Centaurus A (NGC 5128)
NGC 5128 (HIPASS J1324-42)
is a nearby radio galaxy (DTRGB = 3.77 ± 0.38 Mpc;
Rejkuba 2004) with two giant lobes spanning ~8 degrees on the sky (ie., ~0.5
Mpc). It is the dominant elliptical galaxy in the Cen A / M 83 galaxy group,
which is known to contain ~100 members.
The bright and extended 20-cm radio continuum emission provides some technical
challenges for accurate HI measurements which are further complicated by the
presence of both HI emission and absorption over a wide velocity range (see
Koribalski et al. 2004).
Cen A's optical appearance is that of a giant elliptical surrounded by a
prominent band of highly opaque dust, which matches the HI disc detected with
the ATCA. Struve et al. (2010) measure FHI = 144 Jy km/s, somewhat
more than obtained by van Gorkom et al. (1990), and derive MHI =
4.9 × 108 M☉. For a comparison
with Parkes FHI measurements see the discussion in Koribalski
et al. (2004; their Section 3.6). Struve et al. (2010) obtain an HI extent
of 814 arcsec or 15 kpc and find a regular rotating, highly warped disc.
Further HI emission is detected in the outer disc, somewhat aligned
with the faint optical shells of Cen A and likely the result of gas accretion
in a recent merger event. Schiminovich et al. (1994) also find HI emission
associated with the diffuse shells of NGC 5128 and measure FHI
= 208 Jy km/s. Parkes HI spectra obtained by Gardner & Whiteoak (1976)
shows emission from ~250 to 850 km/s. Using HIPASS we estimate an HI mass
of at least 6 × 108 M☉.
Furthermore, we detect HI emission east and west of Cen A (sources A, B
and C in Fig. 14) without stellar counterparts. These could either be very
faint dwarf galaxies near Cen A or another set of HI shells. Their
α,δ(J2000) positions and HI properties are as follows. Source A:
13:28:39.9, -42:56:56.5 (~349 − 507 km/s, 35.4 arcmin east of Cen A,
FHI = 7.9 ± 1.1 Jy km/s; slightly elongated N−S);
source B: 13:23:46.2, -43:06:19.9 (~257 − 414 km/s, 19.2 arcmin west of
Cen A, unresolved in HIPASS), and source C: 13:21:16.9, -42:45:24.1 (~507
− 534 km/s, 48.5 arcmin east of Cen A, elongated NW−SE in HIPASS.
GALEX UV images do not reveal any counterparts.
Reference:
Koribalski et al. 2018
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