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Next: NGC 7552 Up: The Group of Nearby Previous: Circinus

NGC 6221

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 $\sim10^{\circ}$ 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$\alpha$ 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 $\sim$15.
\begin{figure}
\plotfiddle{CIRCINUS_HA.PS}{10cm}{0}{60}{60}{-200}{-100}
\end{figure}

H$\alpha$ 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$\alpha$ 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 ($v_{\rm sys}$ = 1555 kms-1). The two low-surface brightness galaxies (BK_1: $v_{\rm sys} \sim$ 1645 kms-1 and BK_2: $v_{\rm sys} \sim$ 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 $1\farcm5$.
\begin{figure}
\plotone{NGC6221_GROUP_OVER.PS}
\end{figure}

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 $\sim$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 $30\arcsec \times 25\arcsec \times$ 6.6 kms-1.
\begin{figure}
\plottwo{NGC6221_HI.PS}{NGC6221_VEL.PS}
\end{figure}


next up previous
Next: NGC 7552 Up: The Group of Nearby Previous: Circinus
Baerbel Koribalski
2002-04-03