John P Huchra | Searcharxiv

arXiv1999

The HST Key Project on the Extragalactic Distance Scale. XXVIII. Combining the Constraints on the Hubble Constant

Since the launch of the Hubble Space Telescope nine years ago, Cepheid distances to 25 galaxies have been determined for the purpose of calibrating secondary distance indicators. A variety of these can now be calibrated, and the accompanying papers by Sakai, Kelson, Ferrarese, and Gibson employ the full set of 25 galaxies to consider the Tully-Fisher relation, the fundamental plane of elliptical galaxies, Type Ia supernovae, and surface brightness fluctuations. When calibrated with Cepheid distances, each of these methods yields a measurement of the Hubble constant and a corresponding measurement uncertainty. We combine these measurements in this paper, together with a model of the velocity field, to yield the best available estimate of the value of H_0 within the range of these secondary distance indicators and its uncertainty. The result is H_0 = 71 +/- 6 km/sec/Mpc. The largest contributor to the uncertainty of this 67% confidence level result is the distance of the Large Magellanic Cloud, which has been assumed to be 50 +/- 3 kpc.

astro-ph↗

arXiv1993

Clustering in the 1.2 Jy IRAS Galaxy Redshift Survey II: Redshift Distortions and ξ(r_p,π)

We examine the effect of redshift space distortions on the galaxy two-point correlation function $ξ(r_p,π)$ as a function of separations parallel ($r_p$) and perpendicular ($π$) to the line of sight. We find that the relative velocity dispersion of pairs of IRAS galaxies is $σ(r)= 317^{+40}_{-49}$ \kms at $r=1 \mpc$, consistent with previous estimates derived from optically selected galaxy catalogues. Unfortunately, the use of this result to estimate $Ω$ via the Cosmic Virial Theorem is thwarted by large systematic uncertainties. We also fit for the mean relative streaming velocity of pairs, $v_{12}(r)$, which describes the growth of fluctuations on both linear and nonlinear scales. We find that $v_{12}(r) = 167^{+99}_{-67}$ \kms at $r=4$\mpc, so that on average, approximately half the Hubble expansion velocity of pairs at this separation is canceled by infall. At $r=10$\mpc, the amplitude of the streaming is lower and $v_{12}(r) = 109^{+64}_{-47} \kms$. Linear perturbation theory then implies that $Ω^{0.6}/b =0.45^{+0.27}_{-0.18}$ on scales $\sim 10-15 \mpc$. The amplitude of $v_{12}(r)$ is sensitive to the assumed shape of $σ(r)$; if the latter deviates substantially from a virialized form on small scale, our best fit amplitude of $v_{12}(r)$ can deviate by a factor of two.

astro-ph↗