Transcript 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.

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 ?