The Local Volume HI Survey

Circinus Galaxy (HIPASS J1413-65) is a highly obscured, late-type spiral galaxy with a very large, warped HI disc (Freeman et al. 1977; Jones et al. 1999; Curran et al. 2008; For, Koribalski & Jarrett 2012). It is located behind the Galactic Plane (at l,b = 311.3 degr, -3.8 degr), which makes it difficult to study its optical properties and large-scale environment due to high stellar density and dust extinction (A_B = 5.3 mag, Schlafly & Finkbeiner 2011). For the same reason, the distance to Circinus is still rather uncertain.

Based on a variety of methods, Freeman et al. (1977) derived an approximate distance of 4.2 ± 0.8 Mpc, which we adopt here. Karachentsev et al. (2007) estimated D_TF = 2.82 ± 0.28 Mpc using 2MASS infrared magnitudes, while Karachentsev et al. (2013) give D_TF = 4.2 Mpc. Freeman et al. (1977) determine de Vaucouleurs (B_24.5) and Holmberg (B_26.6) optical diameters for the Circinus Galaxy of 11.9 arcmin and 17.2 arcmin, respectively, after extinction correction (their Table 3) as well as PA = 210 degr and i = 65 degr. They give L_B = 7.2 × 10⁹ Lsun.

Using our ATCA HI mosaic we find an enormous HI envelope for the Circinus Galaxy, extending over 60 arcmin (at the outermost HI contour), well beyond the optical Holmberg radius. We measure an D_HI = 48.7 arcmin at 1 M_☉ pc^-2. Its large HI extent was also noted in the HI surveys of the Zone of Avoidance (HIZOA, Juraszek et al. 2000, Staveley-Smith et al. 2016) and in HIPASS (Koribalski et al. 2004). The ATCA HI distribution and mean HI velocity field of the Circinus galaxy, obtained with a 12-pointing mosaic in the 375-m configuration, show its large-scale warped HI disc.

For, Koribalski & Jarrett (2012) analyse high-resolution Spitzer mid-infrared images of the Circinus Galaxy and compare with Parkes and ATCA HI data. They derive star formation rates and analyse the local star formation conditions. The ionized gas in Circinus was studied by Elmouttie et al. (1998a) via Fabry-Perot Hα imaging. No GALEX UV images are available yet. Circinus also hosts bipolar radio lobes extending perpendicular to the inner disc (Elmouttie et al. 1998b, Wilson et al. 2011).

The large HI discs of Circinus and M 83 are typical for their HI mass (see Wang et al. 2016) and allow us to obtain accurate rotation curves out to radii of ~50 kpc. Using 3D FAT Kamphuis et al. (2015) obtain an HI rotation curve indicating v_rot = 161.4 km/s at R_max = 47.2 kpc (for i = 62.2 degr and PA = 199.6 degr) and M_dyn = 2.9 × 10¹¹ M_☉.

Reference: Koribalski et al. 2018 * LVHIS database * LVHIS homepage * next