Extragalactic star clusters
 Star clusters are found for almost all galaxy types
 Either “Globulars” (far away from the disk/center)
or star forming regions (bright) observed
 Examples:
1. NGC 5128 (elliptical), about 1600 GCLs; Harris et al.,
2006, AJ, 132, 2187
2. NGC 628 (spiral), complete Young Cluster Population;
Adamo et al., 2017, ApJ, 841, 131
3. M31 (Andromeda Galaxy), 1200 GCLs; Galleti et al.,
2004, A&A, 416, 917
 Review: Brodie & Strader, 2006, ARA&A, 44, 193
Magellansche Wolken 2/26
6Degreesonthesky LMC
Magellansche Wolken 3/26
5.4DegreesontheSky
47 Tuc
SMC
4Arcminutes 30 Dor:
Star cluster in the
LMC
4850 listed star
clusters of the LMC
in Bitsakis et al.,
2017, ApJ, 845, 56
2741 listed star
clusters in the SMC
and the Magellanic
Bridge in Bica et al.,
2020, AJ, 159, 82
NGC 1866
LMC, age
about 100 Myr
NGC 2298
Milky Way,
age about
15 Gyr
Open clusters in the MCs have the same morphology as GCs
in the Milky Way (MW)
Magellansche Wolken 10/26
Distance and Reddening
 LMC:
 V – MV = 18.5 mag
 E(B – V) = 0.05 to 0.1 mag
 Distance about 50 kpc
 SMC:
 V – MV = 19.0 mag
 E(B – V) = 0.05 to 0.1 mag
 Distance about 60 kpc
 Intrinsic reddening up to 0.2 mag for “normal”
regions in the bulge
Magellansche Wolken 11/26
Characteristics
 Irregular Galaxies
 Disintegrate because of gravitational
interaction with the Milky Way (MW)
 Global elemental abundance is lower
than in the MW: -2 < [Fe/H] < -0.3 dex
 Total masses about 20 times lower than
in the MW
 Global magnetic field lower than in the
MW
Matteucci et al., 2002, A&A, 387, 861
7 pc
20 pc
Diameters comparable to the MW
Magellansche Wolken 21/26
Magellansche Wolken 14/26
 Impact for the study of star clusters in the
Magellanic Clouds
1. The diameters of star clusters are normally below 1’
2. The core regions are difficult to resolve
3. The distance is no free parameter any more
4. There are almost no “foreground objects”
5. The membership determination on a kinematical
basis is almost impossible, Gaia should get better
data
6. Star clusters are most suitable to perform “statistical
investigations”
Classification of Star Clusters
Reddening free
indices
You need integrated photometric observations with these four
filters to classify star clusters in the MCs. Also works with other
photometric systems, but you need a filter in the U region.
Integrated
colors
Searle et al., 1980, ApJ, 239, 803
young
old
Searle et al., 1980, ApJ, 239, 803
lower metallicity lower metallicity
Klassifikation von Sternhaufen
Searle et al., 1980, ApJ, 239, 803
Seven “regions”
For LMC (full
circles) and SMC
(open circles)
Age: I, II and III
Age and Metallicity:
IV - VII
Bica et al., 1996, ApJS, 102, 57
Integrated colors
of 624 Star Clusters
in the LMC
Each “region” can
be calibrated in
terms of the age
and the metallicity
Here is an example
of Johnson UBV
photometry and not
Gunn uvgr
Bica et al., 1996, ApJS, 102, 57
M and m, semimajor and semiminor axis
PA positional angle of M, North = 0o, East = 90o
Conclusions:
1. Age: continuous up to 16 Gyr
2. Star clusters do not dissipate because of the local
rotation
Star Clusters
in NGC 4038/9
Antennae Galaxy
D = 20 Mpc
Bastian et al., 2009,
ApJ, 701, 607
Positions
of the
slit
8m
telescope
GEMINI
integration
time 4h for
each
spectrum
very young
because
emission is
visible
 WR, O or
B-type stars
still present
In addition: integrated colors from HST photometry
Determination of the extinction, metallicity and age possible
czhel = RV … radial velocity
Bastian et al., 2009, ApJ, 701, 607
With “deltcz” you can measure the kinematics of the host galaxy