J/ApJ/449/592 NGC 5128 PN. III. (Hui+ 1995)
The planetary nebula system and dynamics of NGC 5128.
III. Kinematics and halo mass distributions
Hui X., Ford H.C., Freeman K.C., Dopita M.A.
<Astrophys. J. 449, 592 (1995)>
=1995ApJ...449..592H 1995ApJ...449..592H (SIMBAD/NED BibCode)
ADC_Keywords: Planetary nebulae ; Radial velocities
Keywords: galaxies: abundances - galaxies: individual (NGC 5128) -
galaxies: kinematics and dynamics - galaxies: star clusters
Abstract:
We present a study of the halo dynamics and mass distributions of the
nearby giant elliptical galaxy NGC 5128 using planetary nebulae (PNs)
as test particles. Radial velocities of 433 PNs were obtained with
multifiber spectrographs on both the Anglo-Australian Telescope (AAT)
and the Cerro Tololo Inter-American Observatory (CTIO) 4m telescope.
The velocities were measured from the [O III]λ5007 emission
line with a typical 1σ error of ±4km/s and ±30km/s for the
AAT and the CTIO data, respectively. These PNs cover the entire galaxy
to a radius of 10kpc and extend along the photometric major axis out
to 20kpc. The PN velocity field shows the distinctive characteristics
of a triaxial potential: the galaxy's rotation axis is offset from its
photometric minor axis by 39±10deg; the rotation axis and the line
of maximum rotation are likely not orthogonal. We also find that the
ordered motions of the stars become more important with increasing
radius compared to their random motions. The rotation reaches
approximately 100km/s and 50km/s along the photometric major and minor
axes, giving a local V/σ ratio of about 1.0 and 0.5,
respectively. The aximuthal variation of the velocity dispersion
appears to be modulated by rotation, i.e., it reaches a maximum where
the largest rotation is observed and drops to a minimum at zero
rotation. The amplitude of this modulation is about 20km/s, compared
to a mean dispersion velocity of 110km/s. The kinematics of the
globular clusters depend on the metallicity. Taking [Fe/H]=-1.0 as the
dividing point, the metal-poor clusters do not show any significant
rotation. However the metal-rich clusters show both major and minor
axis rotation, and the amplitudes of the rotation are similar to that
of the PNs. The stellar velocity dispersion measured from
absorption-line spectra together with an Hα rotation curve of
the dust lane suggest that the stellar orbits are isotropic and the
mass-to-light ratio (M/LB) is 3.9 in the central region of the
galaxy. By applying the isotropic Jeans equation to the observed PN
major axis rotation and velocity dispersion, we show that the M/LB
increases with radius, suggesting the presence of dark matter in the
halo. Within a 25kpc radius, the total mass of the galaxy is
3.1x1011M☉ and M/LB=10. The rotation velocity of the
recently detected H I ring at a radius of 15kpc confirms our mass
model. The misalignment of the rotation axis relative to the
photometric minor axis, combined with the knowledge of the dust lane
orientation, allows us to uniquely determine the observer's viewing
direction. The true shape of the galaxy is nearly spherical yet
sufficiently triaxial to impose a distinctive gravitational signature
on the kinematics.
Objects:
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RA (2000) DE Designation(s)
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13 25 29 -43 01.0 NGC 5128
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5 54 433 NGC 5128 planetary nebula velocity catalog
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See also:
J/ApJS/88/423 : NGC 5128 PN. II. (Hui+ 1993)
Byte-by-byte Description of file: table5
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID PN identification number (see PN II)
7- 9 I3 km/s RV PN radial velocity
11- 16 F6.3 arcmin Rad Galactic radius (Distance from center of galaxy)
18- 24 F7.3 pix Xpos Photometric major axis distance (1)
26- 32 F7.3 pix Ypos Photometric minor axis distance (1)
34- 38 F5.2 mag m5007 PN [O III]λ5007 magnitude
(m5007 = -2.5log(F5007) -13.74)
40- 43 I4 --- Count ? Total analog-to-digital counts in the
[O III]λ5007 line
45- 48 F4.1 0.1nm FWHM ? FWHM of the line
50- 54 A5 --- Run Run (2)
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Note (1): Xpos positive to the northeast, Ypos positive to the northwest
The Galactic centre is assumed at
RA(2000.0)=13h 25m 277.72s, DE(2000.0)=-43deg 01' 5.8"
and the photometric major axis at P.A.=35deg.
Note (2): 1: 1987 AAT run
2: 1989 AAT run
3: 1989 CTIO run
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History: Prepared via OCR at CDS.
References:
Hui et al., Paper I (Planetary nebulae as standard candles) 1993ApJ...414..463H 1993ApJ...414..463H
Hui et al., Paper II (A planetary nebula catalog) 1993ApJS...88..423H 1993ApJS...88..423H
(End) James Marcout, Patricia Bauer [CDS] 07-Mar-1997