Particle Astrophysics Center

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Particle Astrophysics Center

Naperville, IL, United States

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Robertson B.E.,University of Chicago | Robertson B.E.,Enrico Fermi Institute | Robertson B.E.,California Institute of Technology | Kravtsov A.V.,University of Chicago | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

Eulerian hydrodynamical simulations are a powerful and popular tool for modelling fluids in astrophysical systems. In this work, we critically examine recent claims that these methods violate Galilean invariance of the Euler equations. We demonstrate that Eulerian hydrodynamics methods do converge to a Galilean-invariant solution, provided a well-defined convergent solution exists. Specifically, we show that numerical diffusion, resulting from diffusion-like terms in the discretized hydrodynamical equations solved by Eulerian methods, accounts for the effects previously identified as evidence for the Galilean non-invariance of these methods. These velocity-dependent diffusive terms lead to different results for different bulk velocities when the spatial resolution of the simulation is kept fixed, but their effect becomes negligible as the resolution of the simulation is increased to obtain a converged solution. In particular, we find that Kelvin-Helmholtz instabilities develop properly in realistic Eulerian calculations regardless of the bulk velocity provided the problem is simulated with sufficient resolution (a factor of 2-4 increase compared to the case without bulk flows for realistic velocities). Our results reiterate that high-resolution Eulerian methods can perform well and obtain a convergent solution, even in the presence of highly supersonic bulk flows. © 2009 RAS.


Percival W.J.,University of Portsmouth | Reid B.A.,Autonomous University of Barcelona | Reid B.A.,University of Barcelona | Reid B.A.,Princeton University | And 27 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy sample represents the final set of galaxies observed using the original SDSS target selection criteria. We analyse the clustering of galaxies within this sample, including both the luminous red galaxy and main samples, and also include the 2-degree Field Galaxy Redshift Survey data. In total, this sample comprises 893 319 galaxies over 9100 deg2. Baryon acoustic oscillations (BAO) are observed in power spectra measured for different slices in redshift; this allows us to constrain the distance-redshift relation at multiple epochs. We achieve a distance measure at redshift z = 0.275, of r s(zd)/DV(0.275) = 0.1390 ± 0.0037 (2.7 per cent accuracy), where rs(zd) is the comoving sound horizon at the baryon-drag epoch, DV(z) ≡ [(1 + z) 2D2 Acz/H(z)]1/3, DA(z) is the angular diameter distance and H(z) is the Hubble parameter. We find an almost independent constraint on the ratio of distances DV(0.35)/ DV(0.2) = 1.736 ± 0.065, which is consistent at the 1.1σ level with the best-fitting Λ cold dark matter model obtained when combining our z = 0.275 distance constraint with the Wilkinson Microwave Anisotropy Probe 5-year (WMAP5) data. The offset is similar to that found in previous analyses of the SDSS DR5 sample, but the discrepancy is now of lower significance, a change caused by a revised error analysis and a change in the methodology adopted, as well as the addition of more data. Using WMAP5 constraints on Ωbh2 and Ωc h 2, and combining our BAO distance measurements with those from the Union supernova sample, places a tight constraint on Ωm = 0.286 ± 0.018 and H0 = 68.2 ± 2.2 km s-1 Mpc -1 that is robust to allowing Ωk ≠ 0 and w ≠ -1. This result is independent of the behaviour of dark energy at redshifts greater than those probed by the BAO and supernova measurements. Combining these data sets with the full WMAP5 likelihood constraints provides tight constraints on both Ωk = -0.006 ± 0.008 and w = -0.97 ± 0.10 for a constant dark energy equation of state. © 2009 RAS.


Reid B.A.,Autonomous University of Barcelona | Reid B.A.,University of Barcelona | Reid B.A.,Princeton University | Percival W.J.,University of Portsmouth | And 31 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the power spectrum of the reconstructed halo density field derived from a sample of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) Seventh Data Release (DR7). The halo power spectrum has a direct connection to the underlying dark matter power for k ≤ 0.2 h Mpc-1, well into the quasi-linear regime. This enables us to use a factor of ~8 more modes in the cosmological analysis than an analysis with kmax = 0.1 h Mpc-1,aswas adopted in the SDSS team analysis of the DR4 LRG sample. The observed halo power spectrum for 0.02


Kazin E.A.,New York University | Blanton M.R.,New York University | Scoccimarro R.,New York University | McBride C.K.,Vanderbilt University | And 9 more authors.
Astrophysical Journal | Year: 2010

We examine the correlation function ξ of the Sloan Digital Sky Survey Luminous Red Galaxy sample at large scales (60 h -1 Mpc < s < 400h -1Mpc) using the final data release (DR7). Focusing on a quasi-volume-limited (0.16 < z < 0.36) subsample and utilizing mock galaxy catalogs, we demonstrate that the observed baryonic acoustic peak and larger scale signal are consistent with ΛCDM at 70%-95% confidence. Fitting data to a non-linear, redshift-space, template-based model, we constrain the peak position at s p = 101.7 3.0h -1Mpc when fitting the range 60 h -1 Mpc < s < 150h -1Mpc (1σ uncertainties). This redshift-space distance s p is related to the comoving sound horizon scale rs after taking into account matter-clustering non-linearities, redshift distortions, and galaxy-clustering bias. Mock catalogs show that the probability that a DR7-sized sample would not have an identifiable peak is at least 10%. As a consistency check of a fiducial cosmology, we use the observed s p to obtain the distance relative to the acoustic scale. We find rs /DV (z = 0.278) = 0.1389 0.0043. This result is in excellent agreement with Percival et al., who examine roughly the same data set, but use the power spectrum. Comparison with other determinations in the literature are also in very good agreement. The signal of the full sample at 125 h -1 Mpc < s < 200h -1Mpc tends to be high relative to theoretical expectations; this slight deviation can probably be attributed to sample variance. We have tested our results against a battery of possible systematic effects, finding all effects are smaller than our estimated sample variance. © 2010. The American Astronomical Society.

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