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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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