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Stellar-mass Metallicity Relation at High Redshifts

Stellar-mass Metallicity Relation at ｚ～ １． 4. Stellar-mass Metallicity Relation at High Redshifts. 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

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Stellar-mass Metallicity Relation at High Redshifts

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  1. Stellar-mass Metallicity Relation at ｚ～１．4 Stellar-mass Metallicity Relation at High Redshifts 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 於修善寺

  2. 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…

  3. 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

  4. 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

  5. Why M-Z relation at z~1.4? 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! Hopkins & Beacom , 2006, ApJ 651, 204

  6. Fibre Multi-Object Spectrograph (FMOS) on Subaru Telescope • 0.9-1.8um R~700, (R~3000 in HR mode) • 400 fibres in 30’ FoV

  7. 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

  8. Example of spectra SN >3 for [NII]6584 Typical exp time ~ 3 h Hαdetection: 71 galaxies 3>SN >1.5 for [NII]6584 SN <1.5 for [NII]6584 Metallicity <= N2 method ([NII]/Hα） By Pettini & Pagel (2004)

  9. AGN rejection X-ray sources are discarded (Lx < 10^43 erg/s) Stacked spectrum w/o AGNs

  10. Mass-metallicity relation at z~1.4 SN < 1.5 for [NII]6584

  11. 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)

  12. 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

  13. 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

  14. 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

  15. 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

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

  17. 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)

  18. 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)

  19. Metallicity evolution at Mstellar = 10^10 Msun - - - : simulation Dave et al. 2011 vzw

  20. 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

  21. 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!!

  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?

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