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Issue A&A
Volume 398, Number 2, February I 2003
Page(s) 467 - 477
Section Galactic structure and dynamics
DOI 10.1051/0004-6361:20021598



A&A 398, 467-477 (2003)
DOI: 10.1051/0004-6361:20021598

Galaxy flow in the Canes Venatici I cloud

I. D. Karachentsev1, M. E. Sharina1, 2, A. E. Dolphin3, E. K. Grebel4, D. Geisler5, P. Guhathakurta6, 7, P. W. Hodge7, V. E. Karachentseva8, A. Sarajedini9 and P. Seitzer10

1  Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR 369167, Russia
2  Isaac Newton Institute, Chile, SAO Branch
3  Kitt Peak National Observatory, National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85726, USA
4  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
5  Departamento de Física, Grupo de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
6  Herzberg Fellow, Herzberg Institute of Astrophysics, 5071 W. Saanich Road, Victoria, B.C. V9E 2E7, Canada
7  Permanent address: UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
8  Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA
9  Astronomical Observatory of Kiev University, 04053, Observatorna 3, Kiev, Ukraine
10  Department of Astronomy, University of Florida, Gainesville, FL 32611, USA

(Received 8 August 2002 / Accepted 25 October 2002)

Abstract
We present an analysis of Hubble Space Telescope/WFPC2 images of eighteen galaxies in the Canes Venatici I cloud. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical accuracy of ~ 12%. The resulting distances are 3.9 Mpc (UGC 6541), 4.9 Mpc (NGC 3738), 3.0 Mpc (NGC 3741), 4.5 Mpc (KK 109), > 6.3 Mpc (NGC 4150), 4.2 Mpc (UGC 7298), 4.5 Mpc (NGC 4244), 4.6 Mpc (NGC 4395), 4.9 Mpc (UGC 7559), 4.2 Mpc (NGC 4449), 4.4 Mpc (UGC 7605), 4.6 Mpc (IC 3687), 4.7 Mpc (KK 166), 4.7 Mpc (NGC 4736), 4.2 Mpc (UGC 8308), 4.3 Mpc (UGC 8320), 4.6 Mpc (NGC 5204), and 3.2 Mpc (UGC 8833). The CVn I cloud has a mean radial velocity of $286 \pm 9$ km s -1, a mean distance of $4.1 \pm 0.2$ Mpc, a radial velocity dispersion of 50 km s -1, a mean projected radius of 760 kpc, and a total blue luminosity of $2.2 \times 10^ L_{\sun}$. Assuming virial or closed orbital motions for the galaxies, we estimated their virial and their orbital mass-to-luminosity ratio to be 176 and 88  $ M_{\sun}/L_{\sun} $, respectively. However, the CVn I cloud is characterized by a crossing time of 15 Gyr, and is thus far from a state of dynamical equilibrium. The large crossing time for the cloud, its low content of dSph galaxies ( < 6%), and the almost "primordial" shape of its luminosity function show that the CVn I complex is in a transient dynamical state, driven rather by the free Hubble expansion than by galaxy interactions.


Key words: galaxies: dwarf -- galaxies: distances and redshifts -- galaxies: kinematics and dynamics -- galaxies: clusters: individual: canes venatici cloud

Offprint request: M. E. Sharina, sme@luna.sao.ru

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