HWR

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III. The Growth of Galaxy Disks and the Evolution
of Galaxy Sizes

• Observed galaxies occupy a small fraction of
  possible structural configurations size, surface
  brightness, shapes, etc..
• Stability?
• Initial Conditions?
• Feed-back during the formation?
• Present-day structural properties
• Observed Evolution of Galaxy Structure
• Comparison to theoretical Expectations

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Present-Day Parameter Relations
ISpheroids/Ellipticals the Fundamental Plane

• Djorgovski and Davis 1987
• Dressler et al 1987
• Joergensen et al 1996
• Any two parameters of
• re,Ie,s
• predict the 3rd well
• Explanation elements
• virial theorem
• quite uniform (M/L)
• stars dominate at center (?)

Joergensen et al 1996
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Present Structural Parameter Relations for Disk
GalaxiesI Disk Size vs Mass/Luminosity

• Galaxy size scales with luminosity/stellar mass
• At given luminosity/size fairly broad (log
  normal) distribution
• RdM1/3

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What determines sizes of stellar disks?

• Angular momentum
• Arising from halo size and spin parameter l
• Dark halo and its adiabatic contraction do matter
• Peebles 69,FallEfstathiou 80
• Conversion of gas to stars
• Toomre64,Kennicutt 98
• Internal re-distribution of angular momentum
• Bar instabilities?
• OstrikerPeebles 73, Norman et al 96
• Direct disk formation simulations
• have been largely unsuccessful
• sub-clump problem
• Katz 91,NavarroSteinmetz 90s,etc..
• Semi-analytic approaches to disk formation
• Dalcanton et al 97,Mo, Mao White 98, van den
  Bosch 99,

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Structural Relations for Disks IIthe
Tully-Fisher (1976) relation

• Tight LB/V vs vcirc relation historically
  exploited for distance estimates
• Tully-Fisher observations to constrain disk
  formation
• Pizagno et al 2005
• Complement SDSS info with Ha rotation curves for
  250 galaxies
• Sample selection
• B/Dmass lt 0.2 all colors

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Tully-Fisher and the structure of disks

• Only need L (or M) to predict Vcirc(2.2Rd) in
  disk systems
• Size does not help to predict Vcirc
• Stellar disks in most galaxies sub-maximal
  v0.6vtot (_at_2.2Rd)

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• Lets use look-back observations
• to tackle disk formation

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Disk evolution with redshift What might we
expect?

• Sizes from Initial Angular Momentum (Fall and
  Efstathiou, 1980)
• Growth of Halos Growth of Galaxies (Mo, Mao and
  White, 1998)
• Rexp(M) M1/3 x l md-4/3jd x
  H(z)-2/3
• When did the presently existing disks form?
• 1/3 of all stars at z0 are in disks
• 40 of all stars (now) have formed since z1
  (mostly in disks)
• Majority of the Milky Way disk stars have formed
  in the last 7Gyrs
• ? z1 ? z0 is the most important epoch for
  building todays stellar disks
• Note higher SFRs at zgt0 ? higher surface
  brightness(?)

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But first some loreDisk Evolution from high-z
to now

• If stellar (disk) sizes reflect
• halo size constant l
• zobservation zformation of halo
• then
• RdH-1(z) for fixed vcirc(halo)
• RdH-2/3(z) for fixed Mass(halo)

Ferguson et al 2004 GOODS

• But what is observed?
• UV-size f(z)
• in UV flux-limited sample
• Agreement likely fortuitous !?

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Observing Galaxy Size Evolution

• How does the currently observed LV-Rd,
  M-Rd, and LV-vc
• evolve with redshift?
• Data Sets
• GEMS 2-band HST imaging 10.000 redshifts
  (Barden et al 2005) 30x previous samples (Lilly
  et al 98 Simard et al 99)
• FIRES JHK imaging (0.45) 6.000 redshifts
  (Trujillo et al 2003/5)
• Data/Analysis Issues
• Understand the (surface brightness) selection
  function well
• Measure sizes at constant rest-frame wavelength
  gt4000A
• Consistent tie-in to z0 data

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Disks to z1 in GEMSSample SelectionBarden, Rix
et al 2005
nlt2.5
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Observed color gradients at z0.5,1.0

• 2-bands HST images in GEMS
• ? check for color-gradients in distant disks
• Same gradients as local
• Correction to rest-frame V is straightforward
• Difference Rd(mass) and Rd(V) is constant with z

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Disk Evolution to z1 from GEMS DataSelection
Function
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How did the surface brightness of disk galaxies
evolve since z1?
Freeman law
brighter

• For luminous galaxies, the mean surface
  brightness has dropped by 1mag over the last 7Gyrs

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Evolution of the mean surface mass density of
disks since z1
Mgt1010Mo
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Redshift Evolution of the Tully-Fisher
RelationBarden, Genzel, Lehnert 2005
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If r(M) is not f(z) ? disks grow inside out
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Now lets extend this type of analysis to
z3(FIRES, Trujillo et al 2003/5)
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Are there sizeable (disk?) galaxies at high
redshift?(Labbe et al 2003 see also Lowenthal
et al 1997)
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Are the FIRES data deep enough?(FIRES data,
Trujillo et al 2003/5)
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V-band Sizes of FIRES Galaxies compared to
SDSS(Trujillo et al 2005Shen et al 2003)
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Size-evolution from z2.5 to z0Trujillo et al
2005
At a given (V-band) luminosity, galaxies were
about 2.5x smaller at z2.5 than now. At a
given stellar mass, they were only 1.4x smaller
than now. Galaxies at high-z were bigger than
the naïve halo-scalings lead us to expect!
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But while NFW halos were denser (within the
virial radius) at high-z, they had lower
concentrations..(Somerville, Rix, Trujillo,
Barden, Bell 2005 in prep.)
Simulated disks _at_ Z3
Z1
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The Role of Bars Should we expect radial
re-distribution due to internal processes?

• How prevalent/strong were bars in the past?
• Claim (Abraham et al 1999)
• Bars only appear at z0.6 (in HDF)
• Analysis of bar frequency in GEMS
• algorithmic bar detection
• Accounting for (1z)4
• local comparison sample

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Bars in GEMSJogee, Rix, et al 2004

• Abundance and strength of bars seems not to have
  changed since z1
• In nSersiclt2.5 selected galaxies
• ? tbar x Nreform gt fbar x tHubble ? bars
  long-lived

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Summary

• spheroids and disks at high-z (0.5-2.5) seem to
  live on the same locus in the M,R,(s) plane
• Evolution of this locus in the LV,R plane,
  reflects changes in stellar mass-to-light ratio
• This argues for galaxies evolving along those
  relations.
• ?(?) disks grow inside out, along R(M)M1/3
• If disks were to grow in mass along with
  their halos, Rd(M) H-1(z) or H-2/3(z),
• we would have expected them to be smaller at
  high-z than observed.

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Open Issues / Next Steps

• Technicalities
• Get more dynamical masses (vz SED masses)
• Exploit the potential of IRAC on Spitzer for
  rest-frame near-IR selection.
• Get much more comprehensive merger rate estimates
• Avenues
• Modelling lagging consideraby behind the wealth
  of new data
• Look-back studies of the environments role in
  galaxy evolution.
• Host galaxies at high-z (vs normal) a key to
  understanding BH growth

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