Dissecting the Red Sequence: Star Formation Histories

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Dissecting the Red Sequence Star Formation
Histories Mass to Light Ratios
Genevieve J. Graves University of California,
Santa Cruz with Sandra Faber Ricardo Schiavon
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binning ? and ?Mdyn/L
at fixed ?, Re variations in Ie ? variations in
Mdyn/L
bin by ? and ?Mdyn/L
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the metallicity hyperplane
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MHP maps onto FP X-section
(Age, Fe/H) (?, ?Mdyn /L)
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variations in Mdyn /L within Re
stellar population (age, Z)
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dynamical mass estimator
SAURON Survey
SLACS Survey
Cappellari et al. (2006) - IFU data, dynamical
models
Bolton et al. (2007) - strong lensing
UW May 27, 2008
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variations in Mdyn /L within Re
stellar population (age, Z)
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the metallicity hyperplane
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M?/L vs. Mdyn /L
Mdyn / L
(SSP)
log Mdyn / L
log M / L
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variations in Mdyn /L within Re
stellar population (age, Z)
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two tilts of the FP
FP midplane
Stellar Population M?/L
log Re
M?/L ? ?
residual tilt Mdyn / M?
log Re
log ?
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M?/L vs. Mdyn /L
Mdyn / L
log Mdyn / L
log M / L
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observational conclusions

• ETG star formation histories 2-D parameter
  space
• (variations with ? and with ?Mdyn/L)
• 2-D family of star formation histories
  X-section of FP
• Stellar population effects cannot account for
  observed tilt
• of the FP, or the observed thickness of the FP
• variations in the IMF or central DM fraction
  required
• high Mdyn/M? correlated with short duration
  star formation
• The two tilts of the FP
• Stellar population effects (M?/L) and variable
  IMF or DM
• fraction (Mdyn/M?) tilts rotate the FP around
  different axes

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variations in the IMF?
more at low end
M/L from Chabrier IMF
need some galaxies with higher M/L
M log (dN / d log M)
more at high end
high end more attractive to match Mg/Fe
0.1 1 10 100
log M (M?)
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variation in DM fraction?
? Mdyn /L is measured within Re

• genuine lack of stellar mass for given halo
  mass
• (low star formation efficiency)
• - early truncation of star formation through
  quenching?
• (by AGN or massive halo)
• redistribution of stellar and dark matter
  inside/outside Re
• - gas-rich vs. dry mergers?

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low sf efficiency halo quenching?
early quenching low Ie, high Mdyn/L
Cattaneo et al. (2008)
late quenching high Ie, low Mdyn/L
naturally produces correlation between Mdyn /L ,
short duration star formation _at_ fixed ?
0 2 4 6 8
z
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low sf efficiency AGN feedback?
Galaxy w/ Powerful Radio Jets _at_
z2.4 OIII?5007 emission aligned w/
radio lobes large outflow velocities
outflow mass-loading and lifetime can carry out
few x 1010 M?
SF truncated in high Mdyn/L objects
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redistribution of stars?
gas fraction of major-merger changes Mdyn / M?
gas fraction
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0.2 dex
fgas varies w/ mass ? contributes to FP tilt
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log Mdyn / M?
could also have fgas variations _at_ fixed ? ? FP
thickness
long-duration SF ? gas-rich mergers
R / Re
Robertson et al. (2006)
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future work

• test variable IMF vs. variable DM fraction
• - look at galaxy cores where DM should be
  unimportant
• - look for central starburst contribution from
  gas-rich merger
• (2-component galaxy light profiles)
• chemical evolution models
• - what forms of variable IMFs match both Mdyn/M?
  and Mg/Fe?
• the role of environment
• - both merger and massive halo explanations
  imply environment
• plays a role
• - relations for central galaxies vs.
  satellites

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M?/L vs. Mdyn /L
Mdyn / L
(SSP)
log Mdyn / L
log M / L
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M?/L from Age, Fe/H