1. 1. The Stellar Populations of NGC5128
ESO Vitacura – Nov Dante Minniti

2. Field 3 (jet) Magellan 1 (Rejkuba et al. A&A 2003a,b)
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3. Very young stars found in the NGC5128 halo, mostly along
the jet (Graham 1998, Mould et al. 2000, Rejkuba et al. 2002).
A disrupted dwarf or jet induced SF? cf. Alignment effect at
high-z (e.g. van Breugel et al. 2003). HI gas cloud reservoir
(Schiminovich et al. 1994, Oosterloo & Morganti 2005).
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4. the NGC5128 jet, with age logT~7.0 yr
Follow up Magellan
photometry confirms
the presence of
blue MS stars along
the NGC5128 jet, with age logT~7.0 yr
Rejkuba et al. 2003
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5. Resolved Populations in NGC5128
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6. Shell Halo Found a small population of young stars.
RGB Tip
Found a small population of young stars.
The wide RGB indicates a significant metallicity spread
(Rejkuba et al A&A).
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7. Stellar populations HST ACS CMDs (Rejkuba et al 2005)
The NGC5128 halo has:
Old populations dominate
No blue HB
Wide metallicity spread
<[Fe/H]> ~ -1
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8. 2. Variable Stars in NGC5128
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9. Variable Stars in NGC5128
20-24 epochs with VLT+ISAAC reaching K=23 (1200 d, from 99 to 02).
Discovery of 1758 luminous periodic variable stars in the NGC5128 halo.
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10. Variable Stars in NGC5128
Good periods spanning 60 to 600 days, mostly LPVs – Miras
(Rejkuba et al. A&A 2003a,b).
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11. Variable Stars in NGC5128 Period distribution Difference F1-F2?
Metal-rich MW globular cluster Miras: 140<P<310 days.
LMC-SMC Miras: 100<P<550 days.
P-distribution similar to the MW bulge in general, but 10% with P>500 days – intermediate-age AGB.
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12. Variable Stars in NGC5128
First observed Mira P-L relation beyond the Local Group.
Measured the distance using the RGB Tip, and the Mira P-L relation from Feast 1998: Ko = logP , and assuming m-MLMC = DN5128 = 3.9 Mpc (Rejkuba 2003).
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13. 3. The Star Cluster System of Cen A
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14. Population of globular clusters
There are only 155 globular clusters known in the Milky Way.
Large numbers of globular clusters are found in giant elliptical galaxies.
For example, the gE galaxy NGC5128 has 1700 GC in total (Kissler-Patig 1997). This GC system is 10x that of the Milky Way.
The study of large GC systems is important:
 for theories of galaxy formation and of globular cluster formation,
 for measuring the distance, and
 for the dynamics and estimates of the dark matter content.
ESO Vitacura – Nov Dante Minniti

15. Discovery of new NGC5128 globular clusters.
UV photometry shows a bimodal color distribution.
For the 1st time in an E galaxy construct a deep globular
cluster LF down to MV = -5 (Rejkuba 2001 A&A).
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16. Selection of GCs
The globular clusters are resolved with ~1” seeing, allowing their discrimination from foreground MW stars.
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17. Comparative globular cluster luminosity functions
Rejkuba 2003
Similar luminosity distributions with the systems of GCs of the MW and M31:
unimodal, same peak at Mv~-7.5, maybe larger magnitude dispersion.
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18. NGC5128 globular cluster colors
The globular cluster colors are bimodal  two different populations: metal-rich and metal-poor globular clusters in NGC (Rejkuba 2001, Peng et al. 2004)
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19. Kinematics of the NGC5128 globular cluster system
Comparison with the PN kinematics
The GC and PN kinematics are similar
The NGC5128 halo is slowly rotating
The velocity dispersion is large
Difference between metal-poor and metal-rich GCs
Peng et al. 2003, 2004
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20. Population of star clusters
Plus a lot of young and intermediate age clusters in the dust ring!
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21. 4. Globular Cluster Planetary Nebulae in NGC5128
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22. Globular Cluster Planetary Nebulae
GCPN are extremely rare (Jacoby et al. 1997).
There are only 4 GCPN known in the Milky Way, but stellar
evolution predicts a total of 16 GCPN in 150 GC.
Large numbers of GCPN should be found in other gE galaxies,
which have much larger GC systems.
For example, the NGC5128 has 1700 GC in total (Kissler-Patig
1997), so there should be 50 – 200 GCPN in total in NGC5128.
Where are they ?
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23. ESO Vitacura – Nov 2005 Dante Minniti

24. Magellan I
B&C slit
G G619
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25. NGC G619
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26. Substracting the spectrum of the comparison cluster gives
a typical planetary nebula spectrum (D. Minniti & M. Rejkuba, ApJ 2002)
[OIII] lines have F5007/F4959 ~ 3
F5007 = 6e-16 erg/sec/cm2/A
M5007 = 24.3
V[OIII] = 702 km/s
The spatial and velocity match rule out a background object
G619 spectrum – G292 spectrum
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27. Follow-up spectroscopy with the ESO VLT in service mode acquired in June 2002.
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28. A 3rd GCPN candidate is discovered in the VLT data
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29. 1st GCPN
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30. 3rd GCPN
RV reveals that this is just a chance superposition with a MW dwarf star.
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31. Extragalactic Globular Cluster PNe
Why are they important?
Dark matter in Elliptical galaxy halos (Richtler et al. 2002)
GC and PNe abundances (Walsh et al. 1999)
PNe lifetimes (Pottasch 1984, Renzini 1999)
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32. The first extragalactic GCPN (D. Minniti & M. Rejkuba, ApJ 2002)
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33. 5.Identification of X-Ray Point Sources in Cen A
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34. X-Ray Point Sources in NGC5128
Kraft et al. (ApJ 2002) detected 246 point sources with
LX [0.4-5 keV] > 2x1036 erg/sec in NGC5128.
Most should be X-ray binaries and SN remnants.
The sources with LX [0.4-5 keV] > 5x1037 erg/sec are much
more numerous than in our MW and M31.
For NS one needs an accretion rate of 10-8 Mo/yr.
The most luminous could be multiple sources (7-8 expected),
or BHs, or ??
Most sources are variable.
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35. CHANDRA images, 2 ACIS pointings
Jet towards one side
Point sources
Diffuse emission
CHANDRA images, 2 ACIS pointings
(Kraft et al, ApJ 2002)
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36. Globular Cluster X-Ray Sources: The MW
X-ray sources in GCs are extremely rare (Verbunt+ 1995, A&A).
“Bright” sources are defined with LX > erg/sec.
There are only 14 GC X-ray sources known in the 150 GCs of the Milky Way, and only 1 with LX > 1037 erg/sec.
In M31 there are 30 GC X-ray sources (Di Stefano+ 2002, ApJ).
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37. Globular Cluster X-Ray Sources: Other Galaxies
High luminosity X-ray point sources in distant galaxies are
supposed to be X-Ray binaries or SN remnants.
Large numbers of GC X-ray sources should be found in gE
galaxies, which have more populated GC systems.
For example, NGC5128 has 1700 GC in total, so there should
be 150 bright GC X-ray sources in NGC5128.
Only 9 were known (Kraft et al. 2002, ApJ).
We find 30, including 23 newly discovered globular clusters
(Minniti, Rejkuba & Funes 2003, ApJ).
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38. 1` = 1 kpc
7x7 kpc
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39. 1` = 1 kpc
7x7 kpc
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40. 1` = 1 kpc
7x7 kpc
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41. 1` = 1 kpc
7x7 kpc
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42. Identification of X-Ray Sources
RESULTS
Kraft+ Us
Area
NXPS
NOPT
NGC
NStars Ha
1500 sq.arcmin
246 17 9 8
---
50 sq.arcmin 97 52 30 10
Vast improvement in the optical ID of X-ray point sources in NGC Several of the sources are associated with GCs. These GC X-ray sources should be very bright LMXRBs (LX>1037 erg/sec).
ESO Vitacura – Nov Dante Minniti

43. Colors and magnitudes of GCs with X-ray sources  X-Ray point sources appear preferentially in red (metal-rich) globular clusters.  X-Ray point sources appear preferentially in bright (massive) globular clusters. Minniti et al. 2003
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44. 30 X-Ray point sources in NGC5128 globular clusters
Why are they important?
Census of the X-ray point source population
Identification of new GCs
Accelerated dynamical evolution of GCs in gEs
Trend of Lx with galaxy luminosity
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45. LMXRBs in NGC5128 GCs (Minniti, Rejkuba & Funes 2003, ApJ).
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46. 6. Searching for Binary Star Clusters in Cen A
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47. wCen
Some bright globular clusters in the Milky Way and M31 have composite populations.
For example, color-magnitude diagram studies find a range of metallicities-ages in the largest globular cluster of the MW, wCen.
Three theories:
Nucleus of a stripped dwarf galaxy.
Self enrichment.
Merger of two clusters.
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48. CTIO 4m Ha images
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49. A Binary GC in NGC5128 ?
The giant HII region Sersic 13 has LHa = 39.6 erg/s.
The spectra of the young clusters exhibit broad WR features like R136 in 30 Dor in the LMC.
The projected separation is DS = 42 pc. Compare with Rroche = 26 pc and Rtidal = pc.
The velocity difference is DV = 49+/-21 km/s. If bound, one expects Vorb = 10 km/s.
If they are a physical pair, they will merge in a short timescale comparable with Porb = 107 yr.
The optical magnitudes and spectra give M = 1-10x105 Mo.
(Minniti et al. 2004, ApJ, Villegas et al. 2005, A&A)
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50. The Large Magellanic Cloud
R136 in 30 Doradus “The Tarantula Nebula”
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51. A Binary GC in NGC5128 ?
The ionizing source of the giant HII region Sersic 13 appears to be a pair of massive clusters.
The luminosities and spectra of these young clusters are similar to R136 in 30 Dor.
The velocity difference is small enough to suggest a physical binary.
If they are bound, they will merge in a short timescale.
The progenitor of an wCen like globular cluster ?
(Minniti et al. 2004, ApJ, Villegas et al. 2005, A&A)
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52. NGC Centaurus A
1. Stellar populations 2. Variable Stars 3. Star Clusters 4. New GC PNe 5. X-Ray Sources 6. Binary Clusters 7. Supermassive BH 8. Inner structure
ESO Vitacura – Nov Dante Minniti