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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,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

• Rd~M*1/3

Disks

SpheroidsDisks

Spheroids

Shen et al 2003 SDSS

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What determines sizes of stellar disks?

Angular momentumArising from halo size and spin parameter

Dark halo and its adiabatic contraction do matterPeebles ‘69,Fall+Efstathiou ‘80

Conversion of gas to starsToomre’64,Kennicutt ‘98

Internal re-distribution of angular momentumBar instabilities?

Ostriker&Peebles ’73, Norman et al ‘96

Direct disk formation simulations have been largely unsuccessful

“sub-clump” problem Katz ‘91,Navarro&Steinmetz ‘90s,etc..

Semi-analytic approaches to disk formationDalcanton et al ‘97,Mo, Mao & White 98, van den Bosch ‘99,

Naab&Ostriker ‘05

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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

Hrotation curves for 250 galaxies

– Sample selection:

B/Dmass < 0.2; all colors

Pizagno, Weinberg, Rix, et al 2005

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“Tully-Fisher” and the structure of disks

)(2.2 *

*,2.2*, MR

MGV

d

SED

)(2.2 *

*,2.2*, MR

MGV

d

SED

2-param. relation 3-param. relation

“Maximal” disk

•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” v*~0.6vtot (@2.2Rd)

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Let’s 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*) ~ M*1/3 x md

-4/3jd x H(z)-2/3

• When did the presently existing disks form?– 1/3 of all stars at z~0 are in disks– 40% of all stars (now) have formed since z~1 (mostly in

disks)– Majority of the Milky Way disk stars have formed in the last

7Gyrs

z~1 z~0 is the most important epoch for building today’s stellar disks

– Note: higher SFRs at z>0 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 zobservation = zformation of halo

then Rd~H-1(z) for fixed vcirc(halo)

Rd~H-2/3(z) for fixed Mass(halo) Rd~H-1(z)

Rd=const (phys.)

Rd~H-2/3(z)

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 >4000A– Consistent tie-in to z~0 data

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Disks to z~1 in GEMSSample SelectionBarden, Rix et al 2005

n<2.5

That’s our operative definition of disks == low concentration radial profile

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Observed color gradients at z~0.5,1.0

• 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

Redshift slices from GEMS

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Disk Evolution to z~1 from GEMS DataSelection Function

GOODS selection box

(Ravindranath et al 2004)

v=co

nst

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How did the surface brightness of disk galaxies evolve since z~1?

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

MV<-20

1 mag

Freeman “law”

brig

hte

r

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Evolution of the mean surface mass density of disks since z~1

M*>1010Mo

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Redshift Evolution of the Tully-Fisher RelationBarden, Genzel, Lehnert 2005

Expected change in surface brightness from the observed stellar population changes

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If r(M) is not f(z) disks grow inside out

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Now let’s extend this type of analysis to z~3(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)

M81 At the present, “normal” disk galaxies look completely different in the UV than in the optical

Zspec=2.

9

“peculiar”, or star-forming ring seen in the UV

Older / redder bulge / bar?

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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 2005;Shen et al 2003)

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Size-evolution from z~2.5 to z~0

Trujillo et al 2005

At a given (V-band) luminosity,galaxies were about 2.5x smaller at z~2.5 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 leadus to expect!

H2/3(z)

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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 @ Z=3

Z=1

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H2/3(z)

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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 z~0.6 (in HDF)

Analysis of bar frequency in GEMS

•algorithmic bar detection

•Accounting for (1+z)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 z~1

•In nSersic<2.5 selected galaxies

tbar x Nreform > 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,() 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 “environment’s” role in galaxy

evolution.– Host galaxies at high-z (vs normal): a key to understanding

BH growth

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