Chap.3 The nature of Galactic components Overview of (old) Galactic components bulge, thick disk, metal-weak halo Globular clusters metallicity & age distribution Satellite galaxies spatial and metallicity distributions 1 Old components in the Milky Way globular cluster halo star thick disk age > 10 Gyr (formation redshift > 2) Bulge Halo age > 10 Gyr (formation redshift > 2) Fossil records in Galaxy formation Near-field Cosmology 2 3.1 Galactic bulge bulge+disk disk Large ISM extinction IR Obs 1Gyr isochrone Bulge stars in the NIR CM-diagram (using photometric data) bulge Zoccali et al. 2003, A&A, 399, 931 Zoccali et al. 2003 HB 10Gyr isochrone at overall metallicity [M/H]=-1.3, 0.0 3 & 5 Gyr isochrone at [M/H]=-1.3, 0.0 3 4
Distributions of [Fe/H] and [Mg/Fe] in Galactic Bulge Bensby et al. 2013 Alves-Brito et al. 2010 (for RGBs) -elements for bulge/disk dwarfs (Bensby et al. 2013) Filled grey: bulge Red: thick disk Blue: thin disk Bulge stars show COBE image Age distribution for bulge dwarfs (Bensby et al. 2013) BRAVA (Bulge Radial Velocity Assay) Howard+ 2009 7 COBE 2 m image BRAVA survey fields Spheroid Bar * Cylindrical rotation * No classical bulge with hot dynamics 8 5
3D structure of a boxy/peanut shape bar Athanassoula (2005) Edge-on Orbits in a bar Face-on Galactic Bulge: summary Old age ~ 10 Gyr Broad metallicity distribution function (MDF) -1 < [Fe/H] < 0, metal-rich stars are dominant. Alpha enhanced Enrichment by Type II SNe (time scale < 1 Gyr) Boxy/peanut shape with cylindrical rotation Resembling 3d dynamical structure of a bar (pseudobulge) which formed via disk instability (made of old disk stars) No or small fraction of a classical bulge (via major merger) Bulge formation by disk instability? 10 3.2 Galactic disk Metallicity distribution of nearby stars Geneva-Copenhagen Survey Thick-disk-to-thin-disk probability ratio (from stellar kinematics) Spectroscopic sample used in Bensby+ (2014) For thick-disk stars For thin-disk stars Photometric metallicity Spectroscopic metallicity 11 Gilmore & Reid 1983, MN, 202, 1025 Discovery of the thick-disk component Number density of stars vs z 300pc 1350pc Exponential scale height h z h z R z Thin disk ~0.3 34 18 220 Thick disk ~1.0 61 39 200 12 9
Edvardsson et al. 1993 Quillen & Garnett, astro-ph/0004210 Thick disk stars 13 at [Fe/H] < -0.4, age >10Gyr Feltzing et al. 2003 -disk stars Van der Kruit & Searle 1981 Thick disk in NGC4565 Thick disk Thin disk 14 [alpha-elements/fe] = Type II SNe / Type Ia SNe Chemical clock diagram Thick disk Thin disk Bensby+ 2014 15 Age-Metallicity Relation (AMR) Thick disk F G-dwarfs near the Sun (Bensby et al. 2014) Presence of old but metal-rich stars gives a large dispersion in AMR 16
Comparison with metallicity distribution (MD) of young stars (B-type stars) Feltzing & Chiba (2013) using Nieva and Przybilla (2012) data B stars MD of B-type stars reflects that of ISM near the Sun Very meal-rich stars with [Fe/H] > + 0.2 cannot be formed near the Sun 17 Metallicity distribution of the thick disk (reproduced from Wyse & Gilmore 1995) (Chiba & Beers 2000) fiducial metallicity range of the thick disk -1 < [Fe/H] < -0.4 But the rapidly-rotating disk component is extended toward lower metallicity: Metal-Weak Thick Disk (MWTD) 18 3.3 Galactic halo Ryan & Norris 1991, AJ, 101, 1865 High proper-motion stars [Fe/H] 19 5 Gyr 10 15 Unavane et al. (1996) Halo stars (near the Sun) are old (>10 Gyr). Later accreted fraction < 10% 20
[ /Fe] for Galactic stars (Venn et al. 2004) Halo Thick disk Thin disk Retrograde halo Dwarf satellites 21 (Nissen & Schuster 2010) + thick disk halo 22 Chiba & Beers 2000 Rotational properties of metal-poor stars discontinuity halo -1.7 disk U,V,W velocities of nearby stars V =220 km/s V =0 km/s 23 disk halo 24
GC <0 r Radial anisotropy: - ( 2 + 2 )/2 r 2 K12: Kafle et al. 2012 (using 4664 BHBs from SDSS) Red cross: Deason et al. 2013 (halo stars with HST proper motions) 25 3.4 Globular clusters Zinn 1985, ApJ, 293, 424 Halo clusters, disk (bulge) clusters Zinn 1993, ASP Conf. vol.48 HB morphology 26 6kpc Mackey & Gilmore 2004, MN, 355, 504-1.1Gyr -2.2 Gyr Relative to the age of M92 27 (~ 12.6 Gyr) 28
Bulge/disk Old halo Young halo 29 Clusters in the LMC, SMC, + Fornax and Sgr dwarf galaxies 30 LMC SMC Fornax Sagittarius 31 Lee et al. 1999 EHB: Extended HB CTIO 0.9m Z=0.0004 0.005
Bedin et al. 2004 High helium abundance!? Norris 2004 Na-O anti-correlation in GCs (Carretta+ 2010) general properties of GCs multiple stellar population!? H-burning at high T (CNO, NeNa, MgAl cycle) 1. First-generation stars changed Na & O abundance inside these stars (Na O ) 2. Gas was expelled via. AGB & SN. 3. New-generation stars formed from this processed gas 3.5 Galactic satellites List of bright satellites 36 Scl Car For Leo II Leo I Phe
Leo I Fornax 37 38 Mean [Fe/H] vs. luminosity for dsphs Kirby et al. 2008 More recent results 39 Mass enclosed within stellar extent (~ 4 x 10 7 M ) in dsph galaxies Dark matter dominated! (old data) 40