Stellar-mass Metallicity Relation at High Redshifts - Subaru by pptfiles

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									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
                    ÞEvolution 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,
               Origin of long GRBs       3
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
                We need a           large sample of evolution?
                                                  in chemical

                   SF galaxies at z=1-2!
                             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)
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(?)
                                                             20
                       Ando, KO, et al. 2007, PASJ 59, 717
                      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?



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