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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