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 年 11 月 2 日 於 修善寺 Near Field Cosmology!? Extra-galactic Archaeology! 1

Tracing chemical evolution Galactic disk stars Twarog (1980) Galaxy surveys Chemical evolution  Evolution of galaxies and MW Galaxy But the metallicity here is for rather bright/massive galaxies… Lilly et al. 2003, ApJ 597, 730 (CFRS) 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, 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 4

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! 5

Fibre Multi-Object Spectrograph (FMOS) on Subaru Telescope um 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 Typical 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) 9

Mass-metallicity relation at z~1.4 SN < 1.5 for [NII]

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? 2 nd parameter problem at high-z 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 Hα

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

Fundamental Metallicity Relation (FMR) Mannucci et al. 2010, MN 408, 2115 NB:No calibration correction No clear FMR slight offset for the average metallicity 16

Another 2 nd 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 (Calibration, stellar mass corrected) Smooth evolution from z~3 to 0.1 w/o changing shape, except for massive part at z~0.1 (saturation?) 18

Metallicity evolution at Mstellar = 10^10 Msun : simulation Dave et al vzw 19

Metallicity evolution against cosmic age ●？●？ Ando, KO, et al. 2007, PASJ 59, 717 LBGs at z~5 calibration: Heckman et al corrected for 0.3 dex for R23(?) Rapid growth 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

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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? 23