5 research outputs found
On the Characteristic Isolation of Compact Subgroups within Loose Groups of Galaxies
We have explored the hypothesis that compact subgroups lying within dense
environments as loose groups of galaxies, at a certain stage of their
evolutionary history, could be influenced by the action of the tidal field
induced by the gravitational potential of the whole system. We argue that empty
rings observed in projection around many compact subgroups of galaxies embedded
in larger hosts originate around the spherical surface drawn by the tidal
radius where the internal binding force of the compact subgroup balances the
external tidal force of the whole system. This effect would torn apart member
galaxies situated in this region determining a marked isolation of the
subgroups from the rest of the host groups. If so, subsequent evolution of
these subgroups should not be affected by external influences as the infall of
new surrounding galaxies on them. Following this idea we have developed a
statistical method of investigation and performed an application to show
evidences of such effect studying a loose group of galaxies hosting a compact
group in its central region. The system UZC 578 / HCG 68 seems to be a fair
example of such hypothesized process.Comment: 12 pages, match version accepted for publication in TOAJ, corrected
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On the Adromeda to Milky Way mass-ratio
We have explored the hypothesis that the total mass-ratio of the two main
galaxies of the Local Group: Andromeda Galaxy(M31) and the Milky Way (MW) can
be constrained measuring the tidal force induced by the surrounding mass
distribution, M31 included, on the MW. We argue that the total mass-ratio
between the two groups can be approximated, at least qualitatively, finding the
tidal radius where the internal binding force of the MW balances the external
tidal force acting on it. Since M31 is the massive tidal perturber of the local
environment, we have used a wide range of M31 to MW mass-ratio combinations to
compute the corresponding tidal radii. Of them, only few match the distance of
the zero-tidal shell i.e. the shell identified observationally by the outermost
dwarf galaxies which do not show any sign of tidal effects. This is the key to
constrain the best mass-ratio interval of the two galaxies. Our results favour
a solution where the mass-ratio ranges from 2 to 3 implying a massive
predominance of M31.Comment: 8 pages, 2 figures, Accepted for publication in Mon. Not. of Royal
Astron. So