arXiv subjects

T. S. Kolatt

Publications and source records attributed to T. S. Kolatt.

3 recordsLinked to original sources

arXiv2000

Spin Profile of Galactic Halos and Disk Formation

We summarize recent developments in the study of the origin of halo spin profiles and preliminary implications on disk formation. The specific angular-momentum distributions within halos in N-body simulations match a universal shape, M(<j) \propto j/(j_0+j). It is characterized by a power law over most of the mass, and one shape parameter in addition to the spin parameter λ. The angular momentum tends to be aligned throughout the halo and of cylindrical symmetry. Even if angular momentum is conserved during baryonic infall, the resultant disk density profile is predicted to deviate from exponential, with a denser core and an extended tail. A slightly corrected version of the scaling relation due to linear tidal-torque theory is used to explain the origin of a typical power-law profile in shells, j(M) \propto M^s with s \gsim 1. While linear theory crudely predicts the amplitudes of halo spins, it is not a good predictor of their directions. Independently, mergers of halos are found to produce a similar profile due to j transfer from the orbit to the product halo via dynamical friction and tidal stripping. The halo spin is correlated with having a recent major merger, though this correlation is weakened by mass loss. These two effects are due to a correlation between the spins of neighboring halos and their orbit, leading to prograde mergers.

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arXiv1999

Galaxy Interactions and Starbursts at High Redshift

Using high resolution N-body simulations with hydrodynamics and star formation, we investigate interactions and the resulting starbursts in galaxies with properties typical of $z\sim 3$. We apply spectral population models to produce mock-HST images, and discuss the observed magnitude, color, and morphological appearance of our simulated galaxies in both the rest-UV and rest-visual bands.

astro-ph↗

arXiv1996

Proper Motions Of VLBI Lenses, Inertial Frames and The Evolution of Peculiar Velocities

Precise determinations of the image positions in quad gravitational lenses using VLBI can be used to measure the transverse velocity of the lens galaxy and the observer. The typical proper motions are $μ$as yr$^{-1}$, so the time scale to measure the motion is ten years. By measuring the dipole of the proper motions in an ensemble of lenses we can set limits on the deviation of the inertial frame defined by the lenses from that defined by the CMB dipole and estimate the Hubble constant. The residual proper motions after subtracting the dipole probe the evolution of peculiar velocities with redshift and can be used to estimate the density parameter $Ω_0$. For $N$ lenses, VLBI measurement accuracies of $σ_θ$, and a baseline of $T$ years, we estimate that the 2$σ$ limit on the rms peculiar velocity of the lens galaxies is $3100 (σ_θ/10μ\{as})({yrs}/T)/N^{1/2} \kms$, and that the time required for the 2--$σ$ limit to reach the level of the local rms peculiar velocity $v_{0,rms}$ is approximately $10 N^{-1/2} (v_{0,rms}/600\kms)(σ_θ/10μas)$ years. For a ten year baseline and $N=10$ lenses we expect the 1$σ$ limit on the misalignment with the CMB dipole to be $Δθ=20^{\circ}$ or equivalently to obtain an upper limit of $ΔH_0 /H_0 < 0.34 $.

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