The globular cluster systems of ellipticals and spirals
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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)

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The globular cluster systems of ellipticals and spirals l.jpg

The Globular Cluster Systems of Ellipticals and Spirals

Duncan A. Forbes

Centre for Astrophysics & Supercomputing, Swinburne University


Collaborators l.jpg
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 l.jpg
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 l.jpg
Milky Way Globular Cluster System

4 sub-populations:

Metal-rich (~50)

Bulge (RGC < 5 kpc)

Thick disk (RGC > 5 kpc)

Metal-poor (~100)

Old Halo (prograde)

Young Halo (retrograde)

Young halo + 4 Sgr dwarf GCs = Sandage noise


Metallicities l.jpg
Metallicities

Number of metal-rich GCs scale with the bulge

Forbes, Larsen & Brodie 2001


Spiral vs elliptical gc systems l.jpg
Spiral vs Elliptical GC Systems

  • Numbers, SN

  • Luminosities

  • Metallicities

  • Abundances

  • Sizes

  • Ages

  • Kinematics

  • Spatial Distribution


Number per unit starlight l.jpg

= 0.2%

Number per unit Starlight

McLaughlin (1999) proposed a universal GC formation efficiency

 = MGC / Mgas + Mstars

= 0.26 %

Mgas = current Xray gas mass


Blue globular clusters per unit starlight l.jpg

= 0.1%

Blue Globular Clusters per unit Starlight

Halo GCs in the MW, M31 and M104 follow the general trend.


Red globular clusters per unit starlight l.jpg

= 0.1%

Red Globular Clusters per unit Starlight

Bulge GCs in the MW, M31 and M104 follow the general trend.


The elliptical galaxy formally known as the local group l.jpg
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 l.jpg
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


Metallicities12 l.jpg
Metallicities

Previously …...

Harris 2000


Metallicities13 l.jpg
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 )


Slide14 l.jpg

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).


Slide15 l.jpg

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


Slide16 l.jpg

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


Slide17 l.jpg

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 l.jpg

Galaxies

Abundances

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 l.jpg
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


Slide20 l.jpg
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

15 Gyrs

0.92

–1.5

13 Gyrs

1.12

–0.5

Age = 2 Gyrs, ie similar to the MW old halo and bulge GCs


Kinematics l.jpg
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 l.jpg
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 distribution23 l.jpg
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 X-ray gas profile ?)

BlueRedRed

Ellipticals Halo `Bulge’ Disk ?

Spirals Halo Bulge Disk


Spiral vs elliptical gc systems24 l.jpg
Spiral vs Elliptical GC Systems

  • Numbers, SN

  • Luminosities

  • Metallicities

  • Abundances

  • Sizes

  • Ages

  • Kinematics

  • Spatial Distribution


Formation timeline l.jpg
Formation Timeline

Blue GCs form in metal-poor gas with little or no knowledge of potential well. Halo formation. Common to all galaxies.

15 Gyrs

Clumpy collapse of largely gaseous components form metal-rich red GCs and `bulge’ stars. Synchronous star formation event.

13 Gyrs

Field mergers of Sp + Sp  E, with SN ~ 3.

Now

Time


Conclusion l.jpg
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)


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