Pierre Chamaraux

The I-Band Tully-Fisher Relation for Sc Galaxies: 21 Centimeter H I Line Data

A compilation of 21 cm line spectral parameters specifically designed for application of the Tully-Fisher (TF) distance method is presented for 1201 spiral galaxies, primarily field Sc galaxies, for which optical I-band photometric imaging is also available. New H I line spectra have been obtained for 881 galaxies. For an additional 320 galaxies, spectra available in a digital archive have been reexamined to allow application of a single algorithm for the derivation of the TF velocity width parameter. A velocity width algorithm is used that provides a robust measurement of rotational velocity and permits an estimate of the error on that width taking into account the effects of instrumental broadening and signal-to-noise. The digital data are used to establish regression relations between measurements of velocity widths using other common prescriptions so that comparable widths can be derived through conversion of values published in the literature. The uniform H I line widths presented here provide the rotational velocity measurement to be used in deriving peculiar velocities via the TF method.

Statistical deprojection of galaxy pairs

Aims. The purpose of the present paper is to provide methods of statistical analysis of the physical properties of galaxy pairs. We perform this study to apply it later to catalogs of isolated pairs of galaxies, especially two new catalogs we recently constructed that contain ≈1000 and ≈13 000 pairs, respectively. We are particularly interested by the dynamics of those pairs, including the determination of their masses. Methods. We could not compute the dynamical parameters directly since the necessary data are incomplete. Indeed, we only have at our disposal one component of the intervelocity between the members, namely along the line of sight, and two components of their interdistance, i.e., the projection on the sky-plane. Moreover, we know only one point of each galaxy orbit. Hence we need statistical methods to find the probability distribution of 3D interdistances and 3D intervelocities from their projections; we designed those methods under the term deprojection. Results. We proceed in two steps to determine and use the deprojection methods. First we derive the probability distributions expected for the various relevant projected quantities, namely intervelocity vz, interdistance rp, their ratio, and the product rpvz , which is involved in mass determination. In a second step, we propose various methods of deprojection of those parameters based on the previous analysis. We start from a histogram of the projected data and we apply inversion formulae to obtain the deprojected distributions; lastly, we test the methods by numerical simulations, which also allow us to determine the uncertainties involved.

Spiral Galaxies and the Peculiar Velocity Field

We report results of a redshift-independent distance measurement survey that extends to all sky and out to a redshift of approximately 7500 km s-1. Tully—Fisher (TF) distances for a homogeneous sample of 1600 late spiral galaxies are used to analyze the peculiar velocity field. We find large peculiar velocities in the neighborhood of superclusters, such as Perseus- Pisces (PP) and Hydra—Centaurus, but the main clusters embedded in those regions appear to be virtually at rest in the CMB reference frame. We find no compelling evidence for large—scale bulk flows, whereby the Local Group, Hydra—Cen and PP would share a motion of several hundred km s-1 with respect to the CMB. Denser sampling in the PP region allows a clear detection of infail and backflow motions, which can be used to map the mass distribution in the supercluster and to obtain an estimate of the cosmological density parameter.