The Local Volume HI Survey

NGC 247 (HIPASS J0047-20) is a late-type spiral galaxy at a cepheid distance of 3.65 ± 0.17 Mpc (Madore et al. 2009). This value agrees with its TRGB distance estimate by Karachentsev et al. (2006). Our ATCA HI moment maps show a mildly warped, regularly rotating disc extending about a factor two beyond the stellar disc. We measure F_HI = 662.5 Jy km/s, about 10% higher than the HIPASS value (Koribalski et al. 2004).

High-resolution, single-pointing VLA HI maps were obtained by Carignan & Puche (1990b) and Ott et al. (2012), who measure F_HI = 528 ± 18 Jy km/s and 382.6 Jy km/s (VLA-ANGST project), respectively. Both are missing substantial amounts of HI gas due to the lack of very short baselines and limited field-of-view. NGC 247's closest neighbour is the dIrr galaxy ESO 540-G031 (HIPASS J0049-20; UGCA 015).

The large spiral galaxies NGC 247 and NGC 253, together with the dwarf galaxies ESO 540-G030, ESO 540-G031 and ESO 540-G032 form another small association (D ~ 4 Mpc) within the Sculptor Group.

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

In the following we briefly discuss three faint dwarf galaxies (ESO 540-G030, ESO 540-G031, and ESO 540-G032) near NGC 247; these are not part of the LVHIS galaxy atlas presented here. Karachentsev et al. (2003) obtained TRGB distances of 3.40 ± 0.34 Mpc (ESO 540-G030), 3.34 ± 0.24 Mpc (ESO 540-G031), and 3.42 ± 0.27 Mpc (ESO 540-G032), suggesting that this dwarf grouping lies slightly in front of the spiral galaxy NGC 247.

ESO 540-G030 is a low surface brightness dwarf galaxy. Jerjen et al. (1998, 2000) measured an integrated magnitude of B_T = 16.37 mag and an SBF distance of 3.19 ± 0.13 Mpc. In addition to a large number of red stars, Karachentsev et al. (2003) also detect a number of blue stars in the central region of ESO 540-G030, suggesting that it is a transition dSph/dIrr type galaxy. Deep Parkes and ATCA HI observations were presented by Bouchard et al. (2005), resulting in a tentative detection. They derive a total HI mass of 8.9 ± 1.9 × 10⁵ M_☉; and note a positional offset between the HI gas and the stellar component.

ESO 540-G031 (HIPASS J0049-20) is a dwarf irregular galaxy at a TRGB distance of 3.34 ± 0.24 Mpc (Karachentsev et al. 2003), located only 40 arcmin east of NGC 247. The HIPASS BGC gives F_HI = 3.9 ± 1.5 Jy km/s and v_sys = 294 km/s (Koribalski et al. 2004). HI maps of ESO 540-G031 (UGCA 015, DDO 6) obtained with the GMRT (Begum et al. 2008) and the VLA (Ott et al. 2012) show F_HI = 2.6 ± 0.3 and 1.2 Jy km/s, respectively. Using our low-resolution ATCA HI mosaic of NGC 247 and surroundings we measure F_HI ~ 3.2 Jy km/s for ESO 540-G031 and derive M_HI = 8.2 × 10⁶ M_☉ (see also Warren et al. 2007). The HI emission of ESO 540-G031 is offset towards the south-western side of the stellar body. Its relatively bright GALEX UV emission suggests significant star formation (SFR = 1.4 × 10^-3 M_☉/yr; Ott et al. 2012).

ESO 540-G032 is another transition-type dwarf galaxy. Parkes and ATCA HI data by Bouchard et al. (2005) suggest a centre velocity of 228 km/s. The detection was later confirmed by Da Costa et al. (2008) who also obtain new HST-ACS optical data, deriving a TRGB distance of 3.7 ± 0.2 Mpc and M_HI = 9.1 × 10⁵ M_☉. Their ATCA image shows an HI source with a faint eastern extension.

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