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 CosmologyShanghai Astronomical Observatory, CAS

A short introduction of our group

Star Clusters and the Structure of Galaxies

Astronomical Mansion

Shanghai Astronomical Observatory, CAS

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 (ma

inly 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

PhD students:

1. YIN Jun

2. LIU Chenzhe

3. SHI Xihen

4. GAO Xinhua

5. Wang Caihong

6. GAN Jinalin (now in Heideberg, MPIA),

7. HAN Xuhui (now in Paris Observatoire)

8. FU Jian (now in Munich, MPA)

MS Students：

1. YU Jinchen

2. WANG Youfen

Staff

1. HOU Jinliang

2. CHEN Li

3. SHAO Zhenyi (now

in UMASS, USA)

4. CHANG Ruixiang

5. SHEN Shiyin

Senior Professors ：

1. ZHAO Junliang

2. FU Chenqqi

3. WANG Jiaji

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

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

Content

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

thin disk

thick 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

Yin, Hou, Chang et al. 2009

Total disk SFR

MW

M31

[O/H] gradient from young objects

－ 0.017 dex / kpc

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

MWD: － 0.161 － 0.093

M31 : － 0.094

Scaled profiles

MW

M31

MW

M31

Gas SFR

Gasfraction

Model comparisons between M31 and Milky Way disks

Purpose of the chemical evolution studyfor 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

Disk only : One component : Disk (Hou et al.) Two components : Thick Disk + Thin Disk (Chang et al.)

Disk+Halo:Two components : Disk +Halo Three components : Thick Disk + Thin Disk + Halo

Disk+Halo+Bulge:Three components : Bulge+Disk+Halo

Semi-Analytical Model Phenomenological Model /

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

Mtot (Ms) 7 1010 3.5 1010

rd (kpc) ( R band) 5.5 2.3

Vflat(km/s) 220 226

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

Block et al. (Nature 2006)

Observed

Simulation

M32 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

Timescale

Quiet

7Gyr

Interaction

7Gyr

SlowAccretion

15Gyr

SFR Local dependent

Modulated by events

Local dependent

Outflow No No Yes

Abundance Gradient

Steep/flat ? Flat Steep

Thanks

Observed difference between M31 and Milky Way galaxies

Hammer et al. 2007

Halo properties

Metal - Velocity

Tully-Fish Relation

SDSS: 1047 edge-on spirals

Mouhcine et al. 2005

Halo properties

Metallicity – luminosity relation

X

X -- M33

Disk scale lengthDisk scale length

Band Observed scale length ( kpc )

M31 the Milky Way

U 7.7 B 6.6 4.0-5.0 V 6.0 R 5.5 2.3-2.8 I 5.7

K 4.8 L 6.1

Note: SDSS average rd = 4.75kpc (Pizagno et al. 2006)

M31 distance: 785kpc

AM prop to rdVrot

(Mo et al. 1998)

Disk specific angular momentum Disk specific angular momentum (AM)(AM)

Hammer et al. 2007

MW is about a factorof 2 less than nearby spirals

Observation: which galaxy is a “typical” spiral?

Statistical

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?

• M31 : metal-rich halo• MWG: metal-poor 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 : Gas infall and star formation proceeds in each ring

Physical process

Disk profile • Gas • SFR • Abundance gradients• other global quantities

Rings independent

Solar neighborhood• Gas fraction• Abundance ratio [O/Fe] ～ [Fe/H]• G-dwarf metallicity etc.

Infall Model

• Two time scales: – h depends on the halo formation mechanism

– d as a function of radius, disk formation

Halo Disk delayed by tdelay

Phenomenological Model

Star formation: Kennicutt law

Halo

Disk

Chemical evolution Gas of an element i

Gas depletion

Low mass

SNIa

IMS star

SNII

Halo and disk

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

Infall Model

• Two time scales: – h depends on the halo formation mechanism

– d as a function of radius, disk formation

Halo Disk delayed by tdelay

Phenomenological Model

[O/H] gradient from young objects in the Milky Way Disk

－ 0.07 dex / kpc

Rudolph et al. 2006

Halo Globular Clusters

Number distribution

Double peak

Number:

M31: 700

MW: 162

[Fe/H] gradient from Open Clusters in the Milky Way disk

All Open Clusters ： age mixed － 0.063dex/kpc

Chen, Hou, Wang (2003)

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 ?