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Willamette University Faculty Publications

Permanent Link: https://digitalcollections.willamette.edu/handle/10177/27712

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Browsing Willamette University Faculty Publications by Subject "cosmology"

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    Cosmic flows in the nearby universe from Type Ia supernovae
    (Oxford Academic, 2012-01-23) Turnbull, Stephen J.; Hudson, Michael J.; Feldman, Hume A.; Hicken, Malcolm; Kirshner, Robert P.; Watkins, Richard
    Peculiar velocities are one of the only probes of very large scale mass density fluctuations in the nearby Universe. We present new ‘minimal variance’ bulk flow measurements based upon the ‘First Amendment’ compilation of 245 Type Ia supernovae (SNe) peculiar velocities and find a bulk flow of 249 ± 76 km s−1 in the direction l= 319°± 18°, b= 7°± 14°. The SNe bulk flow is consistent with the expectations of Λ cold dark matter (ΛCDM). However, it is also marginally consistent with the bulk flow of a larger compilation of non-SNe peculiar velocities. By comparing the SNe peculiar velocities to predictions of the IRAS Point Source Catalogue Redshift Survey (PSCz) galaxy density field, we find Ω0.55mσ8,lin= 0.40 ± 0.07, which is in agreement with ΛCDM. However, we also show that the PSCz density field fails to account for 150 ± 43 km s−1 of the SNe bulk motion.
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    Cosmic flows on 100 h−1 Mpc scales: standardized minimum variance bulk flow, shear and octupole moments
    (Oxford Academic, 2010-07-22) Feldman, Hume A.; Watkins, Richard; Hudson, Michael J.
    The low-order moments, such as the bulk flow and shear, of the large-scale peculiar velocity field are sensitive probes of the matter density fluctuations on very large scales. In practice, however, peculiar velocity surveys are usually sparse and noisy, which can lead to the aliasing of small-scale power into what is meant to be a probe of the largest scales. Previously, we developed an optimal ‘minimum variance’ (MV) weighting scheme, designed to overcome this problem by minimizing the difference between the measured bulk flow (BF) and that which would be measured by an ideal survey. Here we extend this MV analysis to include the shear and octupole moments, which are designed to have almost no correlations between them so that they are virtually orthogonal. We apply this MV analysis to a compilation of all major peculiar velocity surveys, consisting of 4536 measurements. Our estimate of the BF on scales of ∼100 h−1 Mpc has a magnitude of |v| = 416 ± 78 km s −1 towards Galactic l= 282°± 11° and b= 6°± 6°. This result is in disagreement with Λ cold dark matter with Wilkinson Microwave Anisotropy Probe 5 (WMAP5) cosmological parameters at a high confidence level, but is in good agreement with our previous MV result without an orthogonality constraint, showing that the shear and octupole moments did not contaminate the previous BF measurement. The shear and octupole moments are consistent with WMAP5 power spectrum, although the measurement noise is larger for these moments than for the BF. The relatively low shear moments suggest that the sources responsible for the BF are at large distances.
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    A slight excess of large-scale power from moments of the peculiar velocity field
    (Oxford Academic, 2011-06-01) Macaulay, E.; Feldman, H.; Ferreira, P.G.; Hudson, M.J.; Watkins, R.
    The peculiar motions of galaxies can be used to infer the distribution of matter in the Universe. It has recently been shown that measurements of the peculiar velocity field indicate an anomalously high bulk flow of galaxies in our local volume. In this paper, we find the implications of the high bulk flow for the power spectrum of density fluctuations. We find that analysing only the dipole moment of the velocity field yields an average power spectrum amplitude which is indeed much higher than the Λ cold dark matter (ΛCDM) value. However, by also including shear and octupole moments of the velocity field, and marginalizing over possible values for the growth rate, an average power spectrum amplitude which is consistent with the ΛCDM is recovered. We attempt to infer the shape of the matter power spectrum from moments of the velocity field, and find a slight excess of power on scales ∼1 h−1 Gpc.