Environmental Engineering Reference
In-Depth Information
Chapter 11
T IDAL E NERGY E FFECTS OF D ARK M ATTER
H ALOS ON E ARLY -T YPE G ALAXIES
T. Valentinuzzi, R. Caimmi and M. D'Onofrio
Astronomy Dept., Padua Univ., Padova, Italy
Abstract
Tidal interactions between neighboring objects span across the whole admissible range
of lengths in nature: from, say, atoms to clusters of galaxies i.e. from micro to macro-
cosms. According to current cosmological theories, galaxies are embedded within
massive non-baryonic dark matter (DM) halos, which affects their formation and evo-
lution. It is therefore highly rewarding to understand the role of tidal interaction be-
tween the dark and luminous matter in galaxies. The current investigation is devoted
to Early-Type Galaxies (ETGs), looking in particular at the possibility of establishing
whether the tidal interaction of the DM halo with the luminous baryonic component
may be at the origin of the so-called “tilt” of the Fundamental Plane (FP). The ex-
tension of the tensor virial theorem to two-component matter distributions implies the
calculation of the self potential energy due to a selected subsystem, and the tidal po-
tential energy induced by the other one. The additional assumption of homeoidally
striated density profiles allows analytical expressions of the results for some cases of
astrophysical interest. The current investigation raises from the fact that the profile of
the (self + tidal) potential energy of the inner component shows maxima and minima,
suggesting the possible existence of preferential scales for the virialized structure, i.e.
a viable explanation of the so called ”tilt” of the FP. It is found that configurations
related to the maxima do not suffice, by themselves, to interpret the FP tilt, and some
other relation has to be looked for.
1.
Introduction
According to current cosmological theories, about 85 % of existing mass in the universe
is in the form of (non baryonic) dark matter (hereafter quoted as DM), whose tidal energy
effects on the embedded (baryonic) matter could be large. Since the first evidence of DM
presence in galaxy clusters (e.g., Zwicky, 1933), the existence of massive, non baryonic
halos is consistent with present-day CMB surveys, large scale galaxy clusters studies, and
necessary, e.g., for a viable explanation of flat rotation curves well outside visible disks of
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