Formation and Dynamical
Evolution of Globular Cluster
Kenji Hasegawa(Univ. Tsukuba, Doctoral Candidate)14Gyr1Gyr
0.1GyrDark Age 1st Part
0.5MyrGlobularCluster
Formation

2nd Part
DynamicalEvolution(～10Gyr)

Present Day
GC

CMB
Pop III
Reionization
Birth of Galaxies
Massive BH
Birth of Stars
Solar System
Planets

1st PART

Formation of Globular Cluster
within UV Radiation Field
Collaborators
Masayuki Umemura (U. Tsukub)
Tetsu Kitayama (U. Toho)

Reionization and GC Formation Epoch
WMAP 3year (Page et al. 2006)
Reionization epoch ~13Gyr ago

V.S

The age distribution of GCs
Mean age of GCs ~12Gyr

It indicates that manyGCs formed after
cosmic reionization !!
Ionizeduniverse

GCs could form within
UV radiation field ?
Puzia et al. (2005)

negative

Importance of UV Radiation
9Photoheating
Gas temperature ~ 104K

9Photodissociation(H2)UV radiation might
suppress theformations of GCs?

Gas clouds can not coolbelow 104K

★OBJECTIVE★
We explore the possibility that GCs
form within UV radiation field !!

Simulation of GC Formation within UV Radiation
1D spherical symmetric Lagrangian scheme(Kitayama et al. 2001)

Gas dynamics

d 2 rb
GM (< rb )2 dP=−−r+ Λ 0 H 02 rb + f radπ4b22dt
dmbrb

P = (γ − 1) ρ bu =kB ρ bT
μmp

Ω0=0.3, Ωb=0.05, Λ0=0.7, h=0.7

DM dynamics

dmb= 4πrb2 ρ bdrb

du P dρ b Γ − Λ= 2+ρbdt ρ b dt

ΛCDM universe：universe

T < 2000 K
Vr < 0dρ>0dt
dT<0dtSF criteriad 2 rdGM (< rd )2Hrd=−+Λ0022dtrd

Star dynamics

d 2 rsGM (< rs )=−2dtrs2

・RT of UV photons ⇒Determine the heating and the chemical reaction rate
・Non-equilibrium of chemistry ⇒Determine the cooling rate (H2)

Calculation Procedure

STARTThe cloud is stillin linear regime.

～100

UV radiation on !!
9Black Body with Teff=105K
910-3 < I21 < 103
I21 is a intensity at Lyman
limit in unit of 10-21 erg cm-2
s-1Hz-1str-1=20

Evolution of the CloudEvolution of the Cloud
Both shells are
ionized when
they areirradiated byUV radiation.

Both shells areheated up to10^4K

Evolution of the Cloud

The shell withspersonic infall
velocity keeps
contracting .

Evolution of the CloudSF criterion

Cools via H2
coolingMass Distribution
Strong UV radiation (I21>1)←ＤＭStarStararearebornbornatatinner
innerregion
regionStarofthe
thecloud.
cloud.The
Theenergy
energyofdissipationisisstrong
strong!!!!
dissipation

Baryondominated

Compact star cluster forms !!
⇨ GC like (with DM halo)
Weak UV radiation (I21<0.1)←ＤＭ

Starsarearebornbornatatearlier
earlierStars
dynamicalstage.
stage.
dynamicalStar
DM dominated and low density starcluster forms ! ⇨ dSphs like2nd PARTDynamical Evolution ofGlobular Cluster
Collaborator
Masayuki Umemura (Tsukuba University)
FIRST Project Team

Setup for the Simulation¾Number of particle：N*=214, NDM = 218 (m*/mDM= 10.39)¾External tidal field*NFW type potential (with Mgal= 109M~, Rvir = 294pc, c = 10)¾Initial condition：Obtained by our simulation of GC formation.
★Two-body relaxation (Spitzer ＆ Hart 1971)
3/2
⎛⎞
⎞
⎛⎛
⎞rM
1Msunt rh ≈ 5.76 ×10 9 ⎜ 6⎟⎜ h ⎟⎟ ⎜⎝ 10 M sun ⎠ ⎝ m ⎠⎝10pc ⎠1/ 2←ＤＭStar
Cosmic age(~14Gyr)corresponds to 2.6 trh.

Evolution of Observable Profile
9The profile changes as the star cluster evolves !!
STARDM

Inner partThe core shrinks
via two-bodyrelaxation.

Outer part
Tidal stripping

NDM=2^18⇨ The cluster
mass decreases !!

Evolution of the Cluster Mass
We assume a mass within 50pc from the center as the cluster mass.
Simulation
Present day

DM is selectively
stripped by tidal force!!

The star clusterwith a small
amount of DM
survive !!
Observation
GCs have low
mass-to-lightratio M/L ~ 2Comparison with observations
GlobularClustersdwarfspheroidals

Comparison with observations
GlobularClusters

dwarfspheroidals

T = 1.338, 1.784, 2.233, 2.676trh are shownSummary★Globular Cluster Formation within UV radiation Field
The cloud is ionized !!
Strong UV radiation
If the cloud has supersonic infall velocity, the cloud keeps contracting.
Star formation is delayed and stars are born at inner region of the cloudCompact star cluster forms
Weak UV radiation

Shielding effect works well !!

Stars are born at earlier dynamical stage. Diffuse star cluster forms★Dynamical Evolution of Globular Cluster
9Observable profiles change as the cluster evolves.
9DM halo is stripped by tidal interaction with the hostgalaxy.
Low mass-to-light ratio.
9Simulation results are well consistent with observations.

Our GC formation scenario is plausible to explain the observed GCs

Result: Strong UV case
2σCDM
Self-Shielding
Effect
1σCDM

Evaporate

SupersonicInfallingResult:Weak UV Case