The kinematics of local thick discs do not support an accretion origin
|Author:||Comerón, S.1; Salo, H.1; Knapen, J. H.2,2,3;|
1University of Oulu, Astronomy Research Unit, PO Box 3000, 90014 Oulu, Finland
2Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
3Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
4Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
|Online Access:||PDF Full Text (PDF, 2.2 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe2019040911642
|Publish Date:|| 2019-04-09
Thick discs are nearly ubiquitous components of the discs of present-day galaxies. It has been proposed that a fraction of their stars have been accreted. Here, we aim to find whether accretion of satellites is the main formation mechanism of thick discs. To do so, we observed a sample of eight nearby edge-on galaxies with the Multi-Unit Spectroscopic Explorer (MUSE) integral field unit at the Very Large Telescope (VLT). Six of the galaxies have a distinct thick disc. We derived thick-disc velocities and velocity dispersions for the galaxies in our sample. We devise a formalism to estimate the fractions of retrograde material in the thick discs by using kinematical maps and thin/thick disc decompositions. None of the galaxies in our sample show strong evidence for retrograde material at large distances from the centre. Including those found in the literature, there are seventeen thick discs with studied kinematics, with only one showing unambiguous signatures of retrograde material. Literature numerical studies of dynamical friction allow us to estimate that at the current cosmic time about one in six mergers for which the stars of the accreted galaxy ended in a thick disc were retrograde. This is in tension with the observed fraction of galaxies with a partly retrograde thick disc (one in seventeen). We conclude that satellite accretion is not favoured by observations to be the main formation mechanism of thick discs.
Astronomy and astrophysics
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
115 Astronomy and space science
SC and HS acknowledge support from the Academy of Finland (grant No. 297738). HS, JHK, and RFP acknowledge financial support from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 721463 to the SUNDIAL ITN network. JHK acknowledges additional support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-76219-P, as well as from the Fundación BBVA under its 2017 programme of assistance to scientific research groups, for the project “Using machine-learning techniques to drag galaxies from the noise in deep imaging”, and from the Leverhulme Trust through the award of a Visiting Professorship at LJMU.
|EU Grant Number:||
(721463) SUNDIAL - SUrvey Network for Deep Imaging Analysis and Learning
|Academy of Finland Grant Number:||
297738 (Academy of Finland Funding decision)
© ESO 2019.