Περίληψη:
Context. The study of the distribution, morphology, and kinematics of
cold molecular gas in the nuclear and circumnuclear regions of active
galactic nuclei (AGNs) helps to characterise and hence to quantify the
impact of the AGNs on the host galaxy over its lifetime. Aims. We
present the analysis of the molecular gas in the nuclear regions of
three Seyfert galaxies, NGC 4968, NGC 4845, and MCG-06-30-15, using
Atacama Large sub-Millimetre Array (ALMA) observations of the CO(2-1)
emission line. The aim is to determine the kinematics of the gas in the
central (similar to 1 kpc) region and thereby to probe nuclear fueling
and feedback of AGNs.
Methods. We used two different softwares, namely the 3D-Based Analysis
of Rotating Object via Line Observations and DiskFit, to model the
kinematics of the gas in the molecular disc, and thereby to determine
the gas rotation and any kinematical perturbations.
Results. Circular motions dominate the kinematics of the molecular gas
in the central discs, mainly in NGC 4845 and MCG-06-30-15; however there
is clear evidence of non-circular motions in the central (similar to 1
kpc) region of NGC 4845 and NGC 4968. The strongest non-circular motion
is detected in the inner disc of NGC 4968, mainly along the minor
kinematic axis, with a velocity similar to 115 km s(-1). Of all DiskFit
models, the bisymmetric model is found to give the best fit for NGC 4968
and NGC 4845, indicating that the observed non-circular motions in the
inner disc of these galaxies could result from the nuclear barred
structure, where the gas streams in elliptical orbits aligned along the
bar. If the dynamics of NGC 4968 is modelled as a corotation pattern
just outside of the bar, the bar pattern speed becomes Omega(b) = 52 km
s(-1) kpc(-1); the corotation is set at 3.5 kpc; and the inner Lindblad
resonance (ILR) ring is R=300 pc, corresponding to the CO emission ring.
In the NGC 4968 galaxy, the torques exerted on the gas by the bar are
positive in the centre, within the gas nuclear ring, and negative
outside. This shows that the gas is transiently trapped in the ILR. The
comparison of the CO intensity maps with the map of the cold dust
emission shows an absence of CO in the centre of NGC 4968; also the dust
distribution and CO emission in and around the centre of NGC 4845 have
similar extensions. The 1.2 mm ALMA continuum is peaked and compact in
NGC 4968 and MCG-06-30-15, but their CO(2-1) emissions have extended
distributions. Allowing the CO-to-H-2 conversion factor alpha(CO)
between 0.8 and 3.2, which is typical of nearby galaxies of the same
type, the molecular mass M(H-2) is estimated to be similar to 3 - 12 x
10(7)M(circle dot) (NGC 4968), similar to 9 - 36 x 10(7) M-circle dot
(NGC 4845), and similar to 1 - 4 x 10(7) M-circle dot (MCG-06-30-15).
Conclusions. We conclude that the observed non-circular motions in the
molecular disc of NGC 4968 and likely those seen in NGC 4845 are due to
the presence of the bar in the nuclear region. We discuss the
possibility that the observed pattern in the kinematics might be a
consequence of the presence of AGNs, and this might be the case for NGC
4845. At the current spectral and spatial resolution and sensitivity, we
cannot claim any strong evidence in these sources of the long sought
feedback or feeding effect resulting from the presence of AGNs.
Συγγραφείς:
Belete, A. Bewketu
Andreani, P.
Fernandez-Ontiveros, J. A. and
Hatziminaoglou, E.
Combes, F.
Sirressi, M.
Slater, R. and
Ricci, C.
Dasyra, K.
Cicone, C.
Aalto, S.
Spinoglio, L.
and Imanishi, M.
De Medeiros, J. R.
