Transcript III. The Growth of Galaxy Disks and the Evolution of Galaxy Sizes Observed galaxies occupy a small fraction of possible structural configurations: size, surface.

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
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•Comparison to theoretical
Expectations
Present-Day Parameter Relations I
Spheroids/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 (?)
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Joergensen et al 1996
Present Structural Parameter Relations for Disk Galaxies
I: Disk Size vs Mass/Luminosity
• Galaxy size scales with
luminosity/stellar mass
• At given luminosity/size:
fairly broad (log normal)
distribution
Disks
Disks
Spheroids
Spheroids
• Rd~M*1/3
Shen et al 2003 SDSS
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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,Fall+Efstathiou ‘80
Conversion of gas to stars
Toomre’64,Kennicutt ‘98
Internal re-distribution of angular momentum
Bar 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 formation
Dalcanton et al ‘97,Mo, Mao & White 98, van den Bosch ‘99,
Naab&Ostriker ‘05
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Structural Relations for Disks II
the “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 < 0.2; all colors
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Pizagno, Weinberg, Rix, et al 2005
“Tully-Fisher” and the structure of disks
2-param. relation
V*, 2.2 
G  M *, SED
2.2  Rd ( M * )
3-param. relation
V*, 2.2 
G  M *, SED
2.2  Rd ( M * )
“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 l 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 lore
Disk Evolution from high-z to now
If stellar (disk) sizes reflect
halo size + constant l
zobservation = zformation of halo
then
Rd~H-1(z) for fixed vcirc(halo)
Rd~H-2/3(z) for fixed Mass(halo)
But what is observed?
•
UV-size = f(z)
in UV flux-limited sample
• Agreement likely fortuitous !?
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Ferguson et al 2004 GOODS
Rd~H-1(z)
Rd~H-2/3(z)
Rd=const (phys.)
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 GEMS
Sample Selection
Barden, Rix et al 2005
That’s our operative
definition of disks
== low concentration
radial profile
n<2.5
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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
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Redshift slices
from GEMS
Disk Evolution to z~1 from GEMS Data
Selection Function
GOODS selection box
(Ravindranath et al 2004)
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How did the surface brightness of disk galaxies
evolve since z~1?
brighter
Freeman “law”
For luminous galaxies, the
mean surface brightness
has dropped by 1mag over
the last 7Gyrs
1 mag
MV<-20
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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 Relation
Barden, 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
“peculiar”, or starforming ring seen in
the UV
Zspec=2.9
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Older / redder
bulge / bar?
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 lead
us to expect!
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H2/3(z)
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.)
Z=1
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Simulated disks @ Z=3
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 GEMS
Jogee, 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,(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 nearIR 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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