Radial migration does little for Galactic disc thickening

By I. Minchev, B. Famaey, A. Quillen, W. Dehnen, M. Martig, A. Siebert. 2012

141 citations recorded by the source corpus.

Non-axisymmetric components, such as spirals and central bars, play a major role in shaping galactic discs. An important aspect of the disc secular evolution driven by these perturbers is the radial migration of stars. It has been suggested recently that migration can populate a thick-disc component from inner-disc stars with high vertical energies. Since this has never been demonstrated in simulations, we study in detail the effect of radial migration on the disc velocity dispersion and disc thickness, by separating simulated stars into migrators and non-migrators. We apply this method to three isolated barred Tree-SPH N-body galaxies with strong radial migration. Contrary to expectations, we find that as stellar samples migrate, on the average, their velocity dispersion change (by as much as 50%) in such a way as to approximately match the non-migrating population at the radius at which they arrive. We show that, in fact, migrators suppress heating in parts of the disc. To confirm the validity of our findings, we also apply our technique to three cosmological re-simulations, which use a completely different simulation scheme and, remarkably, find very similar results. We believe the inability of migration to thicken discs is a fundamental property of internal disc evolution, irrespective of the migration mechanism at work. We explain this with the approximate conservation of the (average) vertical and radial actions rather than the energy. This “action mixing” can be used to constrain the migration rate in the Milky Way: estimates of the average vertical action in observations for different populations of stars should reveal flattening with radius for older groups of stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e8b1e8637b1e5b95e5854d915d7d022dd0c42736

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Citations in the corpus

THE STELLAR POPULATION STRUCTURE OF THE GALACTIC DISK (2015, background): “…that may have occurred in the MW, current simulations do indicate that kinematic biases in the population of migrators are significant enough that little or no effect on the vertical structure of the disk should be expected (Minchev et al. 2012; Roškar et al. 2013; Vera-Ciro et al. 2014).”
The effects of radial migration on the vertical structure of Galactic discs (2012, methodology): “This is similar tothe model described by Minchev et al. (2012a), who use it to show tat the vertical velocity dispersion is expected to decrease asstar migrate outward if the vertical action is conserved.”
The Milky Way’s stellar disk (2013, methodology): “…radial migration appears to conserve approximately the vertical action (not the vertical energy, cf. Schönrich & Binney (2009)), which will slightly thicken the disk portions that have migrated outward and slightly decrease their vertical velocity (Solway et al. 2012; Minchev et al. 2012a).”
7Li evolution in the thin and thick discs of the Milky Way (2018, background): “This idea was challenged by Minchev et al. (2012), demonstrating that migrators in N-body models do not have any significant effect on disk thickening.”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, background): “Kinematical heating and spatial disruption can be produced via several process, such as bar resonances and radial mixing, clumpiness in the gas caused, and minor mergers, to name a few (e.g. Minchev et al. 2012; Rix & Bovy 2013; Haywood et al. 2013; Sanders & Binney 2013, 2015).”
TRACING CHEMICAL EVOLUTION OVER THE EXTENT OF THE MILKY WAY'S DISK WITH APOGEE RED CLUMP STARS (2014, background): “…that this mechanism is able to produce a thick-disk component in agreement with many local observations, although more realistic simulations cast serious doubt on whether radial migration can produce enough (Roškar et al. 2013) or even any (Minchev et al. 2012b; Vera-Ciro et al. 2014b) heating.”
Constraining the Milky Way assembly history with Galactic Archaeology (2016, methodology): “The full description and simulation setup can be found in Minchev et al. (2012b).”
CHEMICAL CARTOGRAPHY WITH APOGEE: LARGE-SCALE MEAN METALLICITY MAPS OF THE MILKY WAY DISK (2013, background): “Whether radial mixing can heat stars enough to result in a thickdisk population with the vertical scale height of the Milky Way’s thick disk is the subject of much theoretical dispute (e.g., Minchev et al. 2012).”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “…been discussed in the literature A109, page 14 of 18 (Sellwood & Binney 2002; Schönrich & Binney 2009a; Roškar et al. 2008; Minchev & Famaey 2010; Minchev et al. 2011, 2012a,b; Di Matteo et al. 2013) is the result of a secular process related to the presence of stellar asymmetries likes bars and…”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, result): “This looks contradictory to our results and Minchev et al. (2012) who showed that the particles which migrate outwards are vertically hotter than the particles at their new radii.”
THE EFFECT OF RADIAL MIGRATION ON GALACTIC DISKS (2014, background): “Minchev et al. (2012b), on the other hand, have argued that migration does little for disk thickening because outward migrators should cool vertically as they move out, a result that has been further debated by Solway et al. (2012) and Roškar et al. (2013).”
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient (2018, background): “This origin coincides with the end of the Galactic bar, which is expected to produce most of the radial migration in the inner disk after its formation (e.g., Minchev et al. 2012a; Di Matteo et al. 2013).”
Dissecting simulated disc galaxies - I. The structure of mono-age populations (2014, methodology): “Some authors have also argued that radial migration could create a thick disc (Schönrich & Binney 2009a,b; Loebman et al. 2011), although Minchev et al. (2012b) recently showed that radial migration alone is not efficient at heating discs.”
Chemodynamical evolution of the Milky Way disk - I. The solar vicinity (2012, background): “(2011b) and Minchev et al. (2012b), who demonstrated that migrators are generally not expected to heat the disk becaus of the approximate conservation of the average radial and vertical actions in the absence of external perturbers.”
The GALAH survey: scientific motivation (2015, background): “…thick disc is a matter of ongoing debate (e.g. Abadi et al. 2003; Brook et al. 2005; Villalobos & Helmi 2008; Loebman et al. 2011; Bovy et al. 2012; Minchev et al. 2012), with suggestions that it was accreted, heated from the thin disc by interactions with satellite galaxies, formed in situ, built…”
Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood (2013, background): “On the other hand, if the formation of the thick disk is fast, e.g., through kinematical heating of an old disk due to an ancient merger event, it is more likely that the two disks are distinct components in chemistry and phase-space (Minchev et al. 2012).”
THE VERTICAL METALLICITY GRADIENT OF THE MILKY WAY DISK: TRANSITIONS IN [α/Fe] POPULATIONS (2014, background): “However, models of how radial migration affects Galactic structure vary significantly (e.g., Schönrich & Binney 2009a, Loebman et al. 2011, Minchev et al. 2012); in particular, assumed parameters, such as the star formation history, can drastically affect observable predictions, like the vertical…”