Bibcode
Balcells, Marc; Carter, David
Bibliographical reference
Astronomy and Astrophysics (ISSN 0004-6361), vol. 279, no. 2, p. 376-384
Advertised on:
11
1993
Citations
19
Refereed citations
17
Description
The velocity field of the central parts of the elliptical galaxy NGC
7626 has been mapped by obtaining high resolution curves and velocity
dispersion profiles for four slit position angles along the major, minor
and two intermediate photometric axes. Each rotation curve and
dispersion profile shows a high level of structure. Along the major
axis, the rotation curve reverses sign twice at each side of the center.
Along the minor axis, we find a velocity reversal at the core plus two
narrow (approximately 1 arcsec) regions of velocity reversal further
out, symmetrically placed with respect to the center. Similar narrow
features seen along other position angles suggest that we have detected
shells kinematically. We tentatively identify three kinematic regions,
the core, the intermediate region and the outer part. The rotation axis
of the core lies at 45 deg from the photometric major axis. The spin of
the intermediate region is opposite to that of the core, and that of the
outer part is roughly orthogonal. The core is not dynamically relaxed. A
merger/accretion is thus the most plausible origin for the peculiar
kinematics. The many dynamical components make NGC 7626 an outstanding
example of a core in the making. We analyze this system to infer clues
on late merger dynamics. The merger appears to increase the tangential
velocity dispersion and contribute to flatten the velocity dispersion
profile. We speculate that, once the system relaxes, orthogonal core and
main body rotation may be stabilized by long- and short-axis tube
orbits. We suggest that mergers may establish the net circulation in
tube orbits which is responsible for the kinematic twists in the
projected velocity fields of triaxial galaxies. The dynamical age of the
core is at most 108 years. A starburst of this age would be
expected to leave a signature in the spectrum of the galaxy, hence we
can rule out a starburst at a time of onset of the peculiar kinematic
features.