is a barred spiral galaxy which is interacting with its
brightest neighbour, NGC 6215, and possibly also with two newly discovered
low-surface brightness galaxies (see Fig. 10). The galaxy group lies only
below the Galactic plane which explains the rather crowded
field in the optical. Recent measurements with the ATCA 375-m array revealed
an HI bridge between the two major galaxies and several extensions
of the gas envelope of NGC 6221 which can be attributed to tidal forces between
these galaxies (B. Koribalski et al., in prep.). Detailed studies of the
Figure:
H
emission from the nuclear region of the Circinus galaxy.
This is a very preliminary image taken with the TAURUS-2 Fabry-Perot
instrument at the Anglo-Australian Telescope (courtesy: B. Koribalski,
K. Taylor, J. Whiteoak). The angular resolution is 15.
H
line emission in NGC 6221 by Pence & Blackman (1984) revealed very
large non-circular motions of the ionized gas, possibly as a result of tidal
interactions and streaming motions along the bar. The HI distribution
of NGC 6221 (Fig. 11) is quite similar to the optical emission; the central
depression is caused by HI absorption which is observed over several
hundred kms-1. A nuclear ring is the most likely explanation regarding
the similarity of this galaxy to others discussed here, but further data
analysis is needed to confirm this idea. The HI velocity field looks
much more regular than the H
field which was reconstructed from
several long-slit spectra. The nuclear activity is characterised by star
formation and a weak Seyfert2 nucleus.
Figure:
HI distribution (contours) of NGC 6221 and neighbouring
galaxies overlaid onto the optical emission (greyscale) from the Digitized
Sky Survey (DSS). The contour levels are 0.15, 0.3, 0.6, 1.2, 2.25, 4.5, and
9 Jybeam-1 kms-1. Please note that no primary beam correction
has been applied here.
A tidal HI bridge is visible between NGC 6221 and its brightest
neighbour, NGC 6215 (
= 1555 kms-1). The two low-surface
brightness galaxies (BK_1:
1645 kms-1 and BK_2:
1510 kms-1) are newly discovered members of this
interacting group of galaxies.
These data have been obtained with the 375-m array of the ATCA (12 h).
The angular resolution is about .
Not much is known about NGC 6215, which is classified as a non-barred
spiral galaxy of type SAS5 (RC3). Its HI emission extends from
1450 to 1650 kms-1 (Fig. 10).
Figure: Left: HI distribution of NGC 6221. The contour levels
are 0.15, 0.3, 0.6, 0.9, 1.2, and 1.5 Jybeam-1 kms-1.
Right: Mean HI velocity field of NGC 6221. The contour levels
range from 1315 to 1615 kms-1, step 15 kms-1.
These data have been obtained with the 1.5-km array of the ATCA (12 h).
The resolution is
6.6 kms-1.