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KIAA/PKU -- IoA workshop “Near Field Cosmology” Beijing, Dec 1-5, 2008 Star Formation and Chemical Evolution of the Milky Way and M31 Disks Jinliang HOU In collaboration with : Ruixiang CHANG, Jun YIN, Jian FU, Li CHEN, Shiyin SHEN et al. Center for Galaxy and Cosmology Shanghai Astronomical Observatory, CAS A short introduction of our group Astronomical Mansion Shanghai Astronomical Observatory, CAS Star Clusters and the Structure of Galaxies Research interests of the group Structure and evolution of galaxies ---- from the Milky Way to high z galaxies Star clusters and the structure of the Milky Way Galaxy Chemical evolution of the galaxies, high-z galaxies (mainly Damped Lyman Alpha systems) Structure and dynamics of the nearby galaxies Large sample analysis of the nearby galaxies (SDSS, Galex, 2MASS, LAMOST et al. ) Galaxy formation and evolution Staff PhD students: 1. HOU Jinliang 2. CHEN Li 3. SHAO Zhenyi (now in UMASS, USA) 4. CHANG Ruixiang 5. SHEN Shiyin 1. 2. 3. 4. 5. 6. 7. 8. Senior Professors: MS Students: 1. 2. 3. ZHAO Junliang FU Chenqqi WANG Jiaji YIN Jun LIU Chenzhe SHI Xihen GAO Xinhua Wang Caihong GAN Jinalin (now in Heideberg, MPIA), HAN Xuhui (now in Paris Observatoire) FU Jian (now in Munich, MPA) 1. YU Jinchen 2. WANG Youfen Some international collaborators: White S.D.M, Kauffmann G. (MPA) Prantzos N. (IAP) Boissier S. (Observatoire de Marseille) Tytler D. (UCSD) Mo Houjun (UMASS) Levshakov S. (Ioffe Institute of Physical Technique) de Grijs R. (U. Sheffield) Some group members Content Local SFR Law in the Milky Way disk based on abundance gradient evolution Observed differences between M31 and MW disks Model comparisons between M31 and Milky Way disks Summary Local SFR Law in the Milky Way disk based on abundance gradient evolution Kennicutt Law --- average properties Strong correlation between the average gas mass surface density and SFR density for nearby disk and starburst galaxies (Kennicutt 1998) Two types of correlations The later form implies SFR depends on the angular frequency of the gas in the disk. This suggestion is based on the idea that stars are formed in the galactic disk when the ISM with angular frequency Omega is periodically compressed by the passage of the spiral pattern. Applications of Kennicutt SFR law When the Kennicutt law is applied in the detailed studies of galaxy formation and evolution, there are several formulism that often adopted by the modelers : SFR The evolution of abundance gradient along the Milky Way disk Infall SF Law Model A, B Model C Fu, Hou, Chang et al. 2009 Adoption of SFR Law for the chemical evolution model of spiral galaxies 1. For the average properties of a galaxies, KS law is OK 2. For local properties, SFR could be local dependent, a simple description is the introducing of angular velocity (Silk 1997, Kennicutt 1998 ) Observed differences between M31 and MWG M31 and MWG have similar mass and morphology Components in the Milky Way Galaxy dark halo stellar halo thick disk thin disk bulge We would like to understand how our Galaxy came to look like this. The Milky Way, typical or not? It is always regarded that the MWG is the typical spiral in the universe, especially at its mass range. Is this true? How about M31 galaxy, it is a spiral that is comparable with MWG in the Local Group, and now it is possible to have detailed observations. Disk Profiles Total disk SFR MW M31 Yin, Hou, Chang et al. 2009 [O/H] gradient from young objects Two gradients reported: Steep: -0.07 dex / kpc (Rudolph et al. 2006 ) Flat: -0.04 dex/kpc (Deharveng et al. 2000 Dalfon and Cunha 2004) Scaled gradient -0.017 dex / kpc MWD:-0.161 -0.093 M31 :-0.094 MW MW Gas SFR M31 M31 Gas fraction Scaled profiles Model comparisons between M31 and Milky Way disks Purpose of the chemical evolution study for The Milky Way and M31 disks Using the same model • Find common features • Find which properties are galaxy dependent • M31 and MWG, which one is typical ? Model classification Phenomenological Model / Semi-Analytical Model Disk only : One component : Disk (Hou et al.) Two components : Thick Disk + Thin Disk (Chang et al.) Disk+Halo: Two components Three components : Disk +Halo : Thick Disk + Thin Disk + Halo Disk+Halo+Bulge: Three components : Bulge+Disk+Halo Unified One Component Model 1. Disk forms by gas infall from outer dark halo 2. Infall is inside-out 3. SFR: modified KS Law (SFR prop to v/r) M31 disk MW disk 7 1010 3.5 1010 rd (kpc) ( R band) 5.5 2.3 Vflat(km/s) 220 226 Mtot (Ms) Radial Profiles as constrains • • • Gas profile SFR profile Abundance gradient Do the similar chemical evolution models reproduce the global properties for the Milky Way and M31 disks ? SFR M31 gas and SFR in disk Observed of gas and SFR profiles are abnormal when compared with Kennicutt law. Gas and SFR must be modified by some interaction Simulation Observed M32 Block et al. (Nature 2006) Two rings structure Summary : M31 disk properties 1. Current star formation properties are atypical in the M31 disk. Disk formation be affected by interactions 2. Has low SFR in disk shorter time scale for the infall. contradicts the longer infall time scale for halo. Problems Chemical evolution model cannot reproduce the outer profiles of gas surface density and SFR profiles at the same time The observed abundance gradient along the Milky Way disk still not consistent The evolution of gradients is very important. Two tracers : 1. PN (Maciel et al. 2003, 2005, 2006, 2007) and 2. Open Clusters (LAMOST Survey, CHEN Li’s talk, this workshop) Comparison among MW, M31 and M33 MWD M31 disk M33 disk (Yin Jun’s talk ) Infall Quiet Interaction Timescale 7Gyr 7Gyr Slow Accretion 15Gyr Local dependent Modulated by events Local dependent No No Yes Steep/flat ? Flat Steep SFR Outflow Abundance Gradient Thanks Observed difference between M31 and Milky Way galaxies Halo properties Metal - Velocity Tully-Fish Relation SDSS: 1047 edge-on spirals Hammer et al. 2007 Halo properties X X -- M33 Metallicity – luminosity relation Mouhcine et al. 2005 Disk scale length Band Observed scale length ( kpc ) M31 U B V R I K L M31 distance: 785kpc 7.7 6.6 6.0 5.5 5.7 4.8 6.1 the Milky Way 4.0-5.0 2.3-2.8 Note: SDSS average rd = 4.75kpc (Pizagno et al. 2006) Disk specific angular momentum (AM) Hammer et al. 2007 AM prop to rdVrot (Mo et al. 1998) MW is about a factor of 2 less than nearby spirals Observation: which galaxy is a “typical” spiral? Statistical • M31 : metal-rich halo • MWG: metal-poor halo Zibetti et al. (2004) from SDSS survey: 1000 edge-on disc galaxies, metal-rich halo is more common. Harris & Harris (2001) NGC5128 similar to M31 halo Metal-rich seems more common How halo forms ? Why metal-rich ? Does observed halo really halo? Observational constrains in the solar neighborhood • • Find a set of parameters that can best reproduce some observational constrains in the solar neighborhood. Observables of the Milky Way Galaxy 1. MDF (Metallicity Distribution Function) disk and halo 2. [O/Fe] versus [Fe/H] from metal poor to metal rich 3. SFR at present time Physics of the model : Rings independent Gas infall and star formation proceeds in each ring Physical process Solar neighborhood • Gas fraction • Abundance ratio [O/Fe] ~[Fe/H] • G-dwarf metallicity etc. Disk profile • Gas • SFR • Abundance gradients • other global quantities Phenomenological Model Infall Model Halo Disk delayed by tdelay • Two time scales: – h – d depends on the halo formation mechanism as a function of radius, disk formation Star formation: Kennicutt law Halo Disk Chemical evolution Gas depletion Low mass SNIa IMS star SNII Halo and disk Gas of an element i K dwarf Halo Halo : Disk : Disk and halo surface density profile Disk : exponential Halo: modified Hubble law Metallicity Distribution in the MW Disk and Halo Phenomenological Model Infall Model Halo Disk delayed by tdelay • Two time scales: – h – d depends on the halo formation mechanism as a function of radius, disk formation [O/H] gradient from young objects in the Milky Way Disk Rudolph et al. 2006 -0.07 dex / kpc Halo Globular Clusters Number distribution Double peak Number: M31: 700 MW: 162 [Fe/H] gradient from Open Clusters in the Milky Way disk Chen, Hou, Wang (2003) All Open Clusters :age mixed -0.063dex/kpc Summary – 2 : possible correlation between halo Z and Mstar • Model predicts more massive stellar halo in M31, about 6 to 9 times than that of MW halo. • Massive halo has higher metallicity. Bekki, Harris & Harris (2003) simulation : Stellar halo comes from the outer part of the progenitor discs when the bulge is formed by a major merger of two spirals. Correlation between halo metallicity and bulge mass What we can do next for M31 ? • Similar model, at present, we only concentrate on disk • Need to include halo also, a lot of observations are available for the halo, especially in the field of globular clusters. • To add the color evolution, this is important to constrain the model, is it possible to consistent between chemical and color ? • To solve the problem of low gas density in the outer disk, introduce new assumption ? – Higher outer disk SFE ? – Wind in the outer disk ? – Interaction ?