is a nearby spiral galaxy only 4
below the
Galactic plane. It was found while inspecting a Schmidt plate and shortly
afterwards observed in HI with the Parkes 64-m telescope. Freeman et
al. (1977) measured a half-width of at least
for the HI extent of Circinus, much larger than the optical diameter
(10) of the galaxy. K. Jones et al. (1996, in prep.) and
Koribalski & Whiteoak (1996) only recently mapped
Circinus with several configurations of the ATCA; a few preliminary results
are presented here. Fig. 7 shows part of the overall HI distribution,
clearly outlining the two spiral arms. The elongated central disk (length
5) indicates a bar, and the central `hole' is caused by HI
absorption against the bright central region of Circinus (see Fig. 8). The
nuclear activity is caused by star formation, a Seyfert2 nucleus and giant
Figure:
HI absorption spectrum toward the nuclear region of the
Circinus galaxy. These data were taken with the largest array of the ATCA
(Koribalski & Whiteoak 1996).
radio lobes (perhaps associated with outflow), very similar to those in
NGC 3079. Harnett et al. (1990) observed Circinus with Parkes at 1665 and
1667 MHz and found strong OH absorption lines over a velocity range of nearly
200 kms-1. High-resolution ATCA measurements reveal HI
absorption over about the same velocity range. The data show a shift of the
line over the face of the continuum, indicating a fast-rotating nuclear ring
(Koribalski & Whiteoak 1996). This is supported by H
images taken
with AAT Taurus Fabry-Perot interferometer (Fig. 9) and with the ESO New
Technology Telescope (Marconi et al. 1994) showing a broken ring or spiral
arms at 200 pc from the nucleus. Marconi et al. also found an
OIII emission cone toward the NW indicating highly ionized gas
flowing out from the nuclear region.