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The Globular Cluster Systems of Ellipticals and Spirals

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

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  1. The Globular Cluster Systems of Ellipticals and Spirals Duncan A. Forbes Centre for Astrophysics & Supercomputing, Swinburne University

  2. Collaborators Jean Brodie (Lick Observatory) Carl Grillmair (JPL/SIRTF) John Huchra (Harvard-Smithsonian) Markus Kissler-Patig (ESO) Soeren Larsen (Lick Observatory)

  3. 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

  4. 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

  5. Metallicities Number of metal-rich GCs scale with the bulge Forbes, Larsen & Brodie 2001

  6. Spiral vs Elliptical GC Systems • Numbers, SN • Luminosities • Metallicities • Abundances • Sizes • Ages • Kinematics • Spatial Distribution

  7.  = 0.2% Number per unit Starlight McLaughlin (1999) proposed a universal GC formation efficiency  = MGC / Mgas + Mstars = 0.26 % Mgas = current Xray gas mass

  8.  = 0.1% Blue Globular Clusters per unit Starlight Halo GCs in the MW, M31 and M104 follow the general trend.

  9.  = 0.1% Red Globular Clusters per unit Starlight Bulge GCs in the MW, M31 and M104 follow the general trend.

  10. 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

  11. 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

  12. Metallicities Previously …... Harris 2000

  13. 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 )

  14. 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).

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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.

  22. 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

  23. 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

  24. Spiral vs Elliptical GC Systems • Numbers, SN • Luminosities • Metallicities • Abundances • Sizes • Ages • Kinematics • Spatial Distribution

  25. 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

  26. 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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