1 . The Stellar Populations of NGC5128

1. The Stellar Populations of NGC51281. The Stellar Populations of NGC5128

ESO Vitacura – Nov 2005 Dante Minniti

Field 3 (jet)Magellan 1


(Rejkuba et al. A&A 2003a,b)

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).


Follow up Magellanphotometry confirmsthe presence ofblue MS stars along the NGC5128 jet, with age logT~7.0 yr

Rejkuba et al. 2003ESO Vitacura – Nov 2005 Dante Minniti


Resolved Populations in NGC5128Resolved Populations in NGC5128

Found a small population of young stars.The wide RGB indicates a significant metallicity spread

(Rejkuba et al. 2002 A&A).

HaloShell

RGB Tip


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

2. Variable Stars in NGC51282. Variable Stars in NGC5128


Variable Stars in NGC5128Variable 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.


Good periods spanning 60 to 600 days, mostly LPVs – Miras(Rejkuba et al. A&A 2003a,b).




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.



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 = -3.46 logP + 28.96, and assuming m-MLMC = 18.50 DN5128 = 3.9 Mpc (Rejkuba 2003).


3. The Star Cluster System of Cen A


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.


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).



Selection of GCs

The globular clusters are resolved with ~1” seeing, allowing their discrimination from foreground MW stars.

Rej

kub

a 20

03

Comparative globular cluster luminosity functions

Similar luminosity distributions with the systems of GCs of the MW and M31:unimodal, same peak at Mv~-7.5, maybe larger magnitude dispersion.


The globular cluster colors are bimodal two different populations:

metal-rich and metal-poor globular clusters in NGC5128 (Rejkuba 2001, Peng et al. 2004)

NGC5128 globular cluster colors


Kinematics of the NGC5128

globular cluster system

Comparison with the PN kinematics

1. The GC and PN kinematics are similar

2. The NGC5128 halo is slowly rotating

3. The velocity dispersion is large4. Difference between metal-poor

and metal-rich GCs

Peng et al. 2003, 2004



Plus a lot of young and intermediate age clusters in the dust ring!

Population of star clusters

4. Globular Cluster Planetary Nebulae in NGC51284. Globular Cluster Planetary Nebulae in NGC5128


Globular Cluster Planetary NebulaeGlobular 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 ?



G292 G619

Magellan IB&C slit


NGC5128 - G619


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



Follow-up spectroscopy with the ESO VLT in service mode acquired in June 2002.

A 3rd GCPN candidate is discovered in the VLT data


1st GCPN


3rd GCPN

RV reveals that this is just a chance superposition with a MW dwarf star.


Why are they important?

1. Dark matter in Elliptical galaxy halos (Richtler et al. 2002)

2. GC and PNe abundances (Walsh et al. 1999)

3. PNe lifetimes (Pottasch 1984, Renzini 1999)

Extragalactic Globular Cluster PNeExtragalactic Globular Cluster PNe



The firstextragalactic

GCPN

(D. M

inni

ti &

M. R

ejku

ba, A

pJ 2

002)

5.Identification of X-Ray Point Sources in Cen A


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.

X-Ray Point Sources in NGC5128X-Ray Point Sources in NGC5128


CH

AN

DR

A im

age

s, 2

AC

IS p

oin

tings

(K

raft

et a

l, A

pJ

200

2)


• Jet towards one side• Point sources• Diffuse emission

X-ray sources in GCs are

extremely rare (Verbunt+ 1995,

A&A).

“Bright” sources are defined

with LX > 1035.5 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).

Globular Cluster X-Ray Sources: Globular Cluster X-Ray Sources: The MWThe MW


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).

Globular Cluster X-Ray Sources: Globular Cluster X-Ray Sources: Other GalaxiesOther Galaxies



1` = 1 kpc

7x7 kpc


1` = 1 kpc

7x7 kpc


1` = 1 kpc

7x7 kpc


1` = 1 kpc

7x7 kpc

RESULTS Kraft+ Us

AreaNXPS

NOPT

NGC

NStars

H

1500 sq.arcmin

246

17

9

8

---

50 sq.arcmin

97

52

30

10

9

Identification of X-Ray SourcesIdentification of X-Ray Sources

Vast improvement in the optical ID of X-ray point sources in NGC 5128. Several of the sources are associated with GCs. These GC

X-ray sources should be very bright LMXRBs (LX>1037 erg/sec).


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


30 X-Ray point sources in NGC5128 globular clusters

Why are they important?

1. Census of the X-ray point source population

2. Identification of new GCs

3. Accelerated dynamical evolution of GCs in gEs

4. Trend of Lx with galaxy luminosity



LMXRBs inNGC5128 GCs

(Min

niti,

Rej

kuba

& F

unes

200

3, A

pJ).

6. Searching for Binary Star Clusters in Cen A


CenCen

• 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, Cen.

• Three theories:

1. Nucleus of a stripped dwarf galaxy.

2. Self enrichment.

3. Merger of two clusters.



CTIO 4m H images

A Binary GC in NGC5128 ?A Binary GC in NGC5128 ?• The giant HII region Sersic 13 has LH = 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 S = 42 pc. Compare with

Rroche = 26 pc and Rtidal = 70-120 pc.

• The velocity difference is V = 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)

The Large Magellanic Cloud

R136 in 30 Doradus “The Tarantula Nebula”ESO Vitacura – Nov 2005 Dante Minniti

A Binary GC in NGC5128 ?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 Cen like globular cluster ?


(Minniti et al. 2004, ApJ, Villegas et al. 2005, A&A)

1. Stellar populations2. Variable Stars 3. Star Clusters 4. New GC PNe

5. X-Ray Sources6. Binary Clusters

7. Supermassive BH8. Inner structure


NGC 5128 - Centaurus A

Documents

1 . The Stellar Populations of NGC5128