J/A+A/327/952 Centaurus cluster velocities (Stein+ 1997)
Velocity structure of the dwarf galaxy population in the Centaurus cluster
Stein P., Jerjen H., Federspiel M.
<Astron. Astrophys. 327, 952 (1997)>
=1997A&A...327..952S 1997A&A...327..952S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radial velocities
Keywords: clusters of galaxies: general: Centaurus cluster - evolution of -
galaxies: redshifts; evolution; NGC 4696
Abstract:
Based on the photometric survey of the inner region of the Centaurus
cluster (Jerjen & Dressler, 1997, Cat. J/A+AS/124/1) we measured
redshifts for a deep, surface brightness limited sample of galaxies
using the MEFOS multifibre spectrograph at the ESO 3.6m telescope.
With the new data set radial velocities for 120 centrally located
cluster members become available which is equivalent to 78% of all
known cluster galaxies in the region brighter than BT=18.5. The
relevant aspect of this investigation is that new redshifts for 32
dwarf galaxies have been measured, rising the total number to 48. We
investigate the prominent bimodal velocity distribution of Centaurus
in more detail, discussing the very different characteristics of the
velocity distributions for the main Hubble types E&S0, spirals,
Im&BCD, and dE&dS0. The nucleated, bright dwarf ellipticals are the
only galaxies with a Gaussian-like distribution centred at
3148±98km/s. The remarkable coincidence of this velocity with the
mean velocity of Cen 30 and the redshift of NGC 4696 in particular
strongly suggests a connection of the dE&dS0s to the gravitational
centre of the Centaurus cluster and/or to the cluster dominant E
galaxy. The application of statistical tests reveals the existence of
a population dwarf galaxies bound to NGC 4696. The dynamical
parameters for the two velocity components suggest that Cen 30 is the
real Centaurus cluster whereas Cen 45 can only be a loosely bound
group of galaxies. This conclusion is followed up with a type-mixture
analysis. All results are fully consistent with the cluster-group
scenario. Whether Cen 45 is merging with the cluster or is located in
the close background remains unclear. We show that the poorness of Cen
45 represents an intrinsic problem which makes it difficult to
approach this question.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5a.dat 81 36 New redshifts for Centaurus cluster members
table5b.dat 81 14 New redshifts of background galaxies
table5c.dat 81 65 Reobserved redshifts for Centaurus cluster members
table5.tex 97 283 LaTeX version of table5
table5.ps 83 931 PostScript version of table5
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See also:
J/A+AS/124/1 : The Centaurus Cluster Catalogue (Jerjen+ 1997)
Byte-by-byte Description of file: table5?.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Sequential number
5- 6 I2 h RAh Right ascension (1950.0)
8- 9 I2 min RAm Right ascension (1950.0)
11- 15 F5.2 s RAs Right ascension (1950.0)
17 A1 --- DE- Declination sign
18- 19 I2 deg DEd Declination (1950.0)
21- 22 I2 arcmin DEm Declination (1950.0)
24- 27 F4.1 arcsec DEs Declination (1950.0)
29- 31 I3 --- CCC Centaurus Cluster Catalogue (Jerjen & Dressler
1996, Cat. J/A+AS/124/1) reference number
33- 38 A6 --- Mtype Morphological type
40- 44 F5.2 mag BT Total blue magnitude
46- 49 F4.1 mag/arcsec+2 SBeff ? Effective surface brightness
51- 54 F4.2 % Prob ? Cen 45 cluster member probability (1)
56- 60 I5 km/s Vcc ? Cross-correlation redshift
62- 63 I2 km/s e_Vcc ? rms uncertainty on Vcc
65- 69 I5 km/s Vem ? Emission line redshift
71- 72 I2 km/s e_Vem ? rms uncertainty on Vem
74- 78 I5 km/s cz ? Heliocentric radial velocity (2)
80- 81 I2 km/s e_cz ? rms uncertainty on cz
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Note (1): If prob=0.00, this automatically implies that the galaxy is
a 100% Cen 30 member.
Note (2): Weighted average of Vccf and Vemi.
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Acknowledgements: Martin Federspiel
(End) Patricia Bauer [CDS] 26-Jan-1998