Distances to dwarf galaxies of the Canes Venatici I cloud
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We determined the spatial structure of the scattered concentration of galaxies in the Canes Venatici constellation. We redefined the distances for 30 galaxies of this region using the deep images from the Hubble Space Telescope archive with the WFPC2 and ACS cameras.We carried out a high-precision stellar photometry of the resolved stars in these galaxies, and determined the photometric distances by the tip of the red giant branch (TRGB) using an advanced technique and modern calibrations. High accuracy of the results allows us to distinguish the zone of chaotic motions around the center of the system. A group of galaxies around M94 is characterized by the median velocity V LG = 287 km/s, distance D = 4.28 Mpc, internal velocity dispersion σ = 51 km/s and total luminosity L B = 1.61 × 1010 L ⊗. The projection mass of the system amounts to M p = 2.56 × 1012 M ⊗, which corresponds to the mass-luminosity ratio of (M/L) p = 159 (M/L)⊗. The estimate of the mass-luminosity ratio is significantly higher than the typical ratio M/L B ∼ 30 for the nearby groups of galaxies. The CVn I cloud of galaxies contains 4–5 times less luminous matter compared with the well-known nearby groups, like the Local Group, M81 and CentaurusA. The central galaxy M94 is at least 1m fainter than any other central galaxy of these groups. However, the concentration of galaxies in the Canes Venatici may have a comparable total mass.
Keywordsgalaxies: distances and redshifts galaxies: dwarf cosmology: dark matter
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