#### Document Type

Article

#### Publication Date

9-21-2001

#### Publication Title

Monthly Notices of the Royal Astronomical Society

#### Department

Department of Physics and Astronomy

#### 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

#### Original Citation

E. Branchini, W. Freudling, L.N. Da Costa, C.S. Frenk, R. Giovanelli, M.P. Haynes, J.J. Salzer, G. Wegner, I. Zehavi, Comparing the SFI peculiar velocities with the PSCz gravity field: a VELMOD analysis, Monthly Notices of the Royal Astronomical Society, Volume 326, Issue 3, September 2001, Pages 1191–1204, https://doi.org/10.1046/j.1365-8711.2001.04671.x

#### Dartmouth Digital Commons 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). *Dartmouth Scholarship*. 1865.

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