The shape of dark matter haloes in the Aquarius simulations: evolution and memory

Vera-Ciro, Carlos; Sales, Laura V.; Helmi, Amina; Frenk, Carlos S.; Navarro, Julio F.; Springel, Volker; Vogelsberger, Mark; White, Simon D. M.

doi:10.1111/j.1365-2966.2011.19134.x

Cited by 169 publications

(216 citation statements)

References 113 publications

(154 reference statements)

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“…This supports the idea that the DM elongation at high redshifts, soon after the assembly, is induced by the preferred direction of the large-scale structure. This is compatible with the results of Vera-Ciro et al (2011), who showed using DM-only simulations that at high redshift, when haloes are fed through narrow filaments, prolateness dominates. The shape of the haloes changes to a more oblate configuration at lower redshift, when the accretion becomes more isotropic.…”

Section: Origin Of Halo Elongationsupporting

confidence: 92%

Evolution of galaxy shapes from prolate to oblate through compaction events

Tomassetti

Dekel²,

Mandelker³

et al. 2016

Mon. Not. R. Astron. Soc.

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We study the evolution of global shapes of galaxies using cosmological simulations. The shapes refer to the components of dark matter (DM), stars and gas at the stellar half-mass radius. Most galaxies undergo a characteristic compaction event into a blue nugget at z ∼ 2 − 4, which marks the transition from a DM-dominated central body to a self-gravitating baryonic core. We find that in the high-z, DM-dominated phase, the stellar and DM systems tend to be triaxial, preferentially prolate and mutually aligned. The elongation is supported by an anisotropic velocity dispersion that originates from the assembly of the galaxy along a dominant large-scale filament. We estimate that torques by the dominant halo are capable of inducing the elongation of the stellar system and its alignment with the halo. Then, in association with the transition to self-gravity, small-pericenter orbits puff up and the DM and stellar systems evolve into a more spherical and oblate configuration, aligned with the gas disc and associated with rotation. This transition typically occurs when the stellar mass is ∼ 10 9 M and the escape velocity in the core is ∼ 100 km s −1 , indicating that supernova feedback may be effective in keeping the core DM-dominated and the system prolate. The early elongated phase itself may be responsible for the compaction event, and the transition to the oblate phase may be associated with the subsequent quenching in the core.

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Section: Origin Of Halo Elongationsupporting

confidence: 92%

Evolution of galaxy shapes from prolate to oblate through compaction events

Tomassetti

Dekel²,

Mandelker³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The shape of the halo is unknown, but is here assumed to be spherical. There have been studies showing that the dark-matter halo might be highly oblate or prolate (e.g., Amorisco & Bertin 2010;Vera-Ciro et al 2011). This would further increase σ z .…”

Section: Uncertainties and Assumptionsmentioning

confidence: 99%

The DiskMass Survey

Martinsson

Verheijen

Westfall

et al. 2013

A&A

197

225

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We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities (Σ dyn ). By subtracting our observed atomic and inferred molecular gas mass surface densities from Σ dyn , we derived the stellar mass surface densities (Σ * ), and thus have absolute measurements of all dominant baryonic components of the galaxies. Using K-band surface brightness profiles (I K ), we calculated the K-band mass-to-light ratio of the stellar disks (Υ * = Σ * /I K ) and adopted the radial mean (Υ * ) for each galaxy to extrapolate Σ * beyond the outermost kinematic measurement. The derived Υ * of individual galaxies are consistent with all galaxies in the sample having equal Υ * . We find a sample average and scatter of Υ * = 0.31 ± 0.07. Rotation curves of the baryonic components were calculated from their deprojected mass surface densities. These were used with circular-speed measurements to derive the structural parameters of the dark-matter halos, modeled as either a pseudo-isothermal sphere (pISO) or a Navarro-Frenk-White (NFW) halo. In addition to our dynamically determined mass decompositions, we also performed alternative rotation-curve decompositions by adopting the traditional maximumdisk hypothesis. However, the galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (h R ) the ratios between the baryonic and total rotation curves (F 2.2h R b ) are less than 0.75. We find this ratio to be nearly constant between 1-6h R within individual galaxies. We find a sample average and scatter of F 2.2h R b = 0.57 ± 0.07, with trends of larger F 2.2h R b for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale Υ * by a factor 3.6 on average. In general, the dark-matter rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-Υ * (submaximal) case, we find that the derived NFW-halo parameters have values consistent with ΛCDM N-body simulations, suggesting that the baryonic matter in our sample of galaxies has only had a minor effect on the dark-matter distribution. In contrast, maximum-Υ * decompositions yield halo-concentration parameters that are too low compared to the ΛCDM simulations.

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“…After this time, material was fed into the halo of Aq-D mainly via a secondary filament, oriented nearly perpendicular to the primary filament that dominates the local large-scale structure. Vera-Ciro et al (2011) find that the dark matter halo of Aq-D changes its orientation owing to the change in infall direction. This change in infall direction is likely the main reason why no rotation signal is detected in the mock GC systems around this halo.…”

Section: Aq-dmentioning

confidence: 83%

“…To understand the reason behind this, we need to consider the assembly history of the structure around Aq-D. Vera-Ciro et al (2011) studied in detail the evolution of the dark matter halo surrounding the Aquarius galaxies. In the case of Aq-D, they found that until redshift of z ≈ 0.75, most of the material infall occurred along the primary filament this halo was situated on.…”

Section: Aq-dmentioning

confidence: 99%

The kinematics of globular clusters systems in the outer halos of the Aquarius simulations

Veljanoski

Helmi

2016

A&A

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Stellar halos and globular cluster (GC) systems contain valuable information regarding the assembly history of their host galaxies. Motivated by the detection of a significant rotation signal in the outer halo GC system of M 31, we investigate the likelihood of detecting such a rotation signal in projection, using cosmological simulations. To this end we select subsets of tagged particles in the halos of the Aquarius simulations to represent mock GC systems, and analyse their kinematics. We find that GC systems can exhibit a non-negligible rotation signal provided the associated stellar halo also has a net angular momentum. The ability to detect this rotation signal is highly dependent on the viewing perspective, and the probability of seeing a signal larger than that measured in M 31 ranges from 10% to 90% for the different halos in the Aquarius suite. High values are found from a perspective such that the projected angular momentum of the GC system is within 40 deg of the rotation axis determined via the projected positions and line-of-sight velocities of the GCs. Furthermore, the true 3D angular momentum of the outer stellar halo is relatively well aligned, within 35 deg, with that of the mock GC systems. We argue that the net angular momentum in the mock GC systems arises naturally when the majority of the material is accreted from a preferred direction, namely along the dominant dark matter filament of the large-scale structure that the halos are embedded in. This, together with the favourable edge-on view of M 31's disk suggests that it is not a coincidence that a large rotation signal has been measured for its outer halo GC system.

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The shape of dark matter haloes in the Aquarius simulations: evolution and memory

Cited by 169 publications

References 113 publications

Evolution of galaxy shapes from prolate to oblate through compaction events

Evolution of galaxy shapes from prolate to oblate through compaction events

The DiskMass Survey

The kinematics of globular clusters systems in the outer halos of the Aquarius simulations

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