EDP Sciences
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Volume 385, Number 1, April I 2002
Page(s) 21 - 31
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020042

A&A 385, 21-31 (2002)
DOI: 10.1051/0004-6361:20020042

New distances to galaxies in the Centaurus A group

I. D. Karachentsev1, M. E. Sharina1, 2, A. E. Dolphin3, E. K. Grebel4, D. Geisler5, P. Guhathakurta6, 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  UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
7  Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA
8  Astronomical Observatory of Kiev University, 04053, Observatorna 3, Kiev, Ukraine
9  Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
10  Department of Astronomy, University of Michigan, 830 Dennison Building, Ann Arbor, MI 48109, USA

(Received 6 November 2001 / Accepted 8 January 2002 )

We present Hubble Space Telescope/WFPC2 images of seventeen dwarf galaxies in the Centaurus A group. Their distances derived from the magnitudes of the tip of the red giant branch are 5.2 Mpc (KK112), 3.2 Mpc (ESO 321-014), 3.5 Mpc (KK179), 3.4 Mpc (NGC 5102), 4.6 Mpc (KK200), 3.7 Mpc (ESO 324-024), 4.7 Mpc (KK208), 4.6 Mpc (ESO 444-084), 4.4 Mpc (IC 4316), 4.5 Mpc (NGC 5264), 3.6 Mpc (KK211), 3.6 Mpc (KK213), 3.4 Mpc (ESO 325-011), 3.8 Mpc (KK217), 4.0 Mpc (KK221), 4.8 Mpc (NGC 5408), and 3.6 Mpc (PGC 51659). The galaxies are concentrated in two spatially separated groups around NGC 5128 = Cen A and NGC 5236 = M 83. The Cen A group itself has a mean distance of $3.63\pm 0.07$ Mpc, a velocity dispersion of 89 km s -1, a mean projected radius of 263 kpc, an estimated orbital mass of $2.1\times 10^{12} M_{\odot}$, and an orbital mass-to-blue luminosity ratio of 64 $M_{\odot}/L_{\odot}$. For the M 83 group we derived a mean distance of $4.57\pm 0.05$ Mpc, a velocity dispersion of 62 km s -1, a mean projected radius of 142 kpc, an estimated orbital mass of $0.8\times 10^{12} M_{\odot}$, and $M_{\rm orb}/L_{\rm B} = 37~M_{\odot}/L_{\odot}$. The M 83 group moves away from the Cen A group, which yields a radius of the zero-velocity surface of the Cen A group of R0 < 1.26 Mpc. The total mass within $R_0, M_0 < 2.7\times 10^{12} M_{\odot}$, agrees with the orbital mass estimate. The centroids of both the groups have very small peculiar velocities, $(+18\pm 24)$ km s -1 (Cen A) and ( $-17\pm27$) km s -1 (M 83) with respect to the local Hubble flow with H0 = 70 km s -1 Mpc -1.

Key words: galaxies: dwarf -- galaxies: distances and redshifts -- galaxies: general

Offprint request: I. D. Karachentsev, ikar@luna.sao.ru

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