Spin and structural halo properties at high redshift in a Λ cold dark matter universe

Davis, Andrew; Natarajan, Priyamvada

doi:10.1111/j.1365-2966.2010.16956.x

Cited by 14 publications

(21 citation statements)

References 88 publications

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“…There are various cuts on β used in the literature to select strictly virialized haloes: Shaw et al (2006) use β > −0.2, Bett et al (2007) use |β| < 0.5 and Neto et al (2007) use β < 0.35. As noted in Davis & Natarajan (2010), we find that our haloes do not have 〈β〉≈ 0, but are offset to high values of kinetic energy such that 〈β〉 < 0 for all redshifts, and haloes are farther from virialization at higher redshifts. One possibility is that the extra terms in the virial equation ( U ext and E s ) are not negligible at higher redshifts, where large amounts of infalling material contribute to the terms.…”

Section: Simulation Resultssupporting

confidence: 69%

“…Using gadget ‐2 (Springel 2005), we ran a dark matter only simulation with the WMAP 5 cosmological parameters ({Ω M , Ω Λ , Ω b , h , n , σ 8 } = {0.258, 0.742, 0.044, 0.719, 0.963, 0.796}, Dunkley et al 2009) from z ≈ 100 to z = 6 (see Davis & Natarajan 2010 for full details). Our dark matter particle mass m = 1.0 × 10 4 M ⊙ h −1 , which sets a comoving box size at 2.46 Mpc h −1 , with 512 3 dark matter particles.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…Press & Schechter 1974; Bond et al 1991; Sheth & Tormen 1999) also predict the halo mass function for collapsed, bound and virialized haloes in ΛCDM. However, simulations at high redshift ( z > 1) have found that the majority of collapsed, bound haloes are not in virial equilibrium (Jang‐Condell & Hernquist 2001; Hetznecker & Burkert 2006; Davis & Natarajan 2010). Thus, there seems to be a mismatch with simulations; they find mass functions (which assume the haloes are virialized) that match the analytical predictions, and yet the detailed structure of the haloes shows that they are not virialized.…”

Section: Introductionmentioning

confidence: 99%

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Virialization of high-redshift dark matter haloes

Davis

D’Aloisio

Natarajan

2011

Monthly Notices of the Royal Astronomical Society

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We present results of a study of the virial state of high-redshift dark matter haloes in an N-body simulation. We find that the majority of collapsed, bound haloes are not virialized at any redshift slice in our study (z = 15 − 6) and have excess kinetic energy. At these redshifts, merging is still rampant and the haloes cannot strictly be treated as isolated systems. To assess if this excess kinetic energy arises from the environment, we include the surface pressure term in the virial equation explicitly and relax the assumption that the density at the halo boundary is zero. Upon inclusion of the surface term, we find that the haloes are much closer to virialization; however, they still have some excess kinetic energy. We report trends of the virial ratio including the extra surface term with three key halo properties: spin, environment and concentration. We find that haloes with closer neighbours depart more from virialization and that haloes with larger spin parameters do as well. We conclude that except at the lowest masses (M < 10 6 M ), dark matter haloes at high redshift are not fully virialized. This finding has interesting implications for galaxy formation at these high redshifts, as the excess kinetic energy will impact the subsequent collapse of baryons and the formation of the first discs and/or baryonic structures.

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Section: Simulation Resultssupporting

confidence: 69%

Section: Simulation Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Virialization of high-redshift dark matter haloes

Davis

D’Aloisio

Natarajan

2011

Monthly Notices of the Royal Astronomical Society

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“…Recently, it has been reported that high spin halos are more clustered than low spin halos Davis & Natarajan 2010). Macciò et al (2007) on the other hand do not find any environmental dependence.…”

Section: Introductionmentioning

confidence: 95%

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

Sharma

Steinmetz

Bland-Hawthorn

2012

ApJ

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We perform a set of non-radiative hydrodynamical simulations of merging spherical halos in order to understand the angular momentum (AM) properties of the galactic halos seen in cosmological simulations. The universal shape of AM distributions seen in simulations is found to be generically produced as a result of mergers. The universal shape is such that it has an excess of low AM material and hence cannot explain the exponential structure of disk galaxies. A resolution to this is suggested by the spatial distribution of low AM material which is found to be in the center and a conical region close to the axis of rotation. A mechanism that preferentially discards the material in the center and prevents the material along the poles from falling onto the disk is proposed as a solution. We implement a simple geometric criterion for the selective removal of low AM material and show that in order for 90% of halos to host exponential disks one has to reject at least 40% of material. Next, we explore the physical mechanisms responsible for distributing the AM within the halo during a merger. For dark matter there is an inside-out transfer of AM, whereas for gas there is an outside-in transfer, which is due to differences between collisionless and gas dynamics. This is responsible for the spin parameter λ and the shape parameter α of AM distributions being higher for gas compared to dark matter. We also explain the apparent high spin of dark matter halos undergoing mergers and show that a criterion stricter than what is currently used would be required to detect such unrelaxed halos. Finally, we demonstrate that the misalignment of AM between gas and dark matter only occurs when the intrinsic spins of the merging halos are not aligned with the orbital AM of the system. The self-misalignment (orientation of AM when measured in radial shells not being constant), which could be the cause of warps and anomalous rotation in disks galaxies, also occurs under similar conditions. The frequency and amplitude of this misalignment are roughly consistent with the properties of warps seen in disk galaxies.

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“…One major problem lies in their choice of initial conditions, specifically in their use of solid-body rotation. Although the total angular momentum of the gas and dark matter in their simulations is comparable that measured for minihalos in more realistic cosmological simulations (Jang-Condell & Hernquist, 2001;Davis & Natarajan, 2010), their adoption of solid-body rotation leads to the gas having an incorrect radial profile for this angular momentum. This causes the collapse of the gas to be considerably more ordered than it would be in a real minihalo, leading to the formation of an over-large disk.…”

Section: Early Studiesmentioning

confidence: 93%

The First Stars

Glover

2012

The First Galaxies

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The first stars to form in the Universe -the so-called Population III stars -bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.

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Spin and structural halo properties at high redshift in a Λ cold dark matter universe

Cited by 14 publications

References 88 publications

Virialization of high-redshift dark matter haloes

Virialization of high-redshift dark matter haloes

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

The First Stars

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