Kinematical Study of the Circumnuclear
Region of NGC 4321with INTEGRAL at WHT
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A. Castillo-Morales , E. Mediavilla , J. Jiménez-Vicente , A. Guijarro , E. Florido , E. Battaner
(1) Dept. de Física Teórica y del Cosmos, Universidad de Granada, E-18071, Spain
(2) Instituto de Astrofísica de Canarias, E-38200-La Laguna, Tenerife, Spain
The 2D spectroscopy with optical fibres allows us to obtain simultaneously spatial and spectral information for
extended objects. We present 2D spectroscopy of the circumnuclear region of the spiral Virgo cluster galaxy NGC
4321. Integral field spectroscopy in its central region has been obtained using the three fibre bundles of INTEGRAL at
WHT. The data are used to study the ionized gas and stellar kinematics.
Ionized gas
iThe Ha intensity map shows the emission
distributed in an ovally shaped ring where
several HII regions can be distinguished.
iThe velocity map shows clear
deviations from circular motions, some of
them related to the spiral arms.
Ha intensity map of the inner region of NGC 4321.
Observed nuclear spectrum of NGC 4321 in the full
spectral range (5790 - 6900 Å for SB3 fibre bundle).
We identify the emission lines of Ha+[N II] ll6548,
6583 and [S II] ll6716, 6731. This new data set
observed with INTEGRAL also shows a prominent
stellar absorption line (Na II l5890) which allows us,
for the first time, to compute stellar velocity maps
for this galaxy.
Stars
iThe stellar continuum map shows a
nuclear component surrounded by
several smaller spots following the shape
of the star formation ring.
i The velocity map associated with the
Na II absorption line is computed for the
first time in this galaxy.
Continuum map computed near the NaII absorption line.
Ha velocity field of the inner region of NGC 4321.
Stellar velocity map computed from the NaII absorption line.
Velocity field model (left) and residual velocity map (right) of the ionized Ha gas in
NGC 4321. Contour levels are spaced in steps of 10 km/s and 7 km/s respectively.
HST/WFPC2 (F555W) image of NGC 4321 with white contours of Ha (left) and
stellar (right) velocity fields overlaid.
Results
iThe Ha velocity field in the inner region of this galaxy shows the basic spider pattern
which indicates circular motions in a rotating disk and at the same time the effect of noncircular motions. The isovelocity contours are deformed following the structure of the spiral
arms.
Ha rotation curve of the inner disc of NGC 4321 derived out to 15´´(1.2
kpc) from the galactic centre. The rotation curve was obtained by
fitting tilted rings to the observed velocity fields at different angular
resolutions. Red squares, blue triangles and black diamonds
correspond to the SB3, SB2 and SB1 fibre bundles respectivley.
i We have derived the Ha rotation curve out to 15” using the three available INTEGRAL
angular resolutions. This curve shows a steep rise in the rotation velocity, reaching almost
130 km/s in 3”. The residual velocity map has been derived to study the presence of noncircular motions. The residuals show higher absolute values at the positions of the inner
spiral arms.
i The stellar velocity map derived from the Na II absorption line is complex. It shows a
dramatic difference between the stellar and the ionized gas velocity field, with the stellar
velocity map extremely distorted in its inner region.