Download No Slide Title

The Globular Cluster Systems
of Ellipticals and Spirals
Duncan A. Forbes
Centre for Astrophysics &
Supercomputing, Swinburne University
Collaborators
Jean Brodie (Lick Observatory)
Carl Grillmair (JPL/SIRTF)
John Huchra (Harvard-Smithsonian)
Markus Kissler-Patig (ESO)
Soeren Larsen (Lick Observatory)
Milky Way Bulge Clusters
The inner metal-rich GCs are:
• spherically distributed
• similar metallicity to bulge stars
• similar velocity dispersion to bulge stars
• follow the bulge rotation
 Bulge GCs (Minniti 1995).
A similar situation exists for M31
Milky Way Globular Cluster System
4 sub-populations:
Metal-rich (~50)
Metal-poor (~100)
Bulge
(RGC < 5 kpc)
Old Halo
(prograde)
Thick disk
(RGC > 5 kpc)
Young Halo
(retrograde)
Young halo + 4 Sgr dwarf GCs = Sandage noise
Metallicities
Number of metal-rich GCs scale with the bulge
Forbes, Larsen & Brodie 2001
Spiral vs Elliptical GC Systems
Numbers, SN
 Luminosities
 Metallicities
 Abundances
 Sizes
 Ages
 Kinematics
 Spatial Distribution

Number per unit
Starlight
McLaughlin (1999)
proposed a universal
GC formation
efficiency
 = MGC / Mgas + Mstars
= 0.26 %
Mgas = current
Xray gas mass
 = 0.2%
Blue Globular Clusters
per unit Starlight
Halo GCs in the MW,
M31 and M104 follow
the general trend.
 = 0.1%
Red Globular
Clusters per unit
Starlight
Bulge GCs in the
MW, M31 and
M104 follow the
general trend.
 = 0.1%
The Elliptical Galaxy
Formally Known as
The Local Group
Merging the Local
Group globular
clusters
N = 700 +/- 125
MV (aged) = – 20.9
SN = 3.0 +/- 0.5
Universal luminosity
function
Luminosities
A Universal Globular Cluster Luminosity Function
MV

Ellipticals
–7.33 +/- 0.04
1.36 +/- 0.03
Spirals
–7.46 +/- 0.08
1.21 +/- 0.05
Even better agreement if only blue GCLF used ?
Ho = 74 +/- 7 km/s/Mpc
GCLF
Ho = 72 +/- 8 km/s/Mpc
HST Key Project
Harris 2000
Metallicities
Previously …...
Harris 2000
Metallicities
Recent developments
 Use of Schlegel etal 1998 rather than
Burstein & Heiles 1984.
( typically bluer by  AV = 0.1 )
 Use of Kissler-Patig etal 1998 for V-I 
[Fe/H] based on Keck spectra of NGC
1399.
( red GCs more metal-poor by 0.5 dex )
Metallicities
All large galaxies (with
bulges) reveal a
similar bimodal
metallicity distribution.
All galaxies
( MV < –15 ), reveal a
population of GCs
with [Fe/H] ~ –1.5.
The WLM galaxy has
one GC, [Fe/H] = –1.52
age = 14.8 Gyrs
(Hodge et al. 1999).
Metallicity vs
Galaxy Mass
Blue GCs <2.5
V–I ~ mass ?
V–I = 0.93
Pregalactic ?
Red GCs ~4
V–I ~ mass
Forbes, Larsen & Brodie 2001
Metallicity vs
Galaxy Mass
Red GC relation
has similar slope to
galaxy colour
relation.
Red GCs and
galaxy stars
formed in the
same star
formation event.
Forbes, Larsen & Brodie 2001
Colour - Colour
Galaxy and GC
colours from the
same observation.
In some galaxies
the red GCs and
field stars have the
same metallicity
and age  gaseous
formation.
Also NGC 5128
(Harris et al. 1999)
Forbes & Forte 2001
Abundances
Galaxies
High Resolution
[Mg/Fe] = +0.3
Milky Way
Low Resolution
[Mg/Fe] = 0.0
MW, M31, M81
NGC 1399, NGC 4472
SNII vs SNIa, IMF,
SFR ?
Terlevich & Forbes 2001
Sizes
For Sp  S0 E  cD
the GCs reveal a size–
colour trend. The blue GCs
are larger by ~20%.
This trend exists for a
range of galaxies and
galactocentric radii.
Larsen et al. 2001
Ages
Assume: blue GCs in ellipticals are old (15 Gyrs) and
metal-poor ([Fe/H = –1.5) and V–I = 0.2
[Fe/H]
Age
V–I
–1.5
15 Gyrs
0.92
–0.5
13 Gyrs
1.12
Age = 2 Gyrs, ie similar to the MW old halo and
bulge GCs
Kinematics
In the Milky Way V/ for the bulge GCs
(0.87) is greater than for the halo (0.24).
In M49 the metal-rich GCs have V/
less than V/ for the metal-poor GCs
(Bridges 2001). Need to study more
giant ellipticals.
Spatial Distribution
The surface density
profiles of GC systems
reveal an inner constant
density `core’ with a
power-law decline in the
outer parts.
The size of inner core of
the GC system varies
with host galaxy
luminosity.
Forbes et al. 1996
Spatial Distribution
In Ellipticals:
Red GCs are centrally concentrated, often
have similar azimuthal and density profiles (and
colour) to the `bulge’ light.
Blue GCs are more extended. Associated with the
halo ? (Does the blue GC density profile follow the Xray gas profile ?)
Blue
Red
Red
Ellipticals
Halo
`Bulge’
Disk ?
Spirals
Halo
Bulge
Disk
Spiral vs Elliptical GC Systems
 Numbers,
SN
 Luminosities
 Metallicities
 Abundances
 Sizes
 Ages
 Kinematics
 Spatial Distribution
Formation Timeline
15
Gyrs
Blue GCs form in metal-poor gas with little or no
knowledge of potential well. Halo formation.
Common to all galaxies.
13
Gyrs
Clumpy collapse of largely gaseous
components form metal-rich red GCs and
`bulge’ stars. Synchronous star formation event.
Now
Field mergers of Sp + Sp  E, with SN ~ 3.
Time
Conclusion
The blue (metal-poor) and red (metal-rich)
GCs seen in Ellipticals, Spirals and Dwarf
Galaxies are essentially the same thing.
Seyfert 1 vs Seyfert 2 (orientation)
QSO vs Quasar (optical/radio)
Sun vs stars (distance)