#### Document Type

Article

#### Publication Date

9-21-2001

#### Publication Title

Monthly Notices of the Royal Astronomical Society

#### Abstract

We compare the peculiar velocities derived from the *I*-band Tully–Fisher (TF) relation for 989 field spiral galaxies in the SFI catalogue with the predicted velocity field derived from the *IRAS* PSC*z* galaxy redshift survey. We assume linear gravitational instability theory and apply the maximum likelihood technique, VELMOD to SFI galaxies within a redshift *cz LG =6000 km s ^{−1}.* The resulting calibration of the TF relation is consistent with a previous, independent calibration for a similar sample of spirals residing in clusters. Our analysis provides an accurate estimate of the quantity

*β*, where

_{I}≡ Ω_{m}^{0.6}/b_{I}*b*

_{I}is the linear biasing parameter for IRAS galaxies. Using the forward TF relation and smoothing the predicted velocity field with a Gaussian filter of radius 300 km s

^{−1}, we obtain

*β*(1

_{I}=0.42±0.04*σ*uncertainty). This value, as well as other parameters in the fit, are robust to varying the smoothing radius to 500 km s

^{−1}and splitting the sample into spherical shells in redshift space. The one exception is the small-scale velocity dispersion,

*σ*

_{v}, which varies from ∼ 200 km s

^{−1}(within

*cz*LG =4000 km s

^{−1}) to ∼ 500 km s

^{−1}at larger distance. For

*β*, the residuals between the TF data and the PSC

_{I}≃0.42*z*gravity field are uncorrelated, indicating that the model provides a good fit to the data. More generally, a

*χ*

^{2}statistic indicates that the PSC

*z*model velocity field provides an acceptable (3

*σ*) fit to the data for

*0.3<β*.

_{I}<0.5#### DOI

10.1046/j.1365-8711.2001.04671.x

#### Recommended Citation

Branchini, E.; Freudling, W.; Da Costa, L. N.; Frenk, C. S.; Giovanelli, R.; Haynes, M. P.; Salzer, J. J.; Wegner, G.; and Zehavi, I., "Comparing the SFI Peculiar Velocities with the PSCz Gravity Field: A VELMOD Analysis" (2001). *Open Dartmouth: Faculty Open Access Articles*. 1865.

https://digitalcommons.dartmouth.edu/facoa/1865