Transcript Stellar-mass Metallicity Relation at High Redshifts

Stellar-mass Metallicity Relation
Stellar-mass Metallicity Relation
at High Redshifts
at ｚ～１．4
Near Field Cosmology!?
Extra-galactic Archaeology!
Kouji OHTA （Kyoto University）
K. Yabe, F. Iwamuro, S. Yuma,
M. Akiyama, N. Tamura, FMOS team
et al.
2011年11月2日
1
於 修善寺
Tracing chemical evolution
Lilly et al. 2003, ApJ 597, 730
(CFRS)
Galaxy surveys
Galactic disk stars
Twarog (1980)
Chemical evolution
Evolution of galaxies
and MW Galaxy
But the metallicity here is
for rather bright/massive
galaxies…
2
Mass-metallicity relation
~53,000 SF galaxies at z~0.1
(SDSS)
Tremonti et al.
ApJ 613, 898 (2004)
Need to establish relations at
various redshifts =>
Chemical evolution of galaxies/MW
Even at a fixed stellar mass,
There is a significant scatter
around the relation
=> Physical origin is unknown yet
Related to nature of GRB hosts,
3
Origin of long GRBs
Evolution of mass-metallicity relation
z~0.7: 56 SF galaxies
Savaglio et al. 2005,
ApJ 635, 260
z~2.2: 90 SF galaxies
with Stacking analysis
Erb et al. 2006, ApJ 644, 813
z~3: ~20 SF galaxies
Maiolino et al. 2008, AA 488, 463
Mannucci et al. 2009,
MN 398, 1915
4
Why M-Z relation at z~1.4?
Cosmic SF history
What is the M-Z relation
close to/just after the peak epoch
of cosmic SF history?
=> a major step
in chemical
large sample
of evolution?
We need a
SF galaxiesHow’s
at z=1-2!
the scatter?
=> larger scatter in higher redshifts?
What is the origin of the scatter?
=> key parameter to understand
the evoliution of M-Z relation
(&chemical evolution of galaxies)
Hopkins & Beacom , 2006, ApJ 651, 204
5
Fibre Multi-Object Spectrograph (FMOS)
on Subaru Telescope
• 0.9-1.8um R~700, (R~3000 in HR mode)
• 400 fibres in 30’ FoV
6
Sample
• K(AB) < 23.9 mag in SXDS/UDS
• Stellar mass > 10^9.5 Msun
• 1.2 < z_ph < 1.6
FMOS can cover Hβ -- Hα、[NII]6584
• Expected Hα flux > 1.0x10^-16 erg/s/cm^2
calculated from SFR(UV) & E(B-V)nebular
from UV slope
• Randomly selected ~300 targets
7
Example of spectra
SN >3 for [NII]6584
Typical exp time ~ 3 h
Hα detection: 71 galaxies
3>SN >1.5 for [NII]6584
SN <1.5 for [NII]6584
Metallicity
<= N2 method ([NII]/Hα）
By Pettini & Pagel (2004)
8
AGN rejection
X-ray sources are discarded
(Lx < 10^43 erg/s)
Stacked spectrum w/o AGNs
9
Mass-metallicity relation at z~1.4
SN < 1.5 for [NII]6584
10
• MZ relation locates
between z~0.1 (Tremonti+) and z~2 (Erb+)
(after correcting for the metallicity calibration
& stellar mass (IMF))
• Agree with recent simulation
Galaxy mass dependent
outflow model (vzw)
Dave et al. MN 416, 1354 (2011)
11
Scatter of the MZ relation
• Try to constrain the scatter
• Deviation from the MZ relation
(after removing the obs error)
• Smaller in massive side
• Comparable to z~0.1
• But strictly speaking
they are lower limits
=> Larger scatter at z~1.4
● z~0.1
12
What makes the scatter?
2nd parameter problem at high-z
SFR from Hα
SFR dependence?
SFR>85 Msun/yr
85 >SFR>53 Msun/yr
53 > SFR Msun/yr
SFR – stellar mass relation!
At a fixed mass bin
Relative SFR dependence!
★ higher SFR
☆ lower SFR
Higher SFR => lower metallicity
13
SFR from UV (extinction corrected)
• Same trend
SFR dependence?
SFR>80 Msun/yr
80 >SFR>40 Msun/yr
40 > SFR Msun/yr
SFR – stellar mass relation!
At a fixed mass bin
Relative SFR dependence!
★ higher SFR
☆ lower SFR
Higher SFR => lower metallicity
14
Similar trend at z~0.1
• From SDSS galaxies
• SFR-mass relation
• At a fixed mass, larger
SF comes lower part
Mannucci et al. 2010,
MN 408, 2115
But see Yates et al. 2011
15
Fundamental Metallicity Relation (FMR)
Mannucci et al. 2010, MN 408, 2115
No clear FMR
slight offset
NB:No calibration correction
for the average metallicity
16
Another 2nd parameter: size?
Half light radius
r50 >5.3 kpc
5.3 > r50>4.38 kpc
4.38 > r50
At a fixed mass bin
★ larger r50
☆ smaller r50
Larger galaxy => lower metallicity
similar trend at z~0.1 (Ellison et al.
2008)
17
Cosmological evolution of M-Z relation
Smooth evolution
from z~3 to 0.1
w/o changing shape,
except for massive part
at z~0.1 (saturation?)
(Calibration, stellar mass corrected)
18
Metallicity evolution at Mstellar = 10^10 Msun
- - - : simulation Dave et al. 2011 vzw
19
Metallicity evolution against cosmic age
Rapid
growth
●？
LBGs at z~5
calibration: Heckman et al. 1998
corrected for 0.3 dex for R23(?)
Ando, KO, et al. 2007, PASJ 59, 717
20
Summary
• With FMOS/Subaru
• Establishing M-Z relation of SF galaxies at z~1.4
• Smooth evolution from z~3 to ~0
w/o changing shape of M-Z so much
• Larger scatter at higher redshift?
• Larger SFR => lower metallicity?
• Larger size => lower metallicity?
• More data are necessary to be definitive
• Test for sample selection is also important
• Further studies with a larger sample are desirable!!
21
22
A possible physical cause for the trend
• Infall of pristine gas / merge of a metal poor galaxy
•
dilutes the gas to lower metallicity,
• activates SF,
• expands/enlarges galaxy size
• Really?
23