hwr princeton, 2005 iii. the growth of galaxy disks and the evolution of galaxy sizes observed...

HWRPrinceton, 2005

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

HWRPrinceton, 2005

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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