Stellar-mass Metallicity Relation at High Redshifts
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Transcript of Stellar-mass Metallicity Relation at High Redshifts
Stellar-mass Metallicity Relation at High Redshifts
Stellar-mass Metallicity Relation at z~1. 4
Kouji OHTA ( Kyoto University )K. Yabe, F. Iwamuro, S. Yuma, M. Akiyama, N. Tamura, FMOS team et al. 2011 年 11 月 2 日於 修善寺
Near Field Cosmology!?Extra-galactic Archaeology!
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Tracing chemical evolution
Galactic disk stars Twarog (1980)
Galaxy surveys
Chemical evolutionÞEvolution of galaxies and MW Galaxy
But the metallicity here isfor rather bright/massive galaxies…
Lilly et al. 2003, ApJ 597, 730 (CFRS)
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Mass-metallicity relation~53,000 SF galaxies at z~0.1(SDSS) Tremonti et al. ApJ 613, 898 (2004)
Need to establish relations atvarious 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,Origin of long GRBs 3
Evolution of mass-metallicity relation
Mannucci et al. 2009, MN 398, 1915
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
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Why M-Z relation at z~1.4?
Hopkins & Beacom , 2006, ApJ 651, 204
What is the M-Z relation close to/just after the peak epoch of cosmic SF history? => a major step in chemical evolution?
How’s 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)
Cosmic SF history
We need a large sample of SF galaxies at z=1-2!
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Fibre Multi-Object Spectrograph (FMOS) on Subaru Telescope
• 0.9-1.8um R~700, (R~3000 in HR mode)
• 400 fibres in 30’ FoV
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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
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Example of spectraTypical exp time ~ 3 h Hα detection: 71 galaxies
SN >3 for [NII]6584
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
Stacked spectrum w/o AGNs
X-ray sources are discarded(Lx < 10^43 erg/s)
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Mass-metallicity relation at z~1.4SN < 1.5 for [NII]6584
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• 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)
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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
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What makes the scatter?2nd parameter problem at high-z
SFR dependence? SFR>85 Msun/yr 85 >SFR>53 Msun/yr 53 > SFR Msun/yrSFR – stellar mass relation!
At a fixed mass binRelative SFR dependence!★ higher SFR
☆ lower SFR
Higher SFR => lower metallicity 13
SFR from Hα
SFR from UV (extinction corrected)
• Same trend
SFR dependence? SFR>80 Msun/yr 80 >SFR>40 Msun/yr 40 > SFR Msun/yrSFR – stellar mass relation!
At a fixed mass binRelative 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
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Fundamental Metallicity Relation (FMR)Mannucci et al. 2010, MN 408, 2115
NB:No calibration correction
No clear FMRslight offset 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)
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Cosmological evolution of M-Z relation
(Calibration, stellar mass corrected)
Smooth evolution from z~3 to 0.1w/o changing shape,except for massive partat z~0.1 (saturation?)
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Metallicity evolution at Mstellar = 10^10 Msun
- - - : simulation Dave et al. 2011 vzw 19
Metallicity evolution against cosmic age
● ?
Ando, KO, et al. 2007, PASJ 59, 717
LBGs at z~5 calibration: Heckman et al. 1998corrected for 0.3 dex for R23(?)
Rapid growth
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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!!
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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?
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