Facts

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

Cen A by Capella Obs.
Image: Capella Observatory: Josef Pöpsel, Stefan Binnewies; 2006-05-03

Coordinates (nucleus) :

R.A. (J2000) = 13h25m27.s6152 (201.o3650633)
Decl. (J2000) = -43o01'08."805 (-43o0191125)
lII = 309.o5158743
bII = 19.o4173247

Distance : 3.8 ± 0.1 Mpc 2)

1' = 1.1 kpc (at 3.8 Mpc)
z = 0.0006   (H0 = 50 km s-1 Mpc-1; q0 = 0.5)

Apparent Magnitude : mB = 7.96, mV = 6.98

Cen A Location
All-Sky Milky Way panorama (credit: Axel Mellinger)
with the location of Cen A

Constellation Centaurus and the position of Cen A (NGC 5128) (in Wikipedia)

A movie zooming into the heart of Cen A


NED query results as of 2009-12-02. (Link to NED)

SIMBAD query results as of 2009-12-02. (Link to SIMBAD)

HEASARC query results as of 2009-12-02. (Link to HEASARC)

TeV Catalog

General Description

(for a review see Israel (1998))

The elliptical (S0) galaxy NGC 5128 is the stellar body of the giant double radio source Centaurus A. It is one example of the family of elliptical galaxies that have an absorbing band of gas and dust projected across their stellar body. The prominent twisted disk of gas and dust contains many H II regions and is lying approximately along the galaxy minor axis, obscuring the nucleus at optical wavelengths. (This dust lane's rotation was determined by Burbidge and Burbidge (1962) in a way, that the south-east side is approaching and the north-west side is receding.)
The dust lane and the extended shell structures detected in long exposure optical images (Malin et al. 1983) are thought to be remnants of a recent (107 - 108 years ago) merger of a giant elliptical galaxy with a smaller spiral galaxy. A consistent modelling of this event as galaxy shredding, that includes two other 'peculiar' objects in the vicinity of Cen A, is given by Thomson (1992).
The giant double radio source Centaurus A which extends 10o on the sky can be resolved down to sub-arcsecond resolution in the inner radio structures which corresponds to several pc only due to it's proximity. A detailed description of the radio morphology is given in Meier et al. (1989).
Cen A as an active galaxy is usually classified 3) as a FR I type radio galaxy, as a Seyfert 2 object in the optical (Dermer & Gehrels 1995), and as a "misdirected" BL Lac type AGN at higher energies (Morganti et al. 1992). It is one of the best examples of a radio-loud AGN viewed from the side ( ~ 70o) 4) of the jet axis ( Graham 1979; Dufour et al. 1979; Jones et al. 1996). Its proximity of < 4 Mpc ( Harris et al. 1984; Hui et al. 1993) makes it uniquely observable among such objects, even though its bolometric luminosity is not large by AGN standards.
The supermassive black hole at the center of the active galaxy has an estimated mass between 104 and 108 solar masses (Israel (1998)) with recent results pointing more towards few 107 to 108 solar masses (Axon (2000), Marconi et al. (2000), Marconi et al. (2001), Silge et al. (2005), Cappellari et al. (2009)).
Radio observations revealed the huge lobes, which extend to an apparent diameter of 10o on the sky, optical observations showed filaments related to the inner jet seen in the radio and X-ray regimes, and X-ray observations detected flux variations on timescales of days. Cen A is one of the few detected MeV gamma-ray emitting AGN and it has been observed in gamma-rays intensively by the Compton Gamma Ray Observatory (CGRO) (see section on observations).

Historically, Cen A has exhibited greater than an order of magnitude X-ray intensity variability (Bond et al. 1996) with an intensity-independent spectral shape below about 100 keV. Most measurements, when fitted with models including a spectral break, show no distinct change of the spectral index (alpha ~ 1.7 - 1.8) below the break (i.e. at lower energies than ~ 100 keV) when the intensity changes (e.g. Baity et al. 1981, Feigelson et al. 1981, Morini et al. 1989, Maisack et al. 1992, Jourdain et al. 1993). A very early detection made during a short rocket flight (Lampton et al. 1972) measured a very hard X-ray spectrum with a power-law index of 1.0 . In gamma-rays, Cen A has been observed in the past by various instruments and has been found to exhibit states of high intensity as well ( Bond et al. 1996, Kinzer et al. 1995, Steinle et al. 1998).

The detection of a bright X-ray transient close (2'.5) to the nucleus of Cen A in ROSAT images taken in 1995 (Steinle et al. 2000) may shed new light on reported variability if measured with instruments with low spatial resolution.

The inner part of Cen A shows a circumnuclear disk of about 400 pc diameter and a central cavity of about 90 pc. This disk is emitting in the (sub) millimeter range. Against this emission, a variety of molecular absorption lines are seen (Israel et al. 1990).
In addition, evidence for a 40 parsec diameter disk (2.5") of thin ionized gas centered on the nucleus of Centaurus A has been found in the light of PA-alpha using the NICMOS instrument on board HST (Schreier et al. 1998). This disk is not perpendicular to the jet and thus it is not the accretion disk of the black hole.

Narrow emission lines in the (sub) millimeter regime originate in the dust band that crosses the optical picture of Cen A (Eckart et al. 1990). (This dust lane is not to be confused with the circumnuclear dust disk!)

     schematic view of an AGN

Cen A Poster in A3 format showing the relative sizes of features in various wavelength bands (in german):
     postscript (3.6 MB),
     pdf (140 kB)

Nomenclature of the (Radio) Structures

As in the literature often the radio structure elements are used to describe the position of the features discussed, here is a coarse description of the large scale features cited from Alvarez et al. 2000:

Cen A "... is an extended, complex and fairly symmetric source that exhibits two Giant Outer Lobes (GLs), the northern one (GLN) and the southern one (GLS), that span declinations between approximately -38° and -48°.

Closer to the center are two smaller Inner Lobes (ILs), situated to the northeast and southwest of the center, which we will designate as ILNE and ILSW, respectively.

Approximately to the north of the ILNE is the Northern Middle Lobe, which has no symmetric counterpart in the south.

The large feature between approximately -38° and -40° has been called the Northern Loop in the literature (Junkes et al. 1993).

In the nuclear region are the nucleus, the jet, the counter jet and the knots.

Some authors refer to the ILs plus the region closer to the center as the central source or as the central component. Also some authors refer to the GLs as the extended source or simply as the outer lobes.

Good descriptions on Cen A morphology are found in Burns et al. (1983) and in the review by Israel (1998).


Smoothed 4.57 GHz map of the whole radio structure of Cen A from Alvarez et al. 2000 (Fig. 1) with regions indicated.
North is to the top, East to the left of the picture.
The northern lobes and the jet are generally believed to tilted towards the observer i.e. the nothern part of Cen A is closer to the observer (Burns et al. (1983), van Gorkom et al. (1990), Junkes et al. (1993), Schreier et al. (1996), Israel (1998)).

The morphological definitions used in this web pages are as follows:
  1. the Whole Source is Cen A in its entire extension,
  2. the Inner Lobes (ILs) follow the usual definition, where ILNE indicates the inner lobe in the NE direction and ILSW in the SW direction, respectively,
  3. the region internal to the ILs will be called Nuclear Region (NR),
  4. the NR plus the ILs will be designated as the Central Region (CR),
  5. the Giant Northern Lobe (GLN) comprises the region north of the center (δ ∼ -42.45°) less the corresponding part of the CR; thus the GLN includes the Northern Middle Lobe and the Northern Loop,
  6. the Giant Southern Lobe (GLS) comprises the region south of the center less the corresponding part of the CR.

Details of the inner structures from the review of Israel (1998). (Fig. 3) 		Cen A APEX
multicolor composite including APEX (870 µm) data
ESO press release 2009-01-28

Position of the Nucleus

The position of the nucleus, which is hidden in the optical by the dense dust lane, was determined finally 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
HST: WFPC2
North is at the top, West is to the right.

Spectral Energy Distribution (SED)

SED including all data in the NASA/IPAC EXTRAGALACTIC DATABASE and recent H.E.S.S. data:

Cen A SED
New: the SED data from CGRO are listed in section "CGRO data points" of the page Observations!


SED from contemporaneous data obtained during a campaign in July 1995
    (Steinle et al. 1999, Steinle 2001a, Steinle 2001b)
    (Note that an error in the ROSAT and EGRET data points has been corrected!)

Footnotes :

  1. other 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:

    In a recent review by Harris, Rejkuba, and Harris (2009) the derived best mean distance value is 3.8 ± 0.1 Mpc.

    In the folowing the history of distance measurements is scetched:


    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) a redshift z of 0.00183 ± 0.00002 is derived, which is often used. (This would place Cen A at a distance of 12 Mpc!)
    This redshift differs significantly from the calculated z value from the distance determined by other means. The discrepancy is due to the proximity of Cen A and the significant superposition of the proper motion of the galaxy within it's group and it's cosmological velocity. (see Graham (1978); NED)

  3. classifications:

  4. inclination angle jet/line-of-sight:



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