Making counter-orbiting tidal debris

Abstract

Using stellar-dynamical calculations it is shown for the first time that counter-orbiting material emerges naturally in tidal interactions of disc galaxies. Model particles on both pro-and retrograde orbits can be formed as tidal debris in single encounters with disc galaxies of 1-to-1 and 4-to-1 mass ratios. A total of 74 model calculations are performed for a range of different initial parameters. Interactions include fly-by and merger cases. The fraction of counter-orbiting material produced varies over a wide range (from a few up to 50 percent). All fly-by models show a similar two-phase behaviour, with retrograde material forming first. Properties of the prograde and retrograde populations are extracted to make an observational discrimination possible. During such encounters the tidal debris occupies a certain region in phase space. In this material, tidal-dwarf galaxies may form. The modelling therefore can explain why galaxies may have dwarf galaxies orbiting counter to the bulk of their dwarf galaxies. An example is the Sculptor dwarf of the Milky Way, which orbits counter to the bulk of the disc of satellites. The modelling thus supports the scenario of the MW satellites being ancient tidal-dwarf galaxies formed from gaseous material stripped from another galaxy during an encounter with the young MW. A possible candidate for this galaxy is identified as the Magellanic Cloud progenitor galaxy. Its angular motion fits the angular motion of the MW disc of satellites objects. This scenario is in agreement with Lynden-Bell's original suggestion for the origin of the dSph satellites and the near-unbound orbit of the LMC.

The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology

“…Documented for the first time by Pawlowski et al (2011) is the natural emergence of counter-rotating tidal material in excellent agreement with the counter-orbiting Sculptor dSph satellite. These models show how the ratio of pro-and counter-rotating tidal debris about the MW significantly constrains the allowed encounter.…”

Space Motions of the Dwarf Spheroidal Galaxies Draco and Sculptor Based on HST Proper Motions with a ∼10 yr Time Baseline

“…Cosmological simulations show that in such a scenario the orbital angular momenta of all group members should be well aligned (Sales et al 2011). This analysis, however, does not rule out that Draco and Sculptor were accreted as part of a loose group or tidal structures that were split apart upon infall (e.g., Pawlowski et al 2011). …”

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

“…Given that dSphs are preferentially located near the massive spirals Milky Way (MW) and M31, various environmental mechanisms have been invoked to explain their origin (e.g., Einasto et al 1974;Faber & Lin 1983;Kroupa 1997;Mayer et al 2001aMayer et al , 2001bMayer et al , 2006Mayer et al , 2007Kravtsov et al 2004;D'Onghia et al 2009;Klimentowski et al 2009;Kazantzidis et al 2011Kazantzidis et al , 2013Pawlowski et al 2011;Yozin & Bekki 2012). 6 In this context, the "tidal stirring" model (Mayer et al 2001b) posits that gravitational and hydrodynamical interactions with MWsized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregulars (dIrrs), into systems with the kinematic and structural properties of dSphs.…”