Geneviève Parmentier

(1)

Star Clusters as

Crucial Tracers of Galaxy Evolution

and Probes into Star Formation

Splinter Meeting@AG2010, Bonn, 15 September 2010

Geneviève

Geneviève Parmentier

Parmentier

Argelander

-

Institut f

ür

ü

r

Astronomie

Rheinische

Friedrich

-

Wilhelms

Universit

ä

t Bonn

(2)

2

!

"

#$%$

&

'

Star Clusters: Fast Facts

(3)

3

Cluster mass vs cluster age for a sample of

≅

1,000 clusters

in the Large Magellanic Cloud

A Vital Diagnostic Tool: the Age-Mass Diagram

(4)

4

(

)

*

"

)*&

( +

)

"

+

)&

1

2

log

−

∝

≡

∝

m

d

dN

m

dm

dN

log(dN/dlogm)

log(m)

t=20Myr

t=

2Gyr

(100

××××

more SCs if

CFR=cst)

Age-Mass Diagram and Size-of-Sample Effect

(5)

5

Age-Mass Diagram - Do Not Trust Your Eyes: 1/2

Geneviève Parmentier - Bonn Argelander-Institut für Astronomie

5

/

Size-of-Sample Effect

Cluster mass vs cluster age for a sample of

≅

1,000 clusters

(6)

6

log (m [m

₀

])

log (m [m

₀

])

d

N

/d

lo

g

m

Large Magellanic Cloud

cluster sample:

(7)

7

log (m [m

₀

])

log (m [m

₀

])

d

N

/d

lo

g

m

Large Magellanic Cloud

cluster sample:

Fading limit

Gyr

t

₄dis

=

1

Completeness

limit: M

v

=-4.7

(8)

8

/

Evolutionary fading:

for a given mass,

older clusters are fainter

Size-of-Sample Effect

≅

1,000 clusters

(9)

9

/

Higher SFR

Improved

detection

limit

≅

1,000 clusters

(10)

10

Complete sample

At a given age:

the lower the mass,

the more incomplete

the sample

100%

completeness

limit: Mv=-4.7

≅

1,000 clusters

(11)

11

!

"

#$%$

&

'

Star Clusters: Fast Facts

(12)

12

log (m [M

₀

])

log (m [M

₀

])

d

N

/d

lo

g

m

Modelling of Secular Evolution: Fig.17 in Parmentier & de Grijs (2008),

based on the models of Baumgardt & Makino (2003) and Lamers et al (2005)

75Myr

300Myr

1Gyr

5Gyr

Secular Evol.: Carving a Turnover in the ICMF

12

/

Quicker

Slower

(13)

13

log (m [m

₀

])

log (m [m

₀

])

d

N

/d

lo

g

m

Gyr

t

₄dis

=

1

Completeness

limit: Mv=-4.7

(14)

14

lo

g

(

d

N

/d

t

[M

y

r

-1

])

log ( age [yr] )

Bound Cluster Formation History and

Cluster Dissolution Time-Scale in the LMC

14

/

t

4

dis

= 1Gyr

t

4

dis

= 8Gyr

Secular evolution modelling

Bound Cluster Formation History from the observed cluster age distribution

Parmentier & de Grijs 2008

Predicted

Bound CFR

Observed

age distribution

50Myr – 1.5Gyr

Mass ratio : 0.50

Number ratio: 0.03

(15)

15

, !

-"

. #/ 0

&

1 !

-"

. !2%

+ )&

. !$

low- and high-mass clusters equally

contribute to the total mass (star clusters)

3 4 5 6 logm

m

2

×

dN/dm

α

−

∝

m

dm

dN

:

Function

Mass

Law

-Power

15

/

Cluster Mass Functions: mass versus number

2 3 4 5 6 log(m)

Numbers: 90% 9% 0.9% 0.09%

(16)

16

lo

g

(

d

N

/d

t

[M

y

r

-1

])

log ( age [yr] )

Gas-Embedded Cluster Formation History:

the next step ...

16

/

Violent

relaxation

Secular

evolution

modelling:

(Bound) CFR

Violent

relaxation

modelling:

(Gas-embedded)

CFR

SFR

(17)

17

Violent Relaxation (VR): Observable Signatures

And Prime Parameters

17

/

Intra-Cluster Gas-Expulsion and Violent Relaxation

Observable Imprints upon Star Cluster Systems :

Cluster

mass

distribution,

Cluster

age

distribution,

Cluster

radius distribution

,

Ratio of the total mass in clusters to

the total stellar mass in gas-embedded clusters

Geyer & Burkert (2001)

time

Effects of Gas expulsion - VIOLENT RELAXATION

Cluster expansion

Cluster infant weight-loss and infant mortality

Prime parameters:

(e.g. Baumgardt & Kroupa 2007)

-

SFE

in cluster-forming molecular cores

- Gas expulsion time-scale:

ττττ

GExp

/

ττττ

cross

-

Impact

of external

tidal field

(environment)

(18)

18

log m

[M

[

o

]

L

o

g

[d

N

/d

lo

g

m

]

CMF

3Myr

(

= -2.0

)

CMF

50Myr

(

= -2.0

)

Violent Relaxation: Cluster Mass Functions

18

/

Infa

nt

mo

rta

lity

/

we

igh

t-lo

ss

1

2

log

−

∝

≡

∝

m

d

dN

m

dm

dN

)

(

)

(

end

of

VR

at

Gas

Exp

m

cluster

=

F

bound

×

m

cluster

Time-Evolution of Cluster Mass Functions:

What observers tell modellers …

(19)

19

SFE and Cluster Mass Functions

.

core

bound

cluster

F

SFE

m

(

end

of

VR

)

=

(

)

×

Instantaneous

gas removal,

weak tf impact

F

b

o

u

n

d

SFE

19

/

(

SFE

ε

)

bound

(20)

20

GExp

/

cross

and Cluster Mass Functions

20

/

log ( m [M

o

] )

d

N

/d

lo

g

m

Parmentier, Goodwin et al. (2008)

cross

GExp

bound

F

τ

ε

SFE ,

Constant core radius:

More massive cores have

- a deeper potential well

- a slower gas-expulsion t-s

- can survive despite a

low

SFE of, say, 20%

cross

(21)

21

Tidal Field Impact and Cluster Mass Functions

21

/

−

tidal

mass

half

cross

GExp

cross

r

t

SFE

,

τ

ε

τ

Half-mass radius

r

half-mass

r

core

Circular velocity of iso-T potential

V

c

Galactocentric distance

D

gal

Embedded cluster mass

m

ecl

r

tidal

Weak t.f. impact

Strong t.f. impact

core

ecl

gal

c

ecl

tidal

D

m

SFE

m

V

m

G

r

radius

tidal

Limiting

.

with

,

=

2

/

3

/

1

2

:

(22)

22

Half-mass radius—to—tidal radius ratio

22

/

30

.

0

1

pc

=

r

core

δ

core

mass

half

core

r

m

r

∝

−

∝

2

/

1

01

.

0

1

=

o

core

M

m

pc

r

3

/

1

−

∝

δ

core

tidal

mass

half

m

r

3

/

1

3

/

1

core

ecl

tidal

m

r

∝

3

/

1

04

.

0

1

=

o

core

M

m

pc

r

4100

(23)

23

F

bound

and Tidal Field Impact

23

/

30

.

0

1

pc

=

r

core

2

/

1

01

.

0

1

=

o

core

M

m

pc

r

3

/

1

04

.

0

1

=

o

core

M

m

pc

r

4100

(24)

24

The m

core

- r

core

Diagram as a Diagnostic Tool

24

/

30

.

0

1

pc

=

r

core

2

/

1

01

.

0

1

=

o

core

M

m

pc

r

3

/

1

04

.

0

1

=

o

core

M

m

pc

r

External tidal field strength:

(V

c

, D

gal

)

rh/rt in [log(r),log(m)]

rh/rt < 0.05: tf does not matter

(does not necessarily imply weak tf !)

rh/rt > 0.15: cluster survivability

demands long

ττττ

GExp

/

ττττ

cross

and

high SFE

tf impact

impedes cl.

survivability

As if no external tf

core

r

core

(25)

25

/

Cluster infant weight-loss

is mass-independent, the shape of

the cluster mass function does not evolve during VR

3

/

1

04

.

0

1

=

o

core

M

m

pc

r

log(m)

log (dN/dlogm)

CMF

Ecl.MF

F

bound

Constant Volume Density Cores:

mass-independent

infant weight-loss

core

4100

Tidal Field Impact and Cluster Mass Functions:

Probing the cluster-forming core mass-radius relation

(26)

26

Tidal Field Impact and Cluster Mass Functions

26

/

log ( m [M

o

] )

d

N

/d

lo

g

m

SFE=0.40 D_gal=5kpc

2

/

1

01

.

0

1

:

=

Σ

o

core

M

m

pc

r

F

bound

Constant Surface Density Cores:

When more

massive

(27)

27

lo

g

(

d

N

/d

t

[M

y

r

-1

])

log ( age [yr] )

Galaxy Star Formation Histories: even

a long journey starts with one single footstep ...

27

/

Secular

evolution

modelling:

(Bound) CFR

Violent

relaxation

modelling:

(Gas-embedded)

CFR

SFR

−

tidal

mass

half

cross

GExp

bound

r

F

SFE

,

τ

ε

(28)

28

Core mass-radius relations: observations

28

/

Density profiles:

(r

core

,m

core

) @ 1E4 cm

-3

Mueller+02

?

Core mass-radius diagram:

imprint of

-

measurement method

,

or of

-

cluster-formation physics

?

Limited baseline in

cluster-forming core mass

Lack of high-mass data

core

or

core

?

when picking-up obs data

read (part of) the paper

(29)

29

Core mass-radius relations: so what ... ?

29

/

- Red circles:

C

18

O cores

showing signs of

SF activity

C

18

O

Car GMC (Yonekura+05)

Orion B (Aoyama+01)

(30)

30

Core mass-radius relations: so what ... ?

30

/

- Red circles:

C

18

O cores

showing signs of

SF activity

C

18

O

-

Most of them also host a

clump at

1E5 cm

-3

(H

13

CO

+

)

SF takes place in regions

where the density is higher

than a threshold, i.e. only in the

densest regions of C

18

O cores

Orion B (Aoyama+01)

(31)

31

* *

Core mass-radius relations: so what ... ?

31

/

- Red circles:

C

18

O cores

showing signs of

SF activity

-

Most of them also host a

clump at

1E5 cm

-3

(H

13

CO

+

)

SF takes place in regions

where the density is higher

than a threshold, i.e. only in the

densest regions of C

18

O cores

C

18

O

Why ? Efficient decay of turbulence …

(Klessen 2003)

Consequence: the local SFE must be measured over

the cluster volume, not over the whole C

18

O core

H

13

CO

+

observations suggest:

Constant volume density cluster-forming cores,

which lead to mass-independent infant weight-loss (t.f. impact),

as suggested by observations

Orion B (Aoyama+01)

(32)

32

Conclusions

32

/

lo

g

(

d

N

/d

t

[M

y

r

-1

])

log ( age [yr] )

Observed age

distribution of

LMC star clusters

SFH

Properties of young star cluster systems

sharp insights into the clustered

mode of star formation

star formation conditions determine

what mass fraction clusters lose as they age

information needed to reconstruct galaxy SFH

time-variations ? (e.g. metallicity)

Most exciting years are

still to come:

HERSCHEL, ALMA, …

“Even a long journey starts

with a one sinle step”