Local velocity field from sosie galaxies

Free access article

Issue		A&A Volume 393, Number 1, October I 2002


Page(s)		57 - 68
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20021018

A&A 393, 57-68 (2002)
DOI: 10.1051/0004-6361:20021018

I. The Peebles' model

J. N. Terry, G. Paturel and T. Ekholm

CRAL-Observatoire de Lyon, UMR 5574, 69230 Saint-Genis Laval, France

(Received 24 May 2000 / Accepted 20 June 2002 )

Abstract
Pratton et al. (1997) showed that the velocity field around clusters could generate an apparent distortion that appears as tangential structures or radial filaments. In the present paper we determine the parameters of the Peebles' model (1976) describing infall of galaxies onto clusters with the aim of testing quantitatively the amplitude of this distortion.

The distances are determined from the concept of sosie galaxies (Paturel 1984) using 21 calibrators for which the distances were recently calculated from two independent Cepheid calibrations. We use both B and I-band magnitudes.

The Spaenhauer diagram method is used to correct for the Malmquist bias. We give the equations for the construction of this diagram. We analyze the apparent Hubble constant in different regions around Virgo and obtain simultaneously the Local Group infall and the unperturbed Hubble constant. We found:

$\begin{displaymath}V_{\rm LG-infall} = 208 \pm 9~\rm km\,s^{-1}\end{displaymath}$

$\begin{displaymath}\log H = 1.82 \pm 0.04 \ \ \ \left(H \approx 66 \pm 6~\rm km\,s^{-1}\,Mpc^{-1}\right).\end{displaymath}$

The front side and backside infalls can be seen around Virgo and Fornax. In the direction of Virgo the comparison is made with the Peebles' model. We obtain:

$\begin{displaymath}v_{\rm infall} = \frac{C_{\rm Virgo}}{r^{0.9 \pm 0.2}}\end{displaymath}$

with $C_{\rm Virgo}=2800$ for Virgo and $C_{\rm Fornax}=1350$ for Fornax, with the adopted units (km s ^-1 and Mpc).

We obtain the following mean distance moduli:

$\begin{displaymath}\mu _{\rm Virgo}=31.3 \pm 0.2 \ \ \ \left(r=18 \rm ~Mpc\right)\end{displaymath}$

$\begin{displaymath}\mu _{\rm Fornax}=31.7 \pm 0.3 \ \ \ \left(r=22\rm ~Mpc\right).\end{displaymath}$

All these quantities form an accurate and coherent system.

Key words: galaxies: general -- galaxies: distances and redshifts -- cosmology: distance scale -- methods: statistical

Offprint request: G. Paturel, patu@obs.univ-lyon1.fr

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