Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/LVmeeting/magsys_pres/LMC07a.pdf Дата изменения: Sun Aug 5 03:27:43 2007 Дата индексирования: Tue Oct 2 16:39:00 2012 Кодировка:

Origin of the old globular cluster system in the LMC

=
NGC 1850

Z=10 GC/halo formation Z=2 disk formation Z=0.4 interaction with SMC ..............

(GC) (The LMC) (The Rosetta Stone)

Kenji Bekki (UNSW, Australia)


GCs and Globular cluster systems (GCSs)

<

GC:47 Tuc

GCS properties: Space distributions , Kinematics, Metallicity.....


Globular cluster systems (GCSs) in different Hubble types.

Spiral: M31

Irregular: LMC GC-less galaxies.

Elliptical:M87

Leo A

M32


Why merging/accretion in the Galaxy formation (Searle & Zinn 1978; SZ)?: GCs as fossil records of the Galaxy formation.
· No significant metallicity gradient in the Galactic GC. · A possible broad range of age in the outer halo GCs etc... (SZ 1978).

[Fe/H]

Radius (kpc)



A big question:

What do physical properties of the GCS of the LMC tell us about the LMC formation ?


A specific question:

Origin of the observed kinematical differences between the stellar halo and the old GCS in the LMC.


Rotational kinematics in the old GCS of the LMC (Freeman et al. 1983)?

V

rot

~ 41 km/s, ~ 17 km/s, V/~2.4


Rotational kinematics in the LMC'S GCS.

(Freeman et al. 1983)

(Grocholski et al. 2006)


The old stellar halo properties in the LMC.
· Vrot<10 km/s for the stellar halo (for RR Lyrae stars), ~53 km/s, and V/<0.2 (e.g., Minniti et al. 2003). · An exponential (projected) radial density profile (e.g., Alves 2004). · A flattened inner stellar halo (Subramaniam 2006) ?


The non-rotating stellar halo vs the rotating old GCS in the LMC ?
LMC

GCS: V/~2.4 Halo: V/~0.2
GC Halo field stars

LMC


The non-rotating stellar halo vs the rotating old GCS in the LMC
LMC

GCS: V/~2.4 Halo: V/~0.2
The Galaxy

GCS: V/~0.3 Halo: V/~0.3
(e.g., for r/v; Freeman 1993)


Question:

Are these kinematical properties consistent with the LMC formation model (based on the CDM) ?
(1) Bekki (2007): galaxy-scale simulations (2) Bekki & Yahagi (2007): Large-scale ones.



The formation of the LMC's GCS.
(1) GCSs from 100 Mpc-scale simulations (e.g., Yahagi & Bekki 2005) (2) GCSs from galaxy-scale simulations (Bekki 2007).


GC/field star formation in low-mass galaxies embedded by dark matter halos at high redshifts (z>6) Protogalaxy
Z>6

200 kpc

Field stars GC

All halos with masses larger than ~ 107 Msun have GCs.

Dark matter halo


Can we find a model with the GCS having V/ ~ 2 ?
i ztrun

(V/)FS ?

(V/)GC ?


Stellar halo Results: Spatial distributions of the stellar halo and the GCS in the LMC GCs


Kinematics

Vrot (km/s) (km/s)
Halo: V/~0.57 GC: V/~0.60

R


Kinematics

Vrot (km/s) (km/s)
Halo: V/~0.21 GC: V/~0.31

R


Stellar halo

Spatial distributions of the low- (initial low density) model.
GCs

More flattened...


Kinematics

Vrot (km/s) (km/s)
Mean of three projections

Halo: V/~0.60 GC: V/~0.56

R


Inconsistency between simulations and observations.

(V/)

GC

Obs: V/~2.4 Sim: V/~0.3


Discussions: Lessons from unsuccessful models.
· No/little GC formation in low-mass halos at high-z (>6) : the presence of the threshold halo mass for GC formation ? · ``Dissipative'' GC formation at the very early epoch of the LMC's disk formation : The LMC's GC are slightly younger than the Galactic counterparts ?


Discussions: Two related problems.
· Why do less luminous galaxies have GCSs with rotation (e.g., Olsen et al. 2004 for galaxies in the Sculptor group) ? · Why do the GCS/stellar halo in the Galaxy appear to show no/little kinematical differences ?


Conclusions: Still mysterious GCS kinematics in the LMC
· Failures of the present LMC formation models in reproducing the rotational kinematics of the LMC's GCS. · A possible threshold halo mass for GC formation and GC formation at the very early epoch of the LMC's disk formation ??