TITLE:
Kinematic Decoupled Core Paradigm: Counterrotation or Just Warping
AUTHORS:
Rubén J. Díaz, Horacio Dottori
KEYWORDS:
Galaxies Disks, Counterrotation, Inner Warps, Kinematics
JOURNAL NAME:
International Journal of Astronomy and Astrophysics,
Vol.6 No.2,
June
20,
2016
ABSTRACT: Several mechanisms
have been proposed in recent years to explain kinematic decoupled cores (KDCs)
in early type galaxies as well as the large differences in angular momentum
between KDCs and host galaxy. Most of the proposed scenarios involve large
fractions of merging events, high speed interactions with dwarf spheroidal
galaxies, cusp effect of the dark matter density profiles, etc. We here argue
that counterrotation as well as fast and slow rotation of disks or spheroids at
the center of galaxies can also be explained by a misalignment of the central
spheroid equatorial plane with regard to that defined by the observed external
stellar rotation. Contrary to what happens at the outer region of disk galaxies,
once instability has led to the inner warped core, the perturbed orbits can
maintain a common orientation due to the rigid body like rotation at the
central region of the galaxy. The spatial configuration that furnishes the
smallest angular momentum difference between the KDC and the host galaxy is
completely defined by observed parameters in the plane of the sky, namely, the
inclination of the inner and outer disks and the angle between the two lines of
nodes. As an example we modeled the paradigmatic and extreme case of the 2D
radial velocity field of NGC 4382 nucleus. Tilt angles of the KDC not larger
than 30 degrees also allow explaining fast and low rotators of the called
“Sauron paradigm” in a unified scenario. The maximum for the three parameters,
namely, velocity of the inner rotator, difference of position angle and
difference with the outer rotation velocity of the whole Sauron sample, are consistently
correlated in agreement with the proposed scenario. These quantities do not
correlate with the galaxies magnitude, mass (since large and dwarf spheroidals
show apparent counterrotation as well) or environment, also suggesting that an
internal phenomenon like the central spheroid warping, that we are here
proposing, may be at work.