Dissecting the Red Sequence: Stellar Population Properties in Fundamental Plane Space

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Dissecting the Red Sequence Stellar Population
Properties in Fundamental Plane Space
Genevieve J. Graves, S. M. Faber University of
California, Santa Cruz with Ricardo Schiavon
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early type galaxy evolution
?CDM hierarchical formation (small things form
first)
Downsizing massive galaxies are old,
star formation moves to smaller galaxies

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zoo of ETG scaling laws
Early Type Galaxy (ETG) scaling laws
Fundamental Plane Color - Magnitude Mg -
? Metallicity - Luminosity M /L - L etc
structure vs. stellar populations
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ETG structurethe fundamental plane
Jorgensen et al. (1996)
Virial Thm GM / Re ? ?2 M ? ?2 Re
Definition Ie ? L / ?Re2 L ? Re2 Ie
?2 Re ? Re2 Ie Re ? ?2 Ie-1
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Age-metallicity hyperplane
Trager et al., AJ, 120, 165, 2001 50 local
ellipticals
Metal-rich gtgt
High-S/N spectra from Gonzalez (1993)
Age and Z from H?, Mg b, Fe5270, and F5335
Lines of constant ?
Older gtgt
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Color-mag-? hyperplane
Color-magnitude relation
Color-? relation
?-magnitude relation
Graves, Faber Schiavon (2008c, ApJ, in press)
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zoo of ETG scaling laws
Early Type Galaxy (ETG) scaling laws
Fundamental Plane Color - Magnitude Mg -
? Metallicity - Luminosity M /L - L etc
structure vs. stellar populations
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ETG sample selection
Our sample 16,000 SDSS early type galaxy
spectra
0.04 lt z lt 0.08 no emission! ( lt 2?
in H? and OII ) concentrated light
profile ( R90 / R50 gt 2.5) no color
selection
red
blue
spectra S / N 20 Å-1
bright
faint
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binning galaxies in FP space
sort galaxies into bins stack spectra of
galaxies in each bin determine age, Fe/H,
Mg/H, Mg/Fe
log Ie
Graves, Faber Schiavon (2008a, submitted to
ApJ)
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stellar pops along the FP
view of fp approx face-on
log Re
log Re
Graves, Faber Schiavon (2008a)
log ?
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stellar pops along the FP
faint medium brtight
faint
mid
bright
H?, ltFegt, Mg b Age, Fe/H, Mg/Fe
log Re
log Re
star formation history is independent of Re
log Re
Graves, Faber Schiavon (2008a)
log ?
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stellar populations along the fp
Graves, Faber Schiavon (2008a)
UW May 27, 2008
Nelan et al. 2005
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stellar populations along the fp
Graves, Faber Schiavon (2008a)
UW May 27, 2008
Nelan et al. 2005
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interpretation
log Age
Higher-? galaxies are

• older (downsizing)
• more metal-rich (deeper
• potential wells)
• enhanced in ?-elements relative
• to solar (shorter star formation
• timescale)

Z/H Mg/H
?/Fe Mg/Fe
Nelan et al. (2005)
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stellar populations along the fp
Graves, Faber Schiavon (2008a)
UW May 27, 2008
Nelan et al. 2005
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stellar pops thru the FP

• _at_ fixed ?, galaxies
• with higher Ie have
• younger ages
• higher Fe/H
• lower Mg/Fe

?log Ie is local residual above or below plane at
fixed Re and ?
Graves, Faber Schiavon (2008a)
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stellar populations across the fp

• _at_ fixed ?, galaxies
• with lower Mdyn /L have
• younger ages
• higher Fe/H
• lower Mg/Fe

GG, Faber Schiavon (2008a)
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age-metallicity hyperplane
Graves, Faber Schiavon (2008b)
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MHP maps onto FP X-section
(Age, Fe/H) (?, ? logIe)
?logIe
?
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MHP maps onto FP X-section
(Age, Fe/H) (?, ? logIe)
?logIe
?
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MHP maps onto FP X-section
(Age, Fe/H) (?, ? logIe)
?
?logIe
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MHP maps onto FP X-section
(Age, Fe/H) (?, ? logIe)
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toy star-formation model
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conclusions

• ? We have mapped stellar population properties in
  3-D FP space
• Stellar pops can be inferred (on average) from
  easily measured
• structural parameters
• ? Stellar populations vary with ? but not Re
  along the FP
• 2-D family of star formation histories maps to
  X-section of FP
• - Younger, brighter stellar pops above older,
  dimmer pops below
• The two underlying population parameters may be
  the mean
• epoch of SFR and the duration of SFR

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four questions

• Why are stellar populations independent of R?
  This is not
• true of spiral galaxies today. It is also
  not predicted by current SAMs.
• 2) Why is the transition smooth between the
  E-dominated red sequence and the S0-dominated red
  sequence?
• Will the picture change when LINERS and
  Transition galaxies are added?
• How much do galaxies scatter inside each bin?

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2-D family of star formation
at fixed ?, lower Ie galaxies have shorter
star formation timescales
Age ? Fe/H ? Mg/Fe ?
Age ? Fe/H ? Mg/Fe ?
? Ie
More massive galaxies (higher ?) form
stars at earlier times retain metals (Fe,
Mg) form stars rapidly
?
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