The Causes of Halo Shape Changes Induced by Cooling Baryons: Disks versus Substructures

By V. Debattista, B. Moore, Thomas R. Quinn, S. Kazantzidis, R. Maas, Lucio Mayer, Justin I. Read, Joachim Stadel. 2007

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Cold dark matter cosmogony predicts triaxial dark matter halos, whereas observations find quite round halos. This is most likely due to the condensation of baryons leading to rounder halos. We examine the halo phase space distribution basis for such shape changes. Triaxial halos are supported by box orbits, which pass arbitrarily close to the density center. The decrease in triaxiality caused by baryons is thought to be due to the scattering of these orbits. We test this hypothesis with simulations of disks grown inside triaxial halos. After the disks are grown we check whether the phase space structure has changed by evaporating the disks and comparing the initial and final states. While the halos are substantially rounder when the disk is at full mass, their final shape after the disk is evaporated is not much different from the initial. Likewise, the halo becomes (more) radially anisotropic when the disk is grown, but the final anisotropy is consistent with the initial. Only if the baryons are unreasonably compact or massive does the halo change irreversibly. We show that the character of individual orbits is not generally changed by the growing mass. Thus, the central condensation of baryons does not destroy enough box orbits to cause the shape change. Rather, box orbits merely become rounder along with the global potential. However, if angular momentum is transferred to the halo, either via satellites or via bars, a large irreversible change in the halo distribution occurs. The ability of satellites to alter the phase space distribution of the halo is of particular concern to galaxy formation simulations since halo triaxiality can profoundly influence the evolution of disks.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7728fa438fca432019d2a631dbb17fc19d46992f

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Citations in the corpus

Formation of Galaxy Clusters (2012, background): “The main mechanism behind this effect lies in adiabatic changes of the shapes of particle orbits in response to more centrally concentrated mass distribution after baryon dissipation (Debattista et al. 2008, Dubinski1994).”
Impact of baryon physics on dark matter structures: a detailed simulation study of halo density profiles (2010, methodology): “With the addition of baryons to the simulation, one can expect further effects due to the transfer of angular momentum from infalling satellites (e.g. Debattista et al. 2008; Romano-Dı́az et al. 2008).”
THE SHAPE OF THE INNER MILKY WAY HALO FROM OBSERVATIONS OF THE PAL 5 AND GD–1 STELLAR STREAMS (2016, background): “…of a galactic baryonic disk causes the halos to become more axisymmetric and aligned with the disk, but the minor-to-major axis ratio c/a changes only by a few tenths to c/a ≈ 0.7 to 0.8 (Dubinski 1994; Gustafsson et al. 2006; Debattista et al. 2008; Abadi et al. 2010; Kazantzidis et al. 2010).”
Dark matter response to galaxy formation (2009, background): “However, their shape changes, becoming more nearly oblate as baryons condense within them (Katz & Gunn 1991; Evrard et al. 1994; Tissera & Domı́nguez-Teneiro 1998; Kazantzidis et al 2004; Debattista et al. 2008; A09).”
Two-dimensional kinematics of SLACS lenses – III. Mass structure and dynamics of early-type lens galaxies beyond z ≃ 0.1 (2011, result): “Such a scenario appears to be in general agreement with the results of numerical simulations (e.g. Debattista et al. 2008; Abadi et al. 2010), which show that the assembly of massive high angular momentum galaxies changes the dark halo into nearlyaxially symmetric, slightly oblate systems over a…”
THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, background): “If a disk were to form in an elliptical halo potential such as that proposed in §4.3, simulations suggest that the disk too should become elongated and non-axisymmetric (see, e.g., Gerhard & Vietri 1986; Debattista et al. 2008).”
The shape of dark matter haloes in the Aquarius simulations: evolution and memory (2011, background): “It is important to stress that we have neglected the effects induced by the presence of baryons on the dark matter halo shapes (Kazantzidis et al. 2004; Bailin et al. 2005; Gustafsson et al. 2006; Debattista et al. 2008; Pedrosa et al. 2009; Lau et al. 2011; Valluri et al. 2010).”
Colloquium: Annual modulation of dark matter (2013, background): “…cooling changes halo shapes from prolate triaxial to more spherical when baryons are added (Dubinski and Carlberg, 1991; Kazantzidis et al., 2004; Debattista et al., 2008; Valluri et al., 2009; Zemp et al., 2012), with velocity distributions that are expected to deviate less from the standard…”
The mass distribution and gravitational potential of the Milky Way (2016, background): “It is recognised that, again, baryonic physics will play an important role – condensationof baryons to the centres of haloes is expected to make them rounder than dark-matter-only simulations would suggest (Debattista et al. 2008).”
Cosmological simulations with self-interacting dark matter – II. Halo shapes versus observations (2012, background): “In particular, simulations of isolated disky galaxies indicate that the presence of baryons tends to make the dark-matter distribution more spherical, although it is not clear how much the dark-matter distribution changes if the central galaxy is elliptical instead (Debattista et al. 2008).”
Bar formation and evolution in disc galaxies with gas and a triaxial halo: morphology, bar strength and halo properties (2012, background): “…several papers (Dubinski 1994; Gadotti & de Souza 2003; Berentzen & Shlosman 2006; Berentzen, Shlosman & Jogee 2006; Curir, Mazzei & Murante 2006; Athanassoula 2007; Debattista et al. 2008; Widrow 2008; Machado & Athanassoula 2010, hereafter MA10), but a full understanding is still not available.”
Co-formation of the disc and the stellar halo (2018, background): “According to Debattista et al. (2008), halo contraction due to baryonic condensation may make the DM halos slightly more radially anisotropic, but overall, the changes are small and the β trends with Galacto-centric distance are preserved.”
Mass models of the Milky Way (2011, background): “It is recognised that, again, baryonic physics will play an important role – condensation of baryons to the centres of haloes is expected to make them rounder than dark-matter-only simulations would suggest (Debattista et al. 2008).”
Misaligned angular momentum in hydrodynamic cosmological simulations: warps, outer discs and thick discs (2010, methodology): “This procedure is analogous to that used in Katz (1991), though it uses differential instead of cumulative shells following Debattista et al. (2008).”
THE TWO PHASES OF GALAXY FORMATION (2010, background): “…expected from the effect of adiabatic contraction galaxies with significant in-situ star formation, i.e. more dissipation, live in more concentrated halos (Blumenthal et al. 1986; Dubinski 1994; Jesseit et al. 2002; Debattista et al. 2008; Gnedin et al. 2004; Abadi et al. 2010; Auger et al. 2010).”