Bibcode
Krajnović, Davor; Bacon, R.; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. T.; Emsellem, Eric; Falcón-Barroso, Jesús; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; Sarzi, Marc; van den Bosch, Remco C. E.; van de Ven, Glenn
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 390, Issue 1, pp. 93-117.
Advertised on:
10
2008
Citations
174
Refereed citations
162
Description
We analysed two-dimensional maps of 48 early-type galaxies obtained with
the SAURON and OASIS integral-field spectrographs using kinemetry, a
generalization of surface photometry to the higher order moments of the
line-of-sight velocity distribution (LOSVD). The maps analysed include:
reconstructed image, mean velocity, velocity dispersion, h3
and h4 Gauss-Hermite moments. Kinemetry is a good method to
recognize structures otherwise missed by using surface photometry, such
as embedded discs and kinematic subcomponents. In the SAURON sample, we
find that 31 per cent of early-type galaxies are single component
systems. 91 per cent of the multicomponents systems have two kinematic
subcomponents, the rest having three. In addition, 29 per cent of
galaxies have kinematically decoupled components, nuclear components
with significant kinematic twists. We differentiate between slow and
fast rotators using velocity maps only and find that fast-rotating
galaxies contain discs with a large range in mass fractions to the main
body. Specifically, we find that the velocity maps of fast rotators
closely resemble those of inclined discs, except in the transition
regions between kinematic subcomponents. This deviation is measured with
the kinemetric k5/k1 ratio, which is large and
noisy in slow rotators and about 2 per cent in fast rotators. In terms
of E/S0 classification, this means that 74 per cent of Es and 92 per
cent of S0s have components with disc-like kinematics. We suggest that
differences in k5/k1 values for the fast and slow
rotators arise from their different intrinsic structure which is
reflected on the velocity maps. For the majority of fast rotators, the
kinematic axial ratios are equal to or less than their photometric axial
ratios, contrary to what is predicted with isotropic Jeans models viewed
at different inclinations. The position angles of fast rotators are
constant, while they vary abruptly in slow rotators. Velocity dispersion
maps of face-on galaxies have shapes similar to the distribution of
light. Velocity dispersion maps of the edge-on fast rotators and all
slow rotators show differences which can only be partially explained
with isotropic models and, in the case of fast rotators, often require
additional cold components. We constructed local (bin-by-bin)
h3-V/σ and h4-V/σ diagrams from SAURON
observations. We confirm the classical anticorrelation of h3
and V/σ, but we also find that h3 is almost zero in
some objects or even weakly correlated with V/σ. The distribution
of h4 for fast and slow rotators is mildly positive on
average. In general, fast rotators contain flattened components
characterized by a disc-like rotation. The difference between slow and
fast rotators is traceable throughout all moments of the LOSVD, with
evidence for different intrinsic shapes and orbital contents and, hence,
likely different evolutionary paths.