a new zeal for globular clusters · milky way gcs datasets: cohen etal. 1998, puzia etal. 2002,...
TRANSCRIPT
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A New Zeal for Globular
Clusters
Duncan Forbes, Swinburne
Jean Brodie, UC Santa Cruz
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Globular Clusters andGalaxy Formation
Duncan Forbes
Swinburne University
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The Fellowship
• Robert Proctor
• Jay Strader
• Soeren Larsen
• Lee Spitler
• Mike Beasley
• Trevor Mendel
(next talk)
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Collaborators
Half of this conference,
plus back home at Swinburne…
• Robert Proctor
• Trevor Mendel
• Michael Pierce
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Two Towers
Most (perhaps all) large galaxies reveal two
distinct sub-populations of globular clusters.
V-I = 0.95 1.15 [Fe/H] = -1.5 -0.5
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Bimodal or not Bimodal?
Bimodal Unimodal
Unimodal
Yoon etal. 2006
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NGC 5128 Bimodal !
Spitler et al. 2007
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Strader et al. 2007
NGC 4472 Bimodal !
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The return of the King
(Profile)
Barmby et al. 2007
HST/ACS imaging of GCs in M31
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Globular
Cluster
Formation
When ? How ?
Ongoing accretion
Recent mergers
Early formation
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Forbes etal 2003
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Ongoing GCAccretion
Sgr Dwarf Galaxy
M54 (dwarf nucleus)
+ 5 GCs + Whiting 1
Well fit by a closedbox model
Pal12, Ter7 [!/Fe] ~ 0
M54 [!/Fe] ~ +0.3(Pritzl et al. 2005)
Forbes et al. 2004 Fellhauer NZ conf.
Whiting-1
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Canis Major
4-6 GCs
+ 2 old open clusters
(not BH176, Pal1)
Different age-metallicity relation forthe in situ GCs ?
Forbes et al. 2004
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Huxor et al. 2005
Peng NZ conf.
UCDs
Willman1
dwarfs
FFs
M31
Half-light radius vs Magnitude
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Milky Way GCs
Datasets: Cohen etal. 1998, Puzia etal. 2002,
Schiavon etal. 2005
!~50 MW GCs with S/N ~ 100
Test SSP models using a multi-line fitting
technique to Lick indices
Compare results to `known’ values
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Alpha
elements
Pritzl etal 2005
SN II vs SNIachemicalenrichmenthistory fromhigh resolutionspectra
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Metal-poor halo stars
Arnone etal 2005
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Hierarchical Merging vs
Early Collapse
“This [early collapse] view has been
tenaciously resistant to challenges.”
De Lucia, Springel, White et al. (2005)
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Galaxy
Formation
Merging of darkmatter halos iswell understoodbut details ofbaryon physicsless understood
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Dissipative Collapse
Forbes etal 2005
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Recent Mergers
To form an Ellipticalgalaxy GC system, newmetal-rich GCs (redafter ~2Gyrs) arerequired to form. Thenumber of metal-poor(blue) GCs is unchanged.
Ashman & Zepf 1992
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Blue GCs vs galaxy mass
Spitler NZ conf
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Blue GCs vs environment
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Virgo
NGC 4365
AMR
"
Brodie etal 2005
Redshift 0 1 2 5
Galaxy age
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NGC 4365 spectrum
"
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Leo Group NGC 3379 AMR
"
Pierce, Beasley, Forbes etal 2005
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NGC 821
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NGC 4649 colours
Forbes etal 2005
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Canis Major
Half-light radiusof Canis Major GCsare smaller thantypical Milky WayGCs
Forbes et al. 2004
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Spiral+dwarf with Keck
• March 2003
• 1 hr long-slit spectrum
• Spiral velocity = 43,433 +/- 99 km/s
• Dwarf velocity = 43,445 +/- 225 km/s
• Redshift = 0.15
• Distance = 2 billion light years
• Spiral galaxy mass = 1012 solar masses
• Dwarf galaxy mass = 1010 solar masses
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Dwarf properties
Reff = 1 kpc
!eff = 23 V mag/sq arcsec
!o = 21 V mag/sq arcsec
Mv = -16.0
Recent starburst
Twisted isophotes
=> dwarf ellipticalwith ~10 GCs
Forbes etal 2003
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dIrr ->
dE ->
dSph ?CM
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NGC 4649 AMR
"
Pierce, Bridges, Forbesetal 2006
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NGC 1052 vs NGC 1316
Both are recentwet mergers:
Gas and dust
Fine structure
2-3 Gyr old stars
Forbes etal 2001! = N1052, " = N1316
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Multi- GC systems
"
Strader et al. 2005
Both red andblue sub-pops arecoeval at~12 Gyr old.
Most GCformation inmassiveellipticalshappened atz > 2, not inrecentmergers. Blue Red
Old age isochrones
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Young Elliptical NGC 1052 AMR
"
Pierce, Brodie,Forbes etal 2005
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Wet…or Damp Mergers ?
V-I
g-z
Forbes etal 2007
Red
Red
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Early-type Galaxies
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ACS/Virgo Galaxies
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Dry Merger
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Galaxy Bimodality
MV ~ -19.5, M#~3x1010 Mo, Mhalo~6x1011Mo
Luminosity function, Colour-magnitude,Star formation rates, bulge/disk ratio,X-ray emission, stellar age, AGNemission, M/L ratio
Globular Cluster Specific Frequency
Transition from hot accretion flows to coldaccretion and SN winds (Dekel)
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Virgo galaxies
For low massgalaxies
M/L ~ M -0.67
For high massgalaxies
M/L ~ M +0.5
Forbes 2005
Bekki NZ conf
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Virgo galaxies
Bekki, Yahagi & Forbes 2006
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SN in 1996
Durrell etal 1996
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Tag Team Handover
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GC-galaxy properties
Brodie & Strader 2006
Similar slope tostar-galaxyrelation.
Providesconstraints onhierarchicalmerging.
MP GCs formingat very high z“knew” the galaxyto which theywould ultimatelybelong
See also Peng et al 2006
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Need blue GCtruncation atz ~5 to givebimodalcolours.
Reionization?
Hierarchical
GC
Formation
Beasley, Baugh, Forbes etal 2002
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Blue TiltA mass-metallicityrelation for blueGCs.
Due to self-enrichment in darkmatter mini-halos?
BCGs: Harris et al2006
Summed dEs:Mieske et al 2006
Sombrero: Spilteret al 2006
Spirals: Forde etal 2007 Strader et al. 2006 Jordan NZ conf
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Early GCFormation
Forbes, Brodie &Grillmair (1997)
+ Beasley et al (2002)
Need blue GCtruncation at z >5to give bimodalcolors.
Reionization?
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#CDM…
N-body simulationssuggest dark matterhalos “sitting” on top oflarge overdensitiescollapse first (z>10)
The majority of thesehalos combine to formmassive galaxies at z=0
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The Biasing
Scenario
• “Biasing” - halos on top oflarge over densities collapsebefore those on periphery
• Reionization truncates
metal-poor GC formation
• Halos that collapse first producemetal-poor GCs of higher metallicity
• First-collapsing halos produce the metal-poor subpopulationof the most luminous galaxies
• More distant halos survive independently to become dwarfgalaxies
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Biased Hierarchical MergingMust simultaneously accommodate:
1) MP GC metallicity – galaxy Lrelation
2) Some merging since z~2MP GC relation was different at
high z• Merging was biased – direct
result of, and strong endconstraint on, hierarchicalstructure formation
• MP relation rules out mergersand accretion but only in thelocal universe for structureforming at present day
Brodie & Strader2006
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Blue GCs vs galaxy mass
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Reionization• If blue GC formation is truncated by reionization GC
surface density distributions probe epoch &(in)homgeneity of reionization
• Blue GC surface density distributions for galaxies ofdifferent masses and environments
Moore et al (2005), Diemand et al (2005) Bassino et al (2006)
MilkyWay Fornax
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Conclusions• Although ongoing accretions and recentmergers contribute, most GC formation isearly (z > 2, age > 10 Gyrs), i.e. massive galaxiesformed early
• GC SN bimodality mirrors galaxy bimodality
• GCs provide the best observable link betweenbaryons and dark matter
• GC scaling relations constrain hierarchicalgrowth: red GCs trace bulge formation, bluestrace DM halos at earliest times + reionization
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LMC/SMC
Cloud collision rate inLMC, and hence GCformation, is dramaticallyenhanced 3.6 Gyrs agowhen LMC/SMC reachclose pericentre.
Bekki et al. 2004