arXiv subjects

Bruce A. Peterson

Publications and source records attributed to Bruce A. Peterson.

21 records · Page 2Linked to original sources

arXiv2001

Evidence for a non-zero Lambda and a low matter density from a combined analysis of the 2dF Galaxy Redshift Survey and Cosmic Microwave Background Anisotropies

We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n_s and n_t. On its own, the 2dFGRS sets tight limits on the parameter combination Omega_m h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega_b/Omega_m. The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a `geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons and cold dark matter. Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a pm 2sigma range of 0.65 < Omega_Lambda < 0.85, completely independently of constraints on Omega_Λderived from Type Ia supernovae.

astro-ph↗

arXiv2001

The 2dF Galaxy Redshift Survey: The power spectrum and the matter content of the universe

The 2dF Galaxy Redshift Survey has now measured in excess of 160000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct FFT-based technique. We argue that, within the k-space region 0.02<k<0.15 h Mpc^-1, the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analyzed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68% confidence limits on the total matter density times the Hubble parameter Ω_m h = 0.20 +/- 0.03, and the baryon fraction Ω_b/Ω_m = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.

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arXiv1997

Merging History Trees of Dark Matter Haloes: a Tool for Exploring Galaxy Formation Models

A method of deriving and using merging history trees of dark matter galaxy haloes directly from pure gravity N-body simulations is presented. This combines the full non-linearity of N-body simulations with the flexibility of the semi-analytical approach. Merging history trees derived from power-law initial perturbation spectrum simulations (for indices $n=-2$ and $n=0$) by Warren et al. (1992) are shown. As an example of a galaxy formation model, these are combined with evolutionary stellar population synthesis, via simple scaling laws for star formation rates, showing that if most star formation occurs during merger-induced bursts, then a nearly flat faint-end slope of the galaxy luminosity function may be obtained in certain cases. Interesting properties of hierarchical halo formation are noted: (1) In a given model, merger rates may vary widely between individual haloes, and typically 20%-30% of a halo's mass may be due to infall of uncollapsed material. (2) Small mass haloes continue to form at recent times: as expected, the existence of young, low redshift, low metallicity galaxies (e.g., Izotov et al. 1997) is consistent with hierarchical galaxy formation models. (3) For $n=-2,$ the halo spatial correlation function can have a very high initial bias due to the high power on large scales.

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