with Milky Way parameters produce significant breaks at ~8.6 kpc.

Realistic bulge properties do not significantly affect the results.

Flares can explain many observed Type-II breaks in edge-on galaxies.

Abstract

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, analyzed this hypothesis systematically using realistic models for the disc, the flare, and the bulge. We revisit this theme by analyzing a series of models which sample a wide range of observationally based structural parameters for these three components. 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, based on observations. The surface brightness profiles for the face-on 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 Rbreak 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 low-to-intermediate break strength values of -0.25<S<-0.1.