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					Galaxy Evolution




   Galaxies Block Course March 09
               Eric Bell
The Evolution of the Cosmic Star
        Formation Rate
•   When did it start / ramp up?
•   When were half of the stars formed?
•   Can it be understood (in terms of models)?
•   When/how did the first stars form?

• Estimating the “cosmic star-formation rate”
    – Estimating the SFRs in individual objects
    – Are all relevant sources included
       • Faint
       • Obscured

                      Galaxies Block Course March 09
                                  Eric Bell
SFR vs. SFH




     Borch et al. 2006

Galaxies Block Course March 09
            Eric Bell
 Modeling/interpreting the <SFR>(z)
• The <SFR> = f(z,Mhalo) is a consequence of
  – Fluctuation/halo growth
  – Gas cooling in those halos (cold fuel supply)
  – [feed-back]

• Simulation approaches
  – Direct cosmological hydro-dynamical simulations
      (e.g. Springel and Hernquist 2005)
      • Main issues: resolution + star-formation (+feedback ‘recipe’)

  – Semi-analytic models
     (Kauffmann; Lacey and Cole ’93  Croton et al 06, Somerville et al 08)
      • DM halo abundance and merging from Press-Schechter Theo.
      • Main issues: galaxy merging, spatial information, + star-
        formation (+feedback ‘recipe’)

                          Galaxies Block Course March 09
                                      Eric Bell
       Elements of the Modelling
•   http://www.daf.on.br/etelles/lectures/lacey-2.pdf




               Galaxies Block Course March 09
                           Eric Bell
Galaxies Block Course March 09
            Eric Bell
Galaxies Block Course March 09
            Eric Bell
Galaxies Block Course March 09
            Eric Bell
           Results of such simulations
            1st example: Springel & Hernquist 03



Different assumptions 
different <SFR>(z)                          There are plausible (not unique)
                                            approaches to SF and feed-back
No feed-back  stars for too                descriptions that match <SFR>(z)
early (and too many of them)




                      Galaxies Block Course March 09
                                  Eric Bell
                                              Comparison data—models
                                                    (Somerville et al 08)
                                                                                   No feed-back  vast
                                                                                   overprediction of stars
                                                                                   at all halo masses
Log(fraction) of baryons that have ended up
(at z~0) as stars in halos of mass Mhalo

                                                                                    No AGN feed-back 
                                                                                    overprediction of stars
                                                                                    at HIGH halo masses



                                                                                       Observational constraint
                                                                                       (from B. Moster)




                                                  Galaxies Block Course March 09
                                                              Eric Bell
Now .. How did star-formation start at all in the cosmos?
           (Tom Abel, Greg Bryant, Volker Bromm etc..)




                   Galaxies Block Course March 09
                               Eric Bell
Galaxies Block Course March 09
            Eric Bell
                  Predictions I
• Almost all galaxies
  have gas cooling -
  -> star
  formation…
  – Davé et al.


• Natural state of
  all galaxies is to
  form stars…

                  Galaxies Block Course March 09
                              Eric Bell
                   Predictions II

Dynamical assembly
history - a probe
largely of DM and baryons
  = disks, conservation AM
  = spheroids, mergers/int                              QuickTime™ an d a
                                                   YUV420 codec decompressor
                                                  are need ed to see this p icture .




                                             Matthias Steinmetz, AIP


                       Galaxies Block Course March 09
                                   Eric Bell
What does the Universe
      really do?
                QuickTime™ and a
       TIFF (Uncompressed) decompressor
          are neede d to see this picture.




        Galaxies Block Course March 09
                    Eric Bell
                  Observation
• Blanton+03

• Strong
  bimodality in
  color-
  magnitude
  relation




                  Galaxies Block Course March 09
                              Eric Bell
                     Observation
• Bimodality in color
  space --> narrow
  distribution in SFR/M*
  (blue galaxies) with tail
  towards low SFR/M*
  (red sequence)

• Schiminovich+ 2008




                      Galaxies Block Course March 09
                                  Eric Bell
Key observation : correlation between structure and
                     star formation history
•   A bimodal galaxy                     Blanton et al. 2003; ApJ, 594, 186
    population - transition
    mass of 3e10




                                                                                                                                      Red, non SF
     – Red sequence
         • Mostly non-star-forming
         • Bulk of galaxies bulge-
                                                                                                    QuickTime™ an d a
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           dominated
         • Most massive galaxies




                                                                                                                                      Blue, forms stars
     – Blue cloud
         • Star-forming




                                                    TIFF (Uncompressed) decompressor
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                                                             QuickTime™ and a
         • Bulk of galaxies disk-
           dominated
         • Lower mass galaxies
                                                 Low mass                                                                        High mass


                                                   -18 -20 -22
                                                  Absolute magnitude in i-band
         Cessation (quenching) of star formation is empirically correlated with
                       the existence of a prominent spheroid
                        Galaxies Block Course March 09
                                    Eric Bell
Red correlates with environment…




                                         Mean overdensity



                   Mean overdensity




        Galaxies Block Course March 09
                    Eric Bell
              Story so far…
• Cooling/SF/stellar feedback cannot make a
  red sequence
  – 1/2 of all stellar mass today!
  – Primarily concentrated spheroidal galaxies
  – Correlated also with environment…




                 Galaxies Block Course March 09
                             Eric Bell
Spheroids vs. black holes…

 Black hole mass-
 bulge mass
 correlation

 Scatter <0.3 dex                               QuickTime™ an d a
                                       TIFF (Uncompressed) decompressor
                                          are need ed to see this picture .

 Possibility of a
 link between bulge
 formation and
 BH formation
                                                       Häring and Rix 2004




               Galaxies Block Course March 09
                           Eric Bell
                Story so far…
• Cooling/SF/stellar feedback cannot make a
  red sequence
  – 1/2 of all stellar mass today!
  – Primarily concentrated spheroidal galaxies
     • Because of black holes?
     • AGN feedback?
  – Correlated also with environment…




                   Galaxies Block Course March 09
                               Eric Bell
     Some empirical progress…
• Study how red sequence evolves

• Try to split structure vs. environment

• Is a bulge an absolute requirement for
  shutting off star formation?




               Galaxies Block Course March 09
                           Eric Bell
Evolution of the red
     sequence
               QuickTime™ and a
      TIFF (Uncompressed) decompressor
         are neede d to see this picture.




       Galaxies Block Course March 09
                   Eric Bell
Evolution of red sequence z=1 to today…




                                     Bell et al. 2004




    Galaxies Block Course March 09
                Eric Bell
       Mass function: color split
                     Blue cloud
                                                          Local MFs
                   Red sequence

Weak evolution
in blue guys
(= disks)

Strong evolution
in red guys at                                             Borch et al.
L<2L* at least                                                2006
(= spheroids)




                         Galaxies Block Course March 09
                                     Eric Bell
               Stellar mass density red/blue
                                                Borch et al. 2006
•   Always a pronounced blue
    cloud
    – Color redder with time
                                               Red sequence         Chen et al. 03
•   Red sequence builds up
    with time
    – Color of ancient stars at
      every epoch
    – Build-up of x3 or so
      since z~1 (Bell et al.                   Blue cloud
      2004; Chen et al. 2003;
      Willmer, Faber et al.
      2006)
    – In agreement with at
      least some models (Cole
      et al. 00; Somerville et
      al. 2008)


                       Galaxies Block Course March 09
                                   Eric Bell
               Where’s the mass?
• A red sequence
  –   Dominated by spheroids at z<1
  –   Color evolves ~ passively
  –    stellar mass density increases by x2 or more
  –   Most mass is in spheroids at redshifts below ~0.7

• A blue cloud
  – Dominated by disks
  – Color reddens towards present day
  – Stellar mass function more or less constant since z~1




                     Galaxies Block Course March 09
                                 Eric Bell
         Environment?
• g-r vs. stellar mass
  – Weakly dependent on halo mass
    (bottom panel)
  – Weakly dependent on radius
    (centre panel)
• Stellar mass is a much more
  important driver of properties
  than halo mass
  – Weak residual trend towards
    redness for more massive clusters
    (small radii)
                         Van den Bosch et al. 2008
                Galaxies Block Course March 09
                            Eric Bell
          Bulges
                QuickTime™ and a
       TIFF (Uncompressed) decompressor


A necessary condition for
          are neede d to see this picture.




       quenching?

        Galaxies Block Course March 09
                    Eric Bell
     Bulges: a necessary condition for
                quenching?
• In AGN feedback paradigm, only way for a
  central galaxy to stop gas cooling is
  through AGN feedback
  – Need bulge


• Are there any red central galaxies without
  bulges?




                 Galaxies Block Course March 09
                             Eric Bell
                                 SDSS DR2

                                 NYU VAGC
                                 Blanton+05

                                 Group catalog
                                 Yang et al 05

                                 SF/AGN
                                 Brinchmann+04




                                 Bell 2008




Galaxies Block Course March 09
            Eric Bell
Galaxies Block Course March 09
            Eric Bell
Galaxies Block Course March 09
            Eric Bell
                                              Many red
                                              sequence
                                              n<1.5 have
                                              AGN

                                              * Internally-
                                              driven
                                              transform
                                              Sd-Im to Sph
                                              unlikely
                                              (predict all
                                              Sph satellites)




             Galaxies Block Course March 09
Bulge (SMBH) requirement for quenching for central galaxies
                    Eric Bell
  Closing remarks
               QuickTime™ and a
      TIFF (Uncompressed) decompressor


What does this all mean?
         are neede d to see this picture.




       Galaxies Block Course March 09
                   Eric Bell
                         Summary
• Halo formation, cooling, star formation and stellar feedback
   – Star forming galaxies
   – Mix of spheroid-dominated and disk-dominated


• Observations
   – Almost all spheroid-dominated galaxies are red, non-star-
     formers
   – Not primarily environmental
   – Bulge is a necessary but not sufficient condition for quenching;
     suggests AGN feedback




                       Galaxies Block Course March 09
                                   Eric Bell
    Can AGN feedback work in
           practice?
• Implementation in models
  – Quasar mode (Kauffmann & Haehnelt 2000)
     • Powerful outflow evacutes gas and quenches star
       formation immediately (not clear required by
       observations)
  – Radio mode (Croton et al. 2006)
     • Heating of hot gas envelope of galaxies stops further
       gas cooling
     • Very successful qualitatively
     • Particularly effective when have hot gas as working
       surface (Dekel, Cattaneo)
  – P. Hopkins et al. 2006-present

                   Galaxies Block Course March 09
                               Eric Bell
   Quasar mode feedback?

• Tremonti et
  al 2007 find
  high velocity
  outflows in
  post starburst
  (also post-
  AGN) systems




             Galaxies Block Course March 09
                         Eric Bell
Radio mode feedback?
• Perseus cluster; bubbles and sound
  waves associated with hot gas
  bubbles blown by AGN jets… Fabian
  et al.




                                   QuickTime™ and a
                          TIFF (Uncompressed) decompressor
                             are need ed to see this picture.




       Galaxies Block Course March 09
                   Eric Bell
               AGN feedback
• mergers feed central
  black hole, giving rise
  to an ‘Active Galactic
  Nucleus’ (AGN)
• very efficient
  conversion of rest-
  mass to energy!
• this energy can couple
  to the cold gas in the
  galaxy & may drive
  powerful winds


                                  Di Matteo, Springel & Hernquist 2005
                  Galaxies Block Course March 09
                                    Hopkins et al. 2005, 2006
                              Eric Bell
                                               What happens when we include these
                                               processes in a cosmological simulation?
                       AGN feedback
                       suppresses cooling
                       in massive halos
stellar mass




                                                   z=0 stellar mass function




        supernova-driven winds
        suppress star formation in
        low-mass halos
                                         mass
                             host haloBlock Course March 09
                                Galaxies
                                           Eric Bell
                      models without AGN feedback do not reproduce
                      the slope of the ‘red sequence’ or the color
                      bimodality
                       red dot: spheroid
                       blue dash: disk
                       cyan star: merger




                                  GEMS
                                  data                     model


                     Galaxies Block Course March 09
                                 Eric Bell      faint        bright
rss et al. in prep
                                 model with AGN feedback:
                                 massive, spheroid dominated galaxies have a
                                 massive BH, which is able to release enough
                                 energy to remove the gas from the galaxy and
                                 quench further star formation.




                                         GEMS
Somerville et al. 2009
                         Galaxies Block Course March 09
                                     Eric Bell
                              Summary
•   Halo formation, cooling, star formation and stellar feedback
     – Star forming galaxies
     – Mix of spheroid-dominated and disk-dominated

•   Observations
     – Almost all spheroid-dominated galaxies are red, non-star-formers
     – Not primarily environmental
     – Bulge is a necessary but not sufficient condition for quenching; suggests
       AGN feedback

•   Modelling AGN feedback
     – Quasar mode possibly important
     – Radio mode is likely to be vital
     – Qualitative successes, quantitative success is likely far off




                           Galaxies Block Course March 09
                                       Eric Bell

				
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posted:12/12/2012
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