Myung Gyoon Lee (Dept of Physics and Astronomy, Seoul National University) With Ho Seong Hwang (CfA) and Hong Soo Park (NAOJ) 2013. 10. 22 Dynamics of Disk Galaxies, The 7 th Korean Astrophysics Workshop, Oct 21-24, SNU, Korea
M31 is an ideal galaxy to study the dynamics of disks as well as bulges & halos in spiral galaxies. Globular clusters (GCs) are a powerful tool for understanding the kinematics of a galaxy. Overviewing the kinematics of GCs in M31. What do they tell about formation of M31? Subaru/HSC image(naoj)) 2
Why does M31 have 4x more GCs than MWG? Is there a halo in M31? It has been controversial whether it has a giant bulge or a wimpy halo. Is the M31 halo rotating, while the MW halo rotates little? (Huchra et al 1991, Perrett et al. 2002, Lee et al. 2008, Veljanoski et al. 2013) How did M31 form? The M31 bulge is a classical bulge with pseudobulge trimmings in the outer part. (Mould 2013, Courteau et al, 2011) 3
1. Introduction of the GC system in M31 2. Spatial distribution of GCs 3. Kinematics of disk GCs 4. Kinematics of bulge & halo GCs 5. Formation of M31 6. Summary 4
Our previous kinematic study (Lee+ 2008) N(GCs with radial velocity) = 504 Concluded There is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. However, no age information was used for analysis. Today s M31 GC sample: (Lee+ 2013, complied from previous studies, Kim+2007,Caldwell+2011) N(GCs with v, age) = 612 (the largest sample) Young GCS (156 GCs with t<3 Gyr) Old GCS (456 GCs with t>3 Gyr). Metal-poor GCs (~290 GCs with [Fe/H]<-0.9) Metal-rich GCs (~130 GCs with [Fe/H]>-0.9) 5
Old GCs are redder & brighter than young GCs. Old GCs have a broad range of color, indicating a large [Fe/H] spread as well as varying reddening. Young Old Lee et al (2013) 6
Young GCs are located mainly along the 12kpc ring in the disk. Old GCs are in a wider area, with an elongated central concentration! (10 =2.3kpc) Young Old Lee et al (2013) 7
Old metal-poor GCs: spread over a wide area Old metal-rich GCs: stronger central concentration with a wide tail Metal-poor Lee et al (2013) Metal-rich 8
M31: three components Inner component at <10kpc Middle comp. (10<R<30 kpc) Outer comp. (R>30 kpc) Metal-poor GCs shows a more extended profile than metalrich GCs. Metal-rich GCs shows a bulge component at R<2 kpc. MW GCs: two components Lee et al (2013) Bulge? stellar halo 9
Spatial distribution of young GCs: along the 12kpc ring! Velocity vs. major axis(x) and minor axis(y): Young GCs are rotating fast around the minor axis. receding approaching Lee et al (2013) 10
Young GCs at Y <1kpc. Comparison with other Pop I tracers (HI, CO, HII) & Pop II tracer(pn) Rotation curve: similar to other Pop I tracers Velocity dispersion: much lower than PN Young GCs follow a rotation of a thin disk! Young Disk GC Lee et al (2013) HI PN Young Disk GC 11
Old GCs at Y <1 kpc. Old GCs in the central region (at R<5kpc) show a large velocity dispersion, which shows the existence of a bulge. HI Old disk GCs at 5<R<10kpc rotate a little slower than the thin disk and with much larger velocity dispersion, which shows existence of a thick disk or a metal-rich halo. Bulge? Old Disk GC Thick disk or halo? PN 12
Spatial distribution of old GCs: a wide distribution with concentration along the major axis Velocity vs. major axis(x) and minor axis(y): Old GCs are rotating around the minor axis. receding approaching Lee et al (2013) 13
Metal-poor GCs show a weaker rotation! Metal-rich GCs: Overall stronger rotation High velocity dispersion in the central region (bulge)! Fast rotation in the central region at R<2kpc (bar Morrison+ 2011) Metal-poor GCs Metal-rich GCs Lee et al (2013) 14
A wide range of metallicity! A schematic division: Bulge: high [Fe/H] Thin disk: Thick disk (or red halo?): Halo: low [Fe/H] 15
Low [Fe/H]: circular (halo) Medium [Fe/H]: elongated (halo?) High [Fe/H]: compact (bulge!) 16
A large range of age for M31 GC. Different from MW GCs. Lee et al (2013) 17
Bulge very metal-rich GCs pressure-supported? a little elongated structure Much smaller than giant bulge (R<5 kpc) Disk Thin disk: young GCs, ISM rotating like gas Thick disk: old disk GCs A weaker rotation than the thin disk. Bar: old metal-rich GCs, fast rotation (Morrison+2011) Halo M31 bulge halo disk 18
How to explain the rotation of both old metal-rich and metalpoor GCs in the old view? M31 bulge halo disk 19
Halo structure of M31 M31 has dual halos! Metal-poor (blue) halo pressure-supported, slowly rotating Extended spherical structure (0<R<200 kpc) Metal-rich (red) halo M31 red halo bulge disk blue halo fast rotating Inner elongated structure (0<R<50 kpc) 20
Early type galaxies (Es and S0s) have single spheroidal components (single halos). ETG 21
(Park & Lee 2013, ApJL) Data: GCSs in 23 bright E/S0 galaxies in ACSVCS (Jordan+2009) Ellipticity of the red (metal-rich) GCSs in bright ETGs shows tight correlation with stellar light in their host galaxies, while that of the blue (metal-poor) GCSs does much less. 22
Massive ETGs have dual halos! A blue halo and a red halo. Yin & Yang model? 23
Dual halos in massive ETGs! Red (metal-rich) halos: In the inner region Elongated, rotating Blue (metal-poor) halos: More extended Less elongated, little rotation ETG red halo blue halo 24
Two mode formation Red halo mode Dissipative collapse/merger Blue halo mode Dissipationless merger/accretion Mostly from dwarf galaxies 25
M31 has dual halos! Red halos: In the inner region Elongated, fast rotating Blue halos: More extended Less elongated, slowly rotating ETG red halo blue halo M31 red halo bulge disk blue halo 26
The existence of metal-poor, dynamically hot, slowly rotating halo with no radial gradient, -formed via accretion of dwarfs and GCs The existence of inner metal-rich rotating bulge and red halo with metallicity gradient, -formed via a major merger (and/or monolithic dissipative collapse )? Giant streams and vast thin disk of satellites -formed via major and minor merging Thin disk formed later. In summary, M31 was formed via major merging (with monolithic collapse) and accretion. 27
M31 has dual halos like ETGs. Both metal-rich and metal-poor old GCs are rotating, calling for a theoretical explanation. M31 remains to be intriguing! M31 red halo bulge disk blue halo 28