A New Zeal for Globular

Clusters

Duncan Forbes, Swinburne

Jean Brodie, UC Santa Cruz

Globular Clusters andGalaxy Formation

Duncan Forbes

Swinburne University

The Fellowship

• Robert Proctor

• Jay Strader

• Soeren Larsen

• Lee Spitler

• Mike Beasley

• Trevor Mendel

(next talk)

Collaborators

Half of this conference,

plus back home at Swinburne…

• Robert Proctor

• Trevor Mendel

• Michael Pierce

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

Bimodal or not Bimodal?

Bimodal Unimodal

Unimodal

Yoon etal. 2006

NGC 5128 Bimodal !

Spitler et al. 2007

Strader et al. 2007

NGC 4472 Bimodal !

The return of the King

(Profile)

Barmby et al. 2007

HST/ACS imaging of GCs in M31

Globular

Cluster

Formation

When ? How ?

Ongoing accretion

Recent mergers

Early formation

Forbes etal 2003

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

Canis Major

4-6 GCs

+ 2 old open clusters

(not BH176, Pal1)

Different age-metallicity relation forthe in situ GCs ?

Forbes et al. 2004

Huxor et al. 2005

Peng NZ conf.

UCDs

Willman1

dwarfs

FFs

M31

Half-light radius vs Magnitude

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

Alpha

elements

Pritzl etal 2005

SN II vs SNIachemicalenrichmenthistory fromhigh resolutionspectra

Metal-poor halo stars

Arnone etal 2005

Hierarchical Merging vs

Early Collapse

“This [early collapse] view has been

tenaciously resistant to challenges.”

De Lucia, Springel, White et al. (2005)

Galaxy

Formation

Merging of darkmatter halos iswell understoodbut details ofbaryon physicsless understood

Dissipative Collapse

Forbes etal 2005

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

Blue GCs vs galaxy mass

Spitler NZ conf

Blue GCs vs environment

Virgo

NGC 4365

AMR

"

Brodie etal 2005

Redshift 0 1 2 5

Galaxy age

NGC 4365 spectrum

"

Leo Group NGC 3379 AMR

"

Pierce, Beasley, Forbes etal 2005

NGC 821

NGC 4649 colours

Forbes etal 2005

Canis Major

Half-light radiusof Canis Major GCsare smaller thantypical Milky WayGCs

Forbes et al. 2004

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

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

dIrr ->

dE ->

dSph ?CM

NGC 4649 AMR

"

Pierce, Bridges, Forbesetal 2006

NGC 1052 vs NGC 1316

Both are recentwet mergers:

Gas and dust

Fine structure

2-3 Gyr old stars

Forbes etal 2001! = N1052, " = N1316

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

Young Elliptical NGC 1052 AMR

"

Pierce, Brodie,Forbes etal 2005

Wet…or Damp Mergers ?

V-I

g-z

Forbes etal 2007

Red

Red

Early-type Galaxies

ACS/Virgo Galaxies

Dry Merger

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)

Virgo galaxies

For low massgalaxies

M/L ~ M -0.67

For high massgalaxies

M/L ~ M +0.5

Forbes 2005

Bekki NZ conf

Virgo galaxies

Bekki, Yahagi & Forbes 2006

SN in 1996

Durrell etal 1996

Tag Team Handover

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

Need blue GCtruncation atz ~5 to givebimodalcolours.

Reionization?

Hierarchical

GC

Formation

Beasley, Baugh, Forbes etal 2002

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

Early GCFormation

Forbes, Brodie &Grillmair (1997)

+ Beasley et al (2002)

Need blue GCtruncation at z >5to give bimodalcolors.

Reionization?

#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

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

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

Blue GCs vs galaxy mass

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

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

LMC/SMC

Cloud collision rate inLMC, and hence GCformation, is dramaticallyenhanced 3.6 Gyrs agowhen LMC/SMC reachclose pericentre.

Bekki et al. 2004