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Notes for object NGC 5128

33 note(s) found in NED.

1. 2009ApJ...702.1127R
Re:NGC 5128
Centaurus A (NGC 5128) is a nearby Sy2 nucleus, with its core heavily obscured
by a dust lane. This makes it visible only at wavelengths longwards ~1 {mu}m
(Schreier et al. 1998; Marconi et al. 2000). Indeed, Hough et al. (1987),
Packham et al. (1996), and Marconi et al. (2000) determined a value for the
extinction caused by the dust lane of A_V_ ~ 7-8 mag. However, the total
obscuration on our LOS to the core was estimated by Meisenheimer et al. (2007)
to be A_V_ ~ 14 mag, including the torus material. Due to the existence of the
dust lane, that is probably affecting our nuclear fluxes (specially the near-IR
ones), we exceptionally have taken this foreground extinction into account for
the fit of Centaurus A with the clumpy models (Figure 7), by fixing A_V_ = 8 mag
and applying the Calzetti et al. (2000) law to the fitted models.
The clumpy models reproduce the observed photometry very accurately, but not
the broad absorption silicate feature detected in mid-IR spectroscopy and
interferometry (Siebenmorgen et al. 2004a; Meisenheimer et al. 2007). This
mismatch in the fitted model could be due to the synchrotron radiation
contribution to the IR fluxes claimed by Bailey et al. (1986), Turner et al.
(1992), Chiaberge et al. (2001), and Meisenheimer et al. (2007). Indeed,
Meisenheimer et al. (2007) find from mid-IR interferometric observations that
the contribution of synchrotron emission to the nuclear emission of Centaurus A
is of ~80% at ~8 {mu}m and ~60% at ~13 {mu}m. However, the results of Radomski
et al. (2008), including the lack of variability at ~10 {mu}m (see Radomski et
al. 2008 and references therein) and zero polarization at ~1 mm (although low
millimeter polarization may be associated with low-luminosity sources; Packham
et al. 1996) are inconsistent with a synchrotron source as that suggested by
Meisenheimer et al. (20 07). A more detailed analysis of the SED of this galaxy,
e.g., including an optically thin power law in the fits to account for the
synchrotron radiation can be done. However, this kind of detailed analysis of an
individual galaxy is beyond the scope of this work.
The probability distributions derived from the fit of the Centaurus A SED
with the clumpy models clearly constrain the number of clouds N_0_, the optical
depth of each cloud {tau}_V_, and the width of the angular distribution {sigma}.
N_0_ resembles a Gaussian distribution centered at the median value N_0_ = 2 +/-
1. The {tau}_V_ histogram shows an asymmetric shape, with a tail toward low
values and of median {tau}_V_ = 176 at a 68% confidence level. High-{sigma}
values are more probable than others (median value of 58^deg^ +/- ^10^_15_),
and the same for the inclination angle of the torus (i > 85^deg^). In
contrast, low values of q are preferred (q < 0.2). The radial thickness of the
torus Y has been introduced to the code as a Gaussian prior centered in 15 with
a width of 2.5, as explained in Section 4.2. Indeed, the preliminary fit of
Centaurus A without restrictions in any of the model parameters was the only one
that constrained the radial thickness of the torus, with a median value of its
probability distribution of Y~ 15. The calculated median value of the optical
extinction produced by the torus is A^LOS^_V_ = 300+/-^100^_80_ mag for this

2. 2009ApJ...696.1218Z
Re:NGC 5128
Centaurus A (NGC 5128) is a well-known, near-by (3.4 Mpc) FRI radio galaxy. Its
nuclear activity is manifested by large radio/X-ray jets-radio plumes extending
to 250 kpc, and a compact circumnuclear disk. The multiwavelength variability of
the nucleus, its polarization, and ionization of the optical filaments suggest
that Cen A contains a misaligned BL Lac/blazar nucleus (Israel 1998). Rothschild
et al. (2006) report a 2-10 keV X-ray flux which varies between 1.69 and 3.23 *
10^-10^ erg s^-1^ cm^-2^ in six observations between 1996 August and 2004
February with the PCU2 instrument on Rossi X-ray Timing Explorer RXTE.

3. 2009ApJ...690.1322W
Re:Centaurus A
Cen A. Cen A recently underwent a galaxy merger. The X-ray spectrum is extremely
complicated, as presented in (Evans et al. 2004). Due to the complex form, we do
not include an analysis of this source.

4. 2008MNRAS.386.2242H
Re:NGC 5128
NGC 5128 - The distance (D= 3.5 Mpc) and black hole mass (M_bh_=
4.5^+0.6^_-0.4_ x 10^7^ M_sun_) are taken from Neumayer et al. (2007),
we estimate the 1{sigma} black hole mass error according to their fig.
12. This black hole mass is consistent with the result of
Haring-Neumayer et al. (2006), M_bh_= 6.1^+0.6^_-0.8_ x 10^7^ M_sun_.

5. 2008MNRAS.386.2242H
Re:NGC 5128
NGC 5128 - The distance (D= 3.5 Mpc) and black hole mass (M_bh_=
4.5^+0.6^_-0.4_* 10^7^ M_{sun}_) are taken from Neumayer et al.(2007), we
estimate the 1{sigma} black hole mass error according to their fig. 12. This
black hole mass is consistent with the result of Haring-Neumayer et al. (2006),
M_bh_=6.1^+0.6^_-0.8_*10^7^ M_{sun}_.

6. 2008A&A...484..341R
Re:NGC 5128
Figure A.4. Centaurus A, the closest active radio galaxy. The 11.9 micron image
shows an unresolved central core, with extended emission at 10% level. The 8.6
micron image shows an unresolved core. For comparison, see Siebenmorgen et al.
(2004) for a 10.4 micron image showing an unresolved core of less than 0.5".

7. 2007A&A...461.1209D
Re:Centaurus A
Centaurus A: The BeppoSAX observations of the source were published in
Grandi et al. (2003). The authors studied the variability properties of
the source and summed the five BeppoSAX observations to precisely model
the X-ray spectrum. The results presented here are, overall, in
agreement with the results presented in Grandi et al. (2003). Also,
Risaliti (2002) presented these observations finding results that are
very similar to the ones reported in this work.

8. 2006ApJ...642...96E
Re:Centaurus A
The nucleus of Centaurus A has been analyzed in detail by us (Evans et al.
2004), and this work should be consulted for a detailed description. The nuclear
spectrum is well described by a heavily absorbed (N_H_ ~ 10^23^ atoms cm^-2^)
power law of photon index 1.7, accompanied by a narrow fluorescent Fe K{alpha}
emission line of equivalent width 60+/-15 eV. In addition, Evans et al. (2004)
find that a contribution from a softer power law, related to the parsec-scale
VLBI jet, is necessary to model the nuclear continuum.

9. 2006ApJ...638..642B
Re:Centaurus A
Cen A - This Seyfert 2 (z = 0.0018) is one of the brightest objects in the
sample. The statistics allow us in this case to determine the
intercalibration factors between JEM-X, ISGRI, and SPI (1.0 :
0.92^+0.04^_-0.04_ : 1.10^+0.06^_-0.06_). An absorbed power-law plus a
Gaussian line gives the best fit to the data with N_H_ = 14.6^+1.4^_-1.4_
x 10^22^ cm^-2^, GAMMA = 1.96, and an equivalent width of the iron Kalpha
line of EW = 108 eV. Adding an exponential cutoff does not improve the fit
(E_C_ = 870^+3810^_-410_ keV). The results are consistent with results
published on a subset of INTEGRAL data and with BeppoSAX data (Soldi et
al. 2005).

10. 2006AJ....131..114B
Re:MRC 1322-427
MRC B1322-427: Well-studied low-luminosity radio source
Centaurus A, the nearest radio galaxy, reviewed by Ebneter &
Balick (1983) and Israel (1998). The optical counterpart is the
dust-lane elliptical galaxy NGC 5128.

11. 2005ApJS..157...59L
Re:NGC 5128
NGC 5128 (Centarus A) is a peculiar lenticular galaxy at a distance of 4.21 Mpc
with a warped lane of gas and dust. It is also a bright radio galaxy with an
X-ray jet. ULX1 (IXO 76) is located on the edge of the bulge. This ULX showed
luminosities ~8 * 10^39^ ergs s^-1^ in five observations in a 10 day time
window, but it was below 0.2 * 10^39^ ergs s^-1^ in the other three observations
over 8 years.

12. 2005A&A...440...73C
Re:NGC 5128
NGC 5128: the fit has been performed on a dust-corrected image kindly provided
by A. Marconi, obtained combining H and K band HST images of this source. The
central 1" is flagged due to the presence of a strong point source.

13. 2002ApJ...574..740T
Re:NGC 5128
NGC 5128 has a mass estimate from ground-based observations of a
rotating gas disk (Marconi et al. 2001) but no HST spectroscopy;
moreover, the galaxy has peculiar morphology, presumably because
of a recent merger, and thus may not follow the same M_BH_-{sigma}
relation as more normal galaxies.

14. 2002ApJ...573..306E
Re:NGC 5128
NGC 5128
We report measurements of the radio-bright center of NGC 5128 (Cen A)
at 6 and 2 cm. The integrated fluxes are 6.1 and 0.38 Jy at 6 and 2 cm,
respectively, and the resulting spectral index is {alpha}^6^_2_ = -2.5.

15. 2001A&A...378...51B
Re:NGC 5128
NGC 5128 (Centaurus A): Molecular gas was recently detected by
Charmandaris et al. (2000) in the gaseous shells of Centaurus A, a galaxy
which also contains several stellar shells. It is widely accepted that
the formation mechanism for stellar shells can result from a minor merger
(Quinn 1984; Dupraz & Combes 1987) while the details of the dynamical
behavior of the gaseous component in minor mergers is still an open issue.
Since TDGs seem to form as a result of major interactions/mergers and
Centaurus A is a rather unique object so far, we do not include it in our

16. 2000ApJS..131...95F
Re:VSOP J1325-4301
J1325-4301 (Cen A). - Our image, limited by the short observing time,
shows symmetrical structure elongated in the northeast-southwest direction.
Other details of this source are unreliable. High dynamic range images of
this source are published by Tingay et al. (1998).

17. 1999A&AS..136...35S
Re:NGC 5128
NGC 5128 -- The observations of six HII regions in the elliptical galaxy
Cen A (classified as Seyfert 2 in NED) by Mollenhoff (1981) revealed
several WR features in one region (#13) near the rim of the dust disk
of this well studied galaxy. Broad lines of N III {lambda}4640,
He II {lambda}4686, C III {lambda}4650, and C IV {lambda}5808 are
identified. According to Rosa & D'Odorico (1986), WR features are found
in two (including #13) out of six surveyed regions.

18. 1997A&A...319...33A
Re:NGC 5128
NGC5128 The 14.3 ks PSPC exposure of CenA in Fig. 14 shows two X-ray Sources of
C=28.5 and 5.3 at p.a. 45^deg^. The stronger source is at r_1_=30.2'. In the
opposite direction there is a source C=10.8 at p.a.=232^deg^ and r_2_=32.2'. It
is evident from Fig. 14 that the X-ray emission from the central regions of Cen
A is elongated along this same line. The line drawn in Fig. 14 is the line of
the X-ray jet from the center of the galaxy which is at p.a.=53^deg^ and the
X-ray counter jet at p.a.=227^deg^ (Feigelson et al. 1981). These inner X-ray
jets are in turn aligned with the inner radio jets in Cen A. The outer X-ray
isophotes from the ROSAT Survey extends strongly to the NE for about 5^deg^ and
less strongly to the SW for about 2^deg^ at p.a.=53^deg^ and 227^deg^ (Arp
1994a). As described in that referenced paper the SW X-ray extension leads
directly to the strong radio and X-ray galaxy NGC 5090.
It is clear that the major X-ray sources in this region lie fairly closely along
the line of the X-ray and radio jets coming from the nucleus of the galaxy. The
strongest X-ray source at C=28.5 actually appears extended along this line.
Optically identifications have only been attempted for the three strongest
sources in this field. The C=28.5 and 10.8 source could not be identified,
perhaps lending weight to the idea that they are actually extended. The C=15.6
source is identified with an m_J_=19.5 mag. BSO (see Table 3).

19. 1996ApJS..103...81C
Re:NGC 5128
NGC 5128.--Seyfert 2. Centaurus A. Polarization maps of the large-scale
structure at 4.75 GHz in Junkes et al. (1993). Scaled-array VLA maps of the
inner structure at 1.4, 1.6, and 4.9 GHz in Clarke, Burns, & Norman (1992).

20. 1996ApJ...459..100N
Re:EGRET J1326-43
J1326-43.--This error circle contains no known blazars, but 31' from the
center is Centaurus A = NGC 5128, an unusual radio galaxy with an X-ray jet
(Feigelson et al. 1981) and large radio lobes (Meier et al. 1989) located only
3.5 Mpc away (Hui et al. 1993). This identification must be tentative with
such a large error circle. Also, the diffuse emission in this region shows
some low-level structure not found in the model. Such irregularities might
disturb the position estimate or the significance of the detection. This
possible identification has not been mentioned in any previous list because
recent revisions of the Galactic diffuse model caused the source position to
shift. Other cataloged objects in the circle include several normal stars,
several normal galaxies, several IRAS infrared sources, the pulsar
PSR 1325-43, and the supernova SN 1986G. None of these shows any
characteristics that would make it likely to be a strong emitter of
high-energy gamma rays. Nice, Sayer, & Taylor (1994) searched part of the
error circle for new pulsars, but found none. It is plausible that Cen A could
be a high-energy gamma-ray source. It is the brightest extragalactic source of
hard X-rays near 100 keV, and its spectrum does not show the sharp high-energy
cutoff typical of Seyfert galaxies (Kinzer et al. 1995). The EGRET spectrum
extrapolates to match fairly well with the contemporaneous COMPTEL
measurements of Collmar et al. (1993) around 1 MeV. The spectral index would
have to steepen by ~1 between 100 keV and the EGRET energy range. This
gradual steepening is consistent with a nonthermal synchrotron/Compton model
of the emission (Grindlay 1975; Mushotzky et al. 1978; Beall & Rose 1980),
probably not with the Compton reflection model (Zdziarski et al. 1990; Skibo,
Dermer, & Kinzer 1994). The gamma-ray luminosity of 8.3 x 10^40^ ergs s^-1^ is
only a few hundred times that of our own Galaxy.

21. 1994CAG1..B...0000S
Re:NGC 5128
S0 + S pec
Hubble Atlas, p. 50
April 19/20, 1982
IIIaF + RG610
240 min
NGC 5128 is the first recognized and the most famous example of
the combination of a dust feature and an early-type galaxy, shown here
in a print made from a Las Campanas 100-inch plate taken by Monet on a
red emulsion. The galaxy is also illustrated in the Hubble Atlas,
where early literature references to the radio properties are given,
having become known just at the time of publication.
The elongation of the underlying old stellar population whose
major axis is perpendicular to the dust lane was recognized by Baade
and Minkowski (1954). It is well shown in a deep photograph printed to
optimum contrast in van den Bergh (1976b) and in Graham (1979). The
elongation is not well shown in the print here, neither in the insert
nor the main print. The luminosity of the stellar component in
Graham's reproduction (his Fig. 1) can be traced nearly to the right
border of the main print here. The major axis of the flattened image
of the underlying S0 form extends from the lower right to the upper
left on this print.

22. 1994CAG1..B...0000S
Re:NGC 5128
Hubble Atlas, p. 50
S0 + S pec
April 19/20, 1982
IIIaF + RG610
240 min
The print here is from the same plate by
Monet used for the print on the preceding page.
The orientation is north to the left, west at the
The faint outer diffuse surface light,
filamentary features, and the H II regions
discovered by Blanco et al. (1975) are as far
beyond the lower-left corner of the print as that
corner is from the center of the galaxy. The faint
outer isophotes traceable on van den Bergh's
(1976b) and on Graham's (1979) high-contrast
prints extend to a distance from the center equal
to the distance to the left and right borders of the
print here. The major axis of the flattened underlying
old-star population is from the lower left to
the upper right.
Much photometric and spectroscopic work
has been done since the early description of NGC
5128 was written in the Hubble Atlas. The rotation
of the dust lane was established by Burbidge
and Burbidge (1959a) and was confirmed and
the results extended by Graham (1979). The
kinematics are satisfied by a model in which the
dust lane is a disk whose front and back sides are
both visible and which is viewed at an angle that
is 17 deg from edge on. The disk is rotating such
that the northwest side of the disk (the upper-left
side of the dust lane here) is receding. The
maximum velocity difference between the northwest
and the southeast (lower right) ends of the disk
(the dust lane) is 700 km/s, corrected to what
would be observed edge on. This rotational
velocity, of course, is very high.
The rotation of the stellar component whose
major axis is at right angles to the dust was
finally established by Bertola, Galletta, and
Zeilinger (1985) in an impressive study. Their
measured rotational gradient of the old star
component was 2 km/s/arcsec in the sense that
the southwest side (upper right) is receding. The
maximum velocity difference in their measurements
between the southwest and the northeast
ends of their long slit placed along the major axis
of the stellar component is 160 km/s. This,
combined with their measured velocity dispersion
of 140 km/s, when placed in the velocity/dispersion
diagram of Illingworth (1977) and of
Binney (1978), show that the old stellar component
is a rapid rotator, similar to almost all S0
bulges (Dressler and Sandage 1983). (The result
shows almost certainly that the form of the old
stellar component of the galaxy is not prolate.)
The kinematic results of the Burbidges, of
Graham, and of Bertola, Galletta, and Zeilinger
establish, as in NGC 2685 and in NGC 5266 on
the preceding panel, the presence of two velocity
systems whose angular momentum axes are at
right angles to each other, as in polar-ring
galaxies (compare Schweizer, Whitmore, and
Rubin 1983).
The galaxy type of the old stellar component
is uncertain. The photometry of van den Bergh
(1976b) shows that the luminosity profile is that
of a typical elliptical over the central part of the
image. This, however, is true for most S0 bulges.
It is only in the outer envelope that the S0
characteristics appear. We leave the type as
Nevertheless, NGC 5128 and the other
galaxies on the preceding panel are so unusual
that, in general, they cannot be used as examples
to understand the normal S0 galaxy types. In
each case some special event may have taken
place. (Compare Kahn and Woltjer 1959; Tubbs
1980; Simonson 1982; van Albada, Kotanyi,
and Schwarzschild 1982; Steiman-Cameron and
Durisen 1982; others.)

23. 1994AJ....107...99R
Re:NGC 5128
C-45 = Cen A= NGC 5128. Cen A is well-known for its warped lane of gas
and dust, which exhibits complicated dynamics (Graham 1979, Bland et al.
1987, Nicholson et al. 1992). The H I spectrum is complicated by strong
absorption features associated with the Milky Way and with Cen A itself,
seen against its strong central continuum. Accordingly, the total H I
mass is highly uncertain at 7.8 x 10^8^ M_sun_ plus or minus 30%,
assuming a distance of 3.3 Mpc. With an optical size of over 25', it is
possible that some HI flux may lie outside even the GB 140' beam. VLA
mapping by van Gorkom et al. (1990) showed 3.1 x 10^8^ M_sun_ of gas,
suggesting that there is diffuse or extended emission that was missing
from the synthesis maps. Although owing to its proximity Cen A is bright
in the far-infrared, its intrinsic far-infrared luminosity is not
remarkable in our sample; furthermore, it is relatively gas-poor.

24. 1992ApJS...80..137J
Re:MRC 1322-427
The inner components of Centaurus A, a complex source
showing a core component plus two (inner) lobes with bent structure,
particularly in the north-east lobe. The MOST observation does not detect
the outer lobes since they extend over several degrees. Centaurus A is the
closest and hence one of the most widely-studied radio galaxies so only a
few references are given here. The outer lobes can be seen best in the
images of Cooper et al. (1965) and Haynes et al. (1983). The inner lobes
were mapped by Gardner & Whiteoak (1971), Cameron (1971), Slee (1977),
Christiansen et al. (1977), Schreier et al. (1981) and Slee
et al. (1983).
Dust-lane galaxy, 7.7 m,
NGC 5128, at 13 22 33 -42 45 24 (Lauberts 1982) at the radio core. This is a
famous source, one of the first extragalactic
radio sources identified (see Bolton et al. 1949).
z = 0.0018, Palumbo et al. (1983).

25. 1985SGC...C...0000C
Re:NGC 5128
Plate 1313r
Centaurus A.
Plate 1381
Faint outer extension to 55' in PA 25-30 deg.

26. 1982ESOU..C...0000L
Re:ESO 132233-4245.4
=ESO 270-IG 09
very peculiar
radio source
*absorption lane inclined 80 degrees to major axis

27. 1976RC2...C...0000d
Re:NGC 5128
= Arp 153
= Centaurus A
Description and Classification:
Ap. J., 140, 35, 1964.
P.A.S.P., 80, 129, 1968.
Ap. J. (Letters), 170, L7, 1971.
Bull. A.A.S., 3, 444, 1971.
Publ.N.A.R.O., 1, 251, 1963.
Lowell Obs. Bull., VI, No. 123, 1964.
Ap. J., 140, 44, 1964.
Ap. J. (Letters), 170, L7, 1971.
Ap. Let., 8, 57, 1971.
Atlas Gal. Austr., 1968.
Photometry (UBV):
Ap. J. (Letters), 170, L7, 1971.
Ap. J., 178, 25, 1972.
Photometry (Star Sequence near Galaxy):
Ark.f.Ast., 5, 249, 1969.
Photometry (I.R. 1-10 microns):
Ap. J. (Letters), 170, L7, 1971.
Ap. J. (Letters), 170, L15, 1971.
Ap. J. (Letters), 191, L19, 1974.
Nature, 224, 253, 1969.
Ap. J. (Letters), 170, L7, 1971.
Lowell Obs. Bull. VI, No. 123, 1964.
Mass Determination of faint nucleus.
Ap. J. (Letters), 170, L7, 1971.
HII Regions:
Zs. f. Ap., 51, 64, 1960.
Interferometry H{alpha}:
Nature, 224, 253, 1969.
Info. Bull. South. Hemisphere, No. 14, 32, 1969.
HI 21cm (absorption and emission):
Ap. J. (Letters), 161, L10, 1970.
Astrophys. Lett., 8, 57, 1971.
IAU Symp. 44, 12, 1972.
Astr. Ap., 31, 283, 1974.
Radio Observations:
Ap. J., 140, 44, 1964.
Ap. J., 147, 25, 1967.
Ap. J., 154, 423, 1968.
Ap. J., 157, 481, 1969.
Ap. J. (Letters), 170, L11, 1971.
Ap. J. (Letters), 194, L35, 1974.
Proc. A.S. Austr., 1, 229, 1969.
A.J., 76, 211, 1971.
M.N.R.A.S., 152, 439, 1971.
M.N.R.A.S., 169, 15P, 1974.
Nature, Phys. Sc., 245, 83, 1973.
Bull. A.A.S., 6, 441, 1974.
Ap. J. (Letters), 161, L1, 1970.
Ap. J. (Letters), 165, L49, 1971.
Ap. J. (Letters), 171, L45, 1972.
Ap. J. (letters), 173, L99, 1972.
Ap. J., 180, 715, 1973.
Ap. J., 183, 357, 1974.
Bull. A.A.S., 3, 444, 456, 1971.

28. 1964RC1...C...0000d
Re:NGC 5128
= Cen A
Radio source.
One of the most peculiar bright galaxies.
see Helwan 21. HB 898, 1935. and photo reference.
A.J., 68, 76, 1963.
H.B., 898, 1935.
M.N.R.A.S., 109, 98, 1949.
Ap. J., 119, 223, 1954.
Ap. J., 129, 272, 1959.
Zeit. fur Ap., 51, 64, 1960.
Handbuch der Phys., Vol.53, 267, 1959.
M.N.R.A.S., 109, 94, 1949.
Observatory, 78, 24, 1958.
IAU Symp., No. 4, 1955 (Cambridge U. Press, p.169, 1957).
Zeit. fur Ap., 51, 64, 1960.
A.J., 67, 271, 1962.
Rotation and Mass:
Ap. J., 129, 271, 1959.
Radio Emission:
Nature 164, 101, 1949.
Ap. J., 119, 123, 1954.
Ap. J., 125, 1, 1957.
Ap. J., 133, 322, 1961.
Austral. J. Phys., 6, 452, 1953.
Austral. J. Phys., 11, 517, 1958.
P.A.S.P., 72, 368, 1960.
Caltech Radio Obs., 4, 1959.
Caltech Radio Obs., 2, 1961.
IAU Symp., No. 4, 1955.

29. 1964ApJ...140...35M
Re:Centaurus A
No. 32.-From 48-inch plate by Minkowski, reduced to 4 X 5-inch positive. The
distance is that determined by Sersic (1960) . The radio source is discussed in
the text.

30. 1964ApJ...139..560M
Re:NGC 5128
b) NGC 5128
It has previously been found by Bracewell, Cooper, and Cousins (1962) that at
10-cm wavelength the NE. component of the inner double source associated with
NGC 5128 was 15 per cent polarized in P.A. 115^deg^. The present observations
show that both components are polarized. In particular, the SW. component has
4.5 times less polarized flux density and must be 5 per cent +/- 1 per cent
polarized at 2840 Mc/s. In Figure 2 we have plotted our observations of |Q| and
|U| for the central source, and attempted to fit models to them. The best fit
would appear to be a model having a diameter of 1.3' for the stronger NE.
component and considerably less than 1' for the weaker SE. component. Due to the
unequal intensities and the angle of inclination between their planes of
polarization, the |Q| curve refers essentially to the stronger source and is
relatively unaffected by the diameter of the weaker source. On the other hand,
the |U| curve is very sensitive to the diameter of the weaker SE. source. This
is illustrated by the dotted curve for |U| which refers to a model with both
components having a diameter of 1.3'.
The E.-W. diameters and the intensity ratio of the unpolarized regions have
been measured at 31 cm (Moffet 1962), 21 cm (Twiss, Carter, and Little 1960) and
9 cm (Little 1963). Over this frequency range the stronger source seems to have
a constant diameter of ~2.4' whereas the weaker source apparently changes from
this value at the lower frequencies to < 1.1' at the highest (Little 1963). The
diameter of the polarized region in the stronger source we find is 1.3',
approximately half that of the unpolarized. Even if the ratio of sizes were
nearer unity for the weaker source, it is not surprising that we find the
polarized region in it to be considerably smaller than 1'. It would be of great
interest to determine the size of the polarized region in the weaker source at a
lower frequency where the unpolarized diameters of the two components of the
double source are apparently more nearly equal.

31. 1961Hubbl.B...0000S
Re:NGC 5128
(E0 + Sb)?
May 23/24, 1952
103aD + CG3486
40 min
Enlarged 3.5X
NGC 5128 is one of the most peculiar objects in the sky.
The background resembles that of an E0 galaxy, but the
wide and highly opaque absorption lane across the center
is unique. The lane is much wider and more chaotic than
lanes in Sb and Sc galaxies seen on edge. For this aspect,
compare 5128 with NGC 4594 (pg. 24 of the Hubble Atlas) or
any of the galaxies on pg. 25.
NGC 5128 is a source of intense radio emission.
Observations by Mills show that the strongest emission
originates in the absorption band. Baade and Minkowski have
published negative prints of NGC 5128 which illustrate
both the position of the strong radio source and the
features of the dust lane. Bolton, Westfold, Stanley, and
Slee (Austr. J. Phys., 7, 96, 1954) found that, in addition
to the strong radio radiation of the dust lane, a weaker
radiation comes from a nearly circular area 2 degrees in diameter
centered on NGC 5128. This area is larger than that in which
the optical radiation has yet been traced. The most recent
summary of the radio work on NGC 5128 is given by C. A. Shain
in the volume of the Paris Symposium on Radio Astronomy, 1958.

32. 1961Hubbl.B...0000S
Re:NGC 5128
Baade and Minkowski believe that NGC 5128 is two
galaxies in collision. The geometry of the situation is not
completely clear. Several points in the illustration help
in the interpretation. The background luminosity of that
part of the image on the northwest side of the absorption
lane is smooth, with no dust patches superposed. The
surface on the opposite side of the dust lane is covered
with a patchy pattern of obscuration. This pattern could
be reproduced if the dust were in a thin plane of an Sb or
Sc galaxy like NGC 0253 (pg. 34 of the Hubble Atlas), for
example. If this plane were tipped about 20 degrees to the
line of sight with the rotational axis coming out of the
paper, the observer would see part of this plane superposed
on the background of the E0 galaxy but only on the upper half.
The lower half of the E0 galaxy would be completely free of
the image of the Sb and would therefore show no absorption
patches. If the background E0 galaxy were removed we might
expect to see an image somewhat like that of NGC 7331
(pg. 17) or possibly NGC 4216 (pg. 25) at a slightly greater
angle. The absorption lane across NGC 5128 is very wide and
does not resemble that in NGC 7331. There may be two reasons
for this. The first is a geometrical one, the second dynamical.
(1) If we really see a dusty Sb or Sc superposed on an E0,
the dust lanes are not expected to look like those of a normal
galaxy such as NGC 7331 because there is an intense background
radiation field (the E0) upon which the dust of the Sb or Sc
can be silhouetted. Any dust present will be much more conspicuous
than normally. (2) If an actual collision is taking place,
some of the kinetic energy of the center of mass of the galaxies
may be transferred to the contents of the galaxies, in particular
to the gas and dust. If part of the energy is pumped into the
dust layer, this layer will become more distended against
the gravitational potential due to the galaxy as a whole
and the lane will appear to be wider and more disorganized
than in normal Sb or Sc systems.
J. L. Sersic has obtained isophotal contours of NGC 5128.
He describes the appearance of the image and gives absorption
data in Observatory, 78, 24, 1958. He states that "the central
region of the band (dark lane), which is more conspicuous in
the red light, presents a complex structure formed of chains
of condensations -- probably chains of high-luminosity O-B stars
-- separated by lanes of obscuring matter." He assigns an
apparent magnitude to the stars in the chains as m(pg) = 18.7.
There is no evidence whatsoever on PH-161-Mi for chains of
stars in the bright region of the central dust lane. Rather,
the texture of the luminosity is smooth. Dust lanes are
interspersed, but the luminous matter is not broken into
knots or condensations.

33. 1961AJ.....66..562V
Re:NGC 5128
5128 Dark patches and bright knots. Similar to NGC 1316 and NGC 1275?

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