Basic parameters

Centaurus A
( Cen A,  NGC 5128,  PKS 1322-427 ) 1)


NGC 5128 galaxy type: Ep  (Harris 2010)
Radio galaxy: Fanaroff-Riley class I
Unification scheme: misaligned BL Lac  (Chiaberge et al. 2001)

Coordinates (nucleus)

R.A. (J2000) = 13h25m27.s6152  (201.°3650633)
Declination (J2000) = -43°01'08."805 (-43°0191125)
l" = 309.°5158743
b" = 19.°4173247

Distance (to the central regions) 2)

3.8 ± 0.1 Mpc  (Harris et al. 2010);  1' ≈ 1.1 kpc (at 3.8 Mpc)
z ≈ 0.0009  (with H0 = 70 km s-1 Mpc-1)

Black hole mass 3)

(5.5 ± 3.0) x 107 Msun  (Cappellari et al. 2009)

Stellar mass

~ 1 x 1011 Msun

Jet power (present-day jet)

(1—2) x 1043 erg s-1  (Croston et al. 2009; Wykes et al. 2013; Neff et al. 2015a)

Age 4)

Parent massive elliptical galaxy: several Gyr
Radio galaxy: ∼ 560 Myr  (Wykes et al. 2013, Eilek 2014, Wykes et al. 2014)


Total integrated apparent magnitude: mV = 6.20  (Dufour et al. 1979)
Dereddened integrated magnitude and colours: V0,tot = 5.87, (B-V)0 = 0.84,
(U-B)0 = 0.36  (Dufour et al. 1979)


Cen A Location

Constellation Centaurus
Credit: IAU and Sky & Telescope magazine
(Roger Sinnott & Rick Fienberg)
Cen A Location

Milky Way panorama with the
location of Cen A overlaid.
Credit: Axel Mellinger

Nomenclature of the (radio) structures

In order to describe the position of various structures, researchers have traditionally resorted to radio observations. The Cen A radio morphology has been thoroughly discussed by Burns et al. (1983), Junkes et al. (1993), Israel (1998), Alvarez et al. (2000), Goodger et al. (2010), Feain et al. (2011), Müller et al. (2014) and Neff et al. (2015a).

More recently, some of Cen A's morphology has been described at other wavelengths as well, see e.g. Hardcastle et al. (2006), Kraft et al. (2009), Croston et al. (2009), Abdo et al. 2010, Goodger et al. (2010), Neff et al. (2015b), McKinley et al. (2018).

These pages offer the following guideline:
Cen A radio structure
Overview over the radio structure of Centaurus A. The whole radio (and gamma-ray) emitting
region extends about 9° on the sky. Currently, with VLBI techniques, structures of the jet and the 'core' corresponding to a resolution of 0.68 x 0.41 milliarcseconds can be resoved.
Source: Wikipedia

Multiwavelength composite of the central regions with
the inner lobes and the main jet to the north-east.
Credit: ESO/WFI (Optical);
MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre);
NASA/CXC/CfA/R.Kraft et al. (X-ray)

Some authors refer to the GLs as the extended source or the outer lobes. The inner lobes plus the region closer to the nucleus including the main jet are also referred to as the central source or the central component. The term inner jet refers in most instances to the more central parts of the kiloparsec-scale jet (to about 2.2' from the nucleus); however, the term has also been used for the entire jet, and for the nuclear jet. What in the literature is referred to as the core is strongly dependent on the observing frequency and resolution.

Centaurus A in will be one of the key targets of the Cherenkov Telescope Array (CTA). With an 8° field of view, CTA will be able to cover the giant lobes in one exposure. Moreover, CTA will have the resolving power to see sub-structures in the inner regions of the radio galaxy, see CTA Observatory — Key Targets.

Position of the nucleus

The position of the nucleus, which is hidden in the optical by the dense dust lane, was eventually determined using the Hubble Space Telescope (HST) optical WFPC2 image combined with the HST near-infrared NICMOS image and the SOFI/NTT image. The derived position is marked on the following three images which show NGC 5128 with increasing resolution (see Marconi et al. 2000 and Kainulainen et al. 2009).

ESO: VLT — Kueyen
HST: WFPC2 mosaic
North is at the top, West is to the right.


  1. Alternative names:
    Name                   Type     Name                       Type
    =================      =======  ======================     ======
    1FGL J1325.6-4300      Gamma
    1322-427                        MCG -07-28-001             G
    1322-428                        Mills 13-4A
    13223-427                       MOST 1322-427
    1ES 1322-427           XrayS    MRC 1322-427               RadioS
    1H 1323-428            XrayS    MSH 13-4-02
    1Jy 1322-428                    NGC 5128                   G
    1Jy 1322-42                     NRL 7
    1M 1322-427                     PGC 046957                 G
    2A 1322-427                     PMN J1325-4302             RadioS
    2E 1322.5-4245                  PMNM 132221.3-424700       RadioS
    2EG J1324-4317                  PKS 1322-42                RadioS
    3EG J1324-4314                  PKS 1322-427
    3U 1322-42                      PKS 1322-428
    4U 1322-42                      PKS B1322-428              RadioS
    ARP 153                G        PKS J1325-4303             RadioS
    AM 1322-424            G        PRC C-45                   G
    Bennett 60                      RORF 1322-427
    Cen A                  RadioS   RX J132524.4-430100
    Centaurus A            RadioS   RX J1325.5-4301            XrayS
    CTA 59                          SGC 132233-4245.4          G
    Cul 1322-427           RadioS   SPB216
    Dunlop 482                      XRS QSO 3A 2E 3038
    EGRET J1326-43         G        [PT56] 27
    ESO 132233-4245.4      G        [VDD93] 184
    ESO 270-IG 009         G        [VV2000b] J132528.0-430100
    ESO-LV 2700090         G        [VV98b] J132528.0-430100
    GRO J1314-42                    [CRA98] 4
    H 1322-427                      [M98c] 132233.0-424524
    ICRF J132527.6-430108  RadioS   [KWP81] 1322-42            RadioS
    IERS B1322-427         RadioS   [A94] 35                   G
    IRAS  13225-4245       IrS
    IRAS F13225-4245       IrS
    LGG 344:[G93] 002      G

  2. Distance determinations:

    Currently, the most accepted distance value to the central regions is 3.8 ± 0.1 Mpc (see Harris et al. 2010).

    An overview of distance determinations is also available in the NASA/IPAC Extragalactic Database of Distances.

    From radial velocity measurements which give an average of 547 ± 5 km s-1, a redshift z of 0.00183 ± 0.00002 is derived (Graham 1978). While frequenty used, this would place Cen A at a distance of 7.7 Mpc! This redshift differs significantly from the calculated z value determined by other means. The discrepancy is due to the proximity of Cen A and a significant superposition of the proper motion of the galaxy within its group and its cosmological velocity.
    Other velocity measurements:
        538 km s-1 (Wilkinson et al. 1986; from spectroscopy, absorption line spectra)
        541 ± 7 km s-1 (Hui et al. 1995; from planetary nebulae)
        546 ± 7 km s-1 (Woodley et al. 2007; from globular clusters)
        539 km s-1 (Walsh et al. 2015; from planetary nebulae)

    Regarding the large radio galaxy scale, Wykes et al. (2015b) remark that "The distance to the giant lobes is not well constrained; HI absorption against the south-west inner lobe and higher radio linear polarisation of the northern inner lobe could hint at the northern giant lobe in front (van Gorkom et al. 1990; Junkes et al. 1993). The absence of a depolarisation signal in the 1.4 and 5 GHz radio continuum data at the position of the dwarf irregular galaxy ESO 324—G024 (which is in projection on the northern giant lobe and at approximately the same distance as Centaurus A's core) also favours the northern giant lobe being in front (Johnson et al. 2015). In turn, the southern giant lobe is both larger in projection and brighter (e.g. Alvarez et al. 2010; Abdo et al. 2010; Feain et al. 2011), which would suggest the southern giant lobe being closer if disregarding different physical conditions in the lobes."

  3. Black hole mass estimates:

    Currently, the most accepted black hole mass is (5.5 ± 3.0) x 107 Msun (Cappellari et al. 2009).

    A review paper on the black hole mass comparing the different techniques and results is by Neumayer (2010).

    Note by S. Wykes: "The existence of a binary black hole has been disfavoured based on stellar and gas kinematics, which show no sign of disturbance by a second black hole, and on the fact that there is only a single radio- and K-band source at the nucleus (N. Neumayer, private communication)."

  4. Age estimates:

    Age of the parent elliptical galaxy:

      We can only measure the age of stars and globular clusters; it is more difficult to determine how old the elliptical galaxy is itself.
      Rejkuba et al. (2011) measured stellar age distribution, finding that bulk of the stars in this galaxy has formed 12 ± 1 Gyr ago in an intense and short starburst event. According to that, > 80 per cent of the mass of the galaxy would have formed by approximately 11 Gyr ago. However, we can't be certain that this is the elliptical we see today. Are these stars otherwise coming from mergers of several galaxies that assembled hierarchically to build the elliptical we see today? (See Section Stellar content for more details.)

    Radiative age of the radio galaxy:

    • ∼ 30 Myr  (Hardcastle et al. 2009; based on synchrotron ageing fitting)
    • ≤ 80 Myr  (Yang et al. 2012; reasoning that ages significantly higher are not consistent with the observations of gamma-ray inverse-Compton emission)

    Dynamical age (true age, physical age) of the radio galaxy:

  5. Jet inclination estimates:

    • 73° ± 3°  (Graham 1979; relying on H II regions)
    • 72° ± 3°  (Dufour et al. 1979; relying on disc of young stars and H II regions)
    • 61° ± 5°  (Skibo et al. 1994; based on OSSE measurements and model)
    • 60° — 77°  (Jones et al. 1996; from jet/counterjet radio brightness ratio; parsec scale)
    • 50° — 80°  (Tingay et al. 1998b; from jet/counterjet radio brightness ratio; parsec scale)
    • ≤ 50°, preferably ~ 15°  (Hardcastle et al. 2003; from jet/counterjet radio brightness ratio and component speeds; kiloparsec scale)
    • 12° — 45°  (Müller et al. 2014; from jet/counterjet radio brightness ratio and component speeds; parsec scale)
    • ~ 50°  (Wykes et al. 2019; results from the 1D fluid model of the jet consistent with inclination of 50°; kiloparsec scale)

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