The reports of thick discs' death are greatly exaggerated: Thick discs are NOT artefacts caused by diffuse scattered light

Dr. Sébastien Comerón
See the live streaming of this talk on Thursday August 24, 10:30 GMT (GMT+1 Summer time).

Abstract

The reports of thick discs' death are greatly exaggerated: Thick discs are NOT artefacts caused by diffuse scattered light

Recent studies have made the community aware of the importance of accounting for scattered light when examining low surface brightness galaxy features such as thick discs. In past studies on thick discs of edge-on galaxies the point spread function (PSF) effects were not taken into account or were modelled with a Gaussian kernel.

We have re-examined results on photometric decompositions of discs in the Spitzer Survey of Stellar Structure of Galaxies (S4G) using a revised PSF model that accounts for extended wings out to more than 2.5 arcminutes. We study 141 edge-on galaxies, so we more than double the samples examined in past studies. This is the largest sample of extragalactic thick discs studied so far.

The main difference between our current fits and those presented in the past is that now the scattered light from the thin disc dominates the surface brightness at levels below 26 mag arcsec-2. This change, however, does not affect drastically any of our previously presented results: 

- Thick discs are nearly ubiquitous. They are not an artefact caused by scattered light as has been suggested elsewhere. 
- Thick discs have masses comparable to those of thin discs in low-mass galaxies (with circular velocities v_c<120 km s-2) whereas they are typically less massive than the thin discs in high-mass galaxies.
- Thick discs and central mass concentrations seem to have formed at the same epoch from a common material reservoir.
- Approximately sixty per cent of the up-bending breaks in face-on galaxies are caused by the superposition of a thin and a thick disc where the scale-length of the latter is the largest.

About the talk

The reports of thick discs' death are greatly exaggerated: Thick discs are NOT artefacts caused by diffuse scattered light
Dr. Sébastien Comerón
University of Oulu, Finland
Thursday August 24, 2017
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