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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
The Dynamics Of Tidal Tails From Massive Satellites, Jh Choi, Md Weinberg, N Katz
The Dynamics Of Tidal Tails From Massive Satellites, Jh Choi, Md Weinberg, N Katz
Astronomy Department Faculty Publication Series
We investigate the dynamical mechanisms responsible for producing tidal tails from dwarf satellites using N-body simulations. We describe the essential dynamical mechanisms and morphological consequences of tail production in satellites with masses greater than 0.0001 of the host halo virial mass. We identify two important dynamical coconspirators: (1) the points where the attractive force of the host halo and satellite are balanced (X-points) do not occur at equal distances from the satellite centre or at the same equipotential value for massive satellites, breaking the morphological symmetry of the leading and trailing tails and (2) the escaped ejecta in the leading …
Dark Matter Halo Response To The Disc Growth, Jh Choi, Y Lu, Hj Mo, Md Weinberg
Dark Matter Halo Response To The Disc Growth, Jh Choi, Y Lu, Hj Mo, Md Weinberg
Astronomy Department Faculty Publication Series
We consider the sensitivity of the circular-orbit adiabatic contraction approximation to the baryon condensation rate and the orbital structure of dark matter haloes in the Λ cold dark matter (ΛCDM) paradigm. Using one-dimensional hydrodynamic simulations including the dark matter halo mass accretion history and gas cooling, we demonstrate that the adiabatic approximation is approximately valid even though haloes and discs may assemble simultaneously. We further demonstrate the validity of the simple approximation for ΛCDM haloes with isotropic velocity distributions using three-dimensional N-body simulations. This result is easily understood: an isotropic velocity distribution in a cuspy halo requires more circular orbits …
How Do Galaxies Get Their Gas?, D Keres, N Katz, Dh Weinberg, R Dave
How Do Galaxies Get Their Gas?, D Keres, N Katz, Dh Weinberg, R Dave
Astronomy Department Faculty Publication Series
We examine the temperature history of gas accreted by forming galaxies in smoothed particle hydrodynamics simulations. About half of the gas follows the track expected in the conventional picture of galaxy formation, shock heating to roughly the virial temperature of the galaxy potential well (T∼ 106 K for a Milky Way type galaxy) before cooling, condensing and forming stars. However, the other half radiates its acquired gravitational energy at much lower temperatures, typically T < 105 K, and the histogram of maximum gas temperatures is clearly bimodal. The ‘cold mode’ of gas accretion dominates for low-mass galaxies (baryonic …
Ly Alpha Flux Power Spectrum And Its Covariance, H Zhan, R Dave, D Eisenstein, N Katz
Ly Alpha Flux Power Spectrum And Its Covariance, H Zhan, R Dave, D Eisenstein, N Katz
Astronomy Department Faculty Publication Series
We analyse the flux power spectrum and its covariance using simulated Lyα forests. We find that pseudo-hydro techniques are good approximations of hydrodynamical simulations at high redshift. However, the pseudo-hydro techniques fail at low redshift because they are insufficient for characterizing some components of the low-redshift intergalactic medium, notably the warm–hot intergalactic medium. Hence, to use the low-redshift Lyα flux power spectrum to constrain cosmology, one would need realistic hydrodynamical simulations. By comparing (one-dimensional) mass statistics with flux statistics, we show that the non-linear transform between density and flux quenches the fluctuations so that the flux power spectrum is much …
Galaxy Clustering And Galaxy Bias In A Lambda Cdm Universe, Dh Weinberg, R Dave, N Katz, L Hernquist
Galaxy Clustering And Galaxy Bias In A Lambda Cdm Universe, Dh Weinberg, R Dave, N Katz, L Hernquist
Astronomy Department Faculty Publication Series
We investigate galaxy clustering and the correlations between galaxies and mass in the ΛCDM cosmological model (inflationary cold dark matter with Ωm = 0.4, ΩΛ = 0.6, h = 0.65, n = 0.95, and σ8 = 0.8), using a large, smoothed particle hydrodynamics simulation (SPH; with 2 × 1443 particles in a 50 h-1 Mpc cube). Simulated galaxies can be unambiguously identified as clumps of stars and cold gas a few kpc to a few tens of kpc across, residing in extended halos of hot gas and dark matter; the space density of the resolved …
X-Ray Absorption By The Low-Redshift Intergalactic Medium: A Numerical Study Of The Lambda Cold Dark Matter Model, Xl Chen, Dh Weinberg, N Katz, R Dave
X-Ray Absorption By The Low-Redshift Intergalactic Medium: A Numerical Study Of The Lambda Cold Dark Matter Model, Xl Chen, Dh Weinberg, N Katz, R Dave
Astronomy Department Faculty Publication Series
Using a hydrodynamic simulation of a cold dark matter universe with a cosmological constant, we investigate the "X-ray forest" absorption imprinted on the spectra of background quasars by the intervening intergalactic medium (IGM), at redshift z 0. In agreement with previous studies, we find that O VII and O VIII produce the strongest absorption features. The strong oxygen absorbers that might be detectable with Chandra or XMM-Newton arise in gas with T ~ 105.5-106.5 K and overdensities δ 100 that are characteristic of galaxy groups. Future X-ray missions could detect weaker oxygen absorption produced by gas with …
The Influence Of Omega(B) On High-Redshift Structure, Jp Gardner, N Katz, L Hernquist, Dh Weinberg
The Influence Of Omega(B) On High-Redshift Structure, Jp Gardner, N Katz, L Hernquist, Dh Weinberg
Astronomy Department Faculty Publication Series
We analyze high-redshift structure in three hydrodynamic simulations that have identical initial conditions and cosmological parameters and differ only in the value of the baryon density parameter, Ωb = 0.02, 0.05, and 0.125. Increasing Ωb does not change the fraction of baryons in the diffuse (unshocked) phase of the intergalactic medium, but it increases cooling rates and therefore transfers some baryons from the shocked intergalactic phase to the condensed phase associated with galaxies. Predictions of Lyα forest absorption are almost unaffected by changes in Ωb at velocity scales greater than 5 km s-1 (our resolution limit), …
X-Ray Scaling Relations Of Galaxy Groups In A Hydrodynamic Cosmological Simulation, R Dave, N Katz, Dh Weinberg
X-Ray Scaling Relations Of Galaxy Groups In A Hydrodynamic Cosmological Simulation, R Dave, N Katz, Dh Weinberg
Astronomy Department Faculty Publication Series
We examine the scalings of X-ray luminosity, temperature, and dark matter or galaxy velocity dispersion for galaxy groups in a ΛCDM cosmological simulation, which incorporates gravity, gas dynamics, radiative cooling, and star formation, but no substantial nongravitational heating. In agreement with observations, the simulated LX-σ and LX-TX relations are steeper than those predicted by adiabatic simulations or self-similar models, with LX σ4.4 and LX T for massive groups and significantly steeper relations below a break at σ 180 km s-1 (TX 0.7 keV). The TX-σ relation …
Baryons In The Warm-Hot Intergalactic Medium, R Dave, R Cen, Jp Ostriker, Gl Bryan, L Hernquist, N Katz, Dh Weinberg, Ml Norman, B O'Shea
Baryons In The Warm-Hot Intergalactic Medium, R Dave, R Cen, Jp Ostriker, Gl Bryan, L Hernquist, N Katz, Dh Weinberg, Ml Norman, B O'Shea
Astronomy Department Faculty Publication Series
Approximately 30%-40% of all baryons in the present-day universe reside in a warm-hot intergalactic medium (WHIM), with temperatures in the range 105 < T < 107 K. This is a generic prediction from six hydrodynamic simulations of currently favored structure formation models having a wide variety of numerical methods, input physics, volumes, and spatial resolutions. Most of these warm-hot baryons reside in diffuse large-scale structures with a median overdensity around 10-30, not in virialized objects such as galaxy groups or galactic halos. The evolution of the WHIM is primarily driven by shock heating from gravitational perturbations breaking on mildly nonlinear, nonequilibrium …
The Effects Of Gasdynamics, Cooling, Star Formation, And Numerical Resolution In Simulations Of Cluster Formation, Gf Lewis, A Babul, N Katz, T Quinn, L Hernquist, Dh Weinberg
The Effects Of Gasdynamics, Cooling, Star Formation, And Numerical Resolution In Simulations Of Cluster Formation, Gf Lewis, A Babul, N Katz, T Quinn, L Hernquist, Dh Weinberg
Astronomy Department Faculty Publication Series
We present the analysis of a suite of simulations of a Virgo-mass galaxy cluster. Undertaken within the framework of standard cold dark matter cosmology, these simulations were performed at differing resolutions and with increasingly complex physical processes, with the goal of identifying the effects of each on the evolution of the cluster. We focus on the cluster at the present epoch and examine properties including the radial distributions of density, temperature, entropy, and velocity. We also map "observable" projected properties such as the surface mass density, X-ray surface brightness, and Sunyaev-Zeldovich signature. We identify significant differences between the simulations, which …
An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg
An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg
Astronomy Department Faculty Publication Series
An expansion of a density field or particle distribution in basis functions that solve the Poisson equation both provides an easily parallelized N-body force algorithm and simplifies perturbation theories. The expansion converges quickly and provides the highest computational advantage if the lowest order potential-density pair in the basis looks like the unperturbed galaxy or stellar system. Unfortunately, there are only a handful of such bases in the literature that limit this advantage. This paper presents an algorithm for deriving these bases to match a wide variety of galaxy models. The method is based on efficient numerical solution of the Sturm-Liouville …
Fluctuations In Finite-N Equilibrium Stellar Systems, Md Weinberg
Fluctuations In Finite-N Equilibrium Stellar Systems, Md Weinberg
Astronomy Department Faculty Publication Series
Gravitational amplification of Poisson noise in stellar systems is important on large scales. For example, it increases the dipole noise power by roughly a factor of 6 and the quadrupole noise by 50 per cent for a King model profile. The dipole noise is amplified by a factor of 15 for the core-free Hernquist model. The predictions are computed by summing over the wakes caused by each star in the system — the dressed-particle formalism of Rostoker & Rosenbluth — and are demonstrated by N-body simulation. This result implies that a collisionless N-body simulation is impossible; the fluctuation noise which …
Constraining The Metallicity Of The Low-Density Ly Alpha Forest Using O Vi Absorption, R Dave, U Hellsten, L Hernquist, N Katz, Dh Weinberg
Constraining The Metallicity Of The Low-Density Ly Alpha Forest Using O Vi Absorption, R Dave, U Hellsten, L Hernquist, N Katz, Dh Weinberg
Astronomy Department Faculty Publication Series
We present a systematic search for O VI (1032, 1037 Å) absorption in a Keck High-Resolution Echelle Spectrometer spectrum of the z = 3.62 quasar Q1422+231, with the goal of constraining the metallicity and ionization state of the low-density intergalactic medium (IGM). Comparison of C IV absorption measurements to models of the Lyα forest based on cosmological simulations shows that absorbers with NH I 1014.5 cm-2 have a mean carbon abundance [C/H] -2.5, assuming a metagalactic photoionizing background with the spectral shape predicted by Haardt and Madau in 1996. In these models, lower column density absorption arises …
Cosmological Simulations With Scale-Free Initial Conditions. I. Adiabatic Hydrodynamics, Jm Owen, Dh Weinberg, Ae Evrard, L Hernquist, N Katz
Cosmological Simulations With Scale-Free Initial Conditions. I. Adiabatic Hydrodynamics, Jm Owen, Dh Weinberg, Ae Evrard, L Hernquist, N Katz
Astronomy Department Faculty Publication Series
We analyze hierarchical structure formation based on scale-free initial conditions in an Einstein-de Sitter universe, including a baryonic component with Ωbary = 0.05. We present three independent, smoothed particle hydrodynamics (SPH) simulations, performed at two resolutions (323 and 643 dark matter and baryonic particles) and with two different SPH codes (TreeSPH and P3MSPH). Each simulation is based on identical initial conditions, which consist of Gaussian-distributed initial density fluctuations that have a power spectrum P(k) k-1. The baryonic material is modeled as an ideal gas subject only to shock heating and adiabatic heating …