The kinematics of the ionized gas in the Circinus galaxy

Abstract

The TAURUS‐2 Fabry–Perot interferometer, mounted on the 3.9‐m Anglo‐Australian Telescope, has been used to observe the Circinus galaxy. We have mapped the intensity and velocity distribution of the ionized hydrogen in the galaxy using the Balmer series Hα spectral line. The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non‐thermal source. A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s−1 (assuming circular motions) surrounds the core. The inclination angle of this feature, i=40°±10°, is less than that of the previously observed radio continuum disc. The velocity channel maps obtained for the Hα ring show that the kinematics resemble those of a rotating ring and the intensity displays a complex structure indicative of several, unresolved, H II regions. We believe the ring to represent a circumnuclear starburst. Our Hα data also show the presence of the previously detected [O III] ionization cone to the north‐west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s−1 for gas above the core of Circinus. We also present evidence for inflowing ionized gas at the centre of Circinus. The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst‐driven superwind in the Circinus galaxy.

Differences in the dense gas between type 1 and type 2 Seyferts

“…The model, which is discussed in more detail in Curran (1998);Curran (2000), provides a very satisfactory fit to the observed data in the Circinus galaxy, a type 2 Seyfert 8 , 8 Regarding the previous section, note that Circinus, the closest lying example of a Seyfert galaxy, has LFIR = 6.2 10 9 L (Lonsdale et al 1985) and LCO ≈ 30 10 3 K km s −1 kpc 2 (Curran 2000), thus giving the high CO/FIR luminosity ratio which agrees closely with other observations of the gas in this galaxy (Veilleux & Bland-Hawthorn 1997;Elmouttie et al 1998a;Elmouttie et al 1998b). Due to the close proximity of Circinus we could map the CO emission with the 22 beam at SEST, but since these galaxies are much further away, we have no such luxury (especially with the eight Southern galaxies) 9 .…”

“…Like Circinus (Marconi et al 1994;Veilleux & BlandHawthorn 1997;Elmouttie et al 1998b), NGC 1365 exhibits an ionisation cone Hjelm & Lindblad 1996) and since the model cannot distinguish the presence of an outflow of low inclination, we cannot exclude the presence of this (Curran 2000). It should be noted, however, that the served is quite asymmetric.…”

The Physical Conditions of the X‐Ray Emission Line Regions in the Circinus Galaxy

“…Nevertheless, these mass Ñow rates are roughly consistent with each other, and we suggest that the inner part of the X-ray emission region is fueling the central engine. Projected velocity shifts of up to D230 km s~1 have also been detected near the base of the [O III] and Ha ionization cones, which may be interpreted as either an outÑow or inÑow relative to the nucleus (Veilleux & BlandHawthorn 1997 ;Elmouttie et al 1998).…”

AChandraObservation of the Circinus Galaxy

“…The association of the other sources with the Circinus galaxy is less certain. Source F is close to, but not coincident with, a patch of Ha emission^27A south of the nucleus, possibly an H II region in a spiral arm of the galaxy (Elmouttie et al 1998). This X-ray source has a hard X-ray spectrum and presumably is an X-ray binary ; it may show a weak extension to the southwest (Fig.…”