Transcript FIRST LIGHT IN THE UNIVERSE

FIRST LIGHT IN THE UNIVERSE
Saas-Fee, April 2006
Richard Ellis, Caltech
1. Role of Observations in Cosmology & Galaxy Formation
2. Galaxies & the Hubble Sequence
3. Cosmic Star Formation Histories
4. Stellar Mass Assembly
5. Witnessing the End of Cosmic Reionization
6. Into the Dark Ages: Lyman Drop Outs
7. Gravitational Lensing & Lyman Alpha Emitters
8. Cosmic Infrared Background
9. Future Observational Prospects
Motivation
Great progress in tracking comoving star formation history but:
- SF density averages over different physical situations (e.g.
bursts, quiescent phases)
- reliability of measures remains a big concern; no ideal method
- hard to link to theory (witness how CDM is always able to
match the data!)
Stellar mass assembly is a more profound measurement
- here we review how to do it and recent claims that CDM is in
deep trouble
Importance of developing mass diagnostics stressed in several early papers:
Broadhurst et al, Kauffmann et al, Cohen et al, Brinchmann & Ellis
Galaxy masses: what are the options?
Dynamics: rotation & dispersions
(only for restricted populations)
Gravitational lensing
(limited z ranges)
IR-based stellar masses
(universally effective 0<z<6)
K
Einstein Rings
ring arising from single background source
lensing
galaxy
For a compact strong lens aligned with a background source, a ring of
light is seen at a radius depending on the geometry and the lens mass,
i.e. this allows us to measure the mass of the lens (SLACS project)
Total Mass Density Profile
Find total mass profile is isothermal with mass tracing light in shape
and remarkably little evolution in density profile with redshift indicates collisional coupling of gas and DM in ellipticals
The Fundamental Plane:
Empirical correlation between size, L and *
Considerably superior as a
tracer of evolving mass/light
ratio and assembly history:
Dynamical mass:
- no IMF dependence
- Closer proxy for halo mass
Tough to measure:
-  demands high s/n spectra
- large samples difficult
Dressler et al. 1987; Djorgovski & Davis 1987;
Bender Burstein & Faber 1992; Jorgensen et al. 1996
Evolution of the Fundamental Plane (Treu et al 2005)
142 spheroidals: HST-derived scale lengths, Keck dispersions
Increased scatter/deviant trends for lower mass systems?
If
log RE = a log s + b SBE + 
Effective mass
ME   2RE / G
So for fixed slope, change in FP intercept i log (M/L)i
Evolution of the Intercept  of the FP
Strong trend: lower mass systems more scatter/recent assembly
Stellar Masses from Multicolor Photometry
spectral energy distribution
Mass likelihood function
log mass
Spectral energy distribution  (M/L)K
Redshift  LK
hence stellar mass M
log mass
What if you don’t know the redshift?
logM
Expected scatter based on
photo-z error distribution
zspec
Catastrophic errors securing photo-z & masses from same photometry
Bundy et al astro-ph/0512465
What if you only have optical photometry?
A key ingredient in the mass determination is infrared photometry
which is sensitive to the older, lower mass stars; important z > 0.7
BRI vs BRIK
log  (Mopt)
log
MoptMIR
zspec
Bundy 2006 Ph.D. thesis
log  (MIR)
Stellar Masses at z~2 with and without IRAC
Requirement for K-band at z~1 suggests IRAC useful at z > 2
Masses of LBGs @ z~2
Shapley et al 2005 Ap J 626, 698
M(no IRAC) vs M(IRAC)
Effect of Recent SF Bursts on Derived Mass
Weak correlation of mass with long
 luminosity dependent on bursts
Correlation of mass with color
confirms recent activity
important to take into account
15
log
mass
M(4.5m)
Shapley et al 2005 Ap J 626, 698
R-K
Results: Stellar Mass by Morphology
Comoving
mass density
M Mpc-3
Redshift
Early result: the decline in stellar mass in late-types occurs at the
expense of a modest growth in that of regular spirals & ellipticals, i.e.
tranformation (Brinchmann & Ellis 2000 Ap J 536, L77)
Downsizing: SFR & Stellar Mass Density
SFR/volume by mass
Mass/SFR
Low mass galaxies are more active in terms of SFR/stellar mass at
recent times (Juneau et al Ap J 619, L135)
Stellar Mass Assembly by Type in GOODS N/S
• No significant
evolution in massive
galaxies since z~1
• Modest decline with
z in abundance of
massive spheroidals,
most change at lower
mass
• Bulk of associated
evolution is in
massive Irrs
Bundy et al (2005) Ap J
634,977
2dF
(h=1)
Caveat: Dry Mergers?
Caveat: Fundamental Plane measures the
ages of the stars in galaxies of different
masses. Young ages are seen for stars in
low mass galaxies and old ages for stars
in massive galaxies..seemingly in
contrast to hierarchical predictions.
van Dokkum (2005) argues high
preponderance of red tidal features & red
mergers in local samples, coupled with a
postulated increase in merger rate (1+z)m
implies significant mass evolution is still
possible in large galaxies:
i.e. stars could be old but assembled mass
could be younger via self-similar merging
of red sub-units (so-called
`dry
mergers’)
Dry Mergers at High Redshift
Clusters: Tran et al
(astro-ph/0505355)
Field: Bell et
al (astroph/0506425)
No good statistics yet on how prevalent this process is
Palomar-K + DEEP2 Sample
•
•
•
Palomar WIRC 20482 HgCdTe imager: 8.7 arcmin FOV
DEEP2: R < 24.1; 4 fields (incl. EGS, can test cosmic variance)
12,121 DEIMOS redshifts z<1.5 with K<20.0 (1.5 deg2)
•
Goal: explore role of star formation & environment on mass assembly
•
Star formation indicators:
(U-B)0 from CFHT photometry
[OII] equivalent width, DEIMOS spectra (z > 0.7)
•
Environmental density: Use nth spectroscopic neighbor diagnostic with
DEEP2 redshifts (Cooper et al 2005)
Bundy et al (astro-ph/0512465)
Color Bimodality in the DEEP2 Redshift Survey
0.75<z<1.0
Rest U-B
1.0<z<1.40
Rest U-B
Downsizing & Star Formation
• Using rest-frame U-B
color as a discriminant, a
threshold stellar mass is
apparent above which there
is no SF
• Cross-over mass
(red=blue) also increases
with z
• Mass threshold increases
from 1011 M at z~0.3 to
1012M at z >1
• Stable from field-to-field
(V/bin~2.106 Mpc3)
Bundy et al (astro-ph/0512465)
The `Declining Blues’ become the `Rising Reds’
Theoretical Concepts of Feedback
Simulated Disk Merger with AGN Feedback
Mergers fuel AGN which
expel gas and prevent
further star formation
(Springel et al 2004).
AGN feedback arising
from hot gaseous halo
leads to early
suppression of cooling
SF in massive stellar
systems reproducing
`downsizing’ (Croton et al
2005)
age
Massive Galaxies @ z=2: Is CDM in Crisis?
Dickinson et al 2003 HDF-N photo-z
Glazebrook, McCarthy et al 2004 GDDS spectra
Kong et al 2006 pBzK counts
van Dokkum et al 2006 census of z>2 masses
Comparison of Old Semi-Analytic Predictions
Expect strong
decline in
abundance of
massive
spheroidals with
redshift,
But, in detail, the
theoretical
predictions are
very sensitive to
assumed assembly
particularly for
high masses where
mass function is
steep
Munich
Durham

N(>1011Mo) Mpc-3
z
Benson, Ellis & Menanteau MNRAS, 336, 564 (2002)
Dickinson et al (2003) HDF-N
Pioneering study: N=737, H<26.5, zphoto<3, 5 arcmin2
2dF
H=26.5
 SFR(z)
incomplete
 of H-faint low mass galaxies z>1.5
Significant uncertainty estimating contribution
50% of the assembled mass is only in place at a surprisingly low redshift z~1
Integrated SFH underestimates mass assembly: dust, cosmic variance?
Similar HDF-S analysis by Rudnick et al 2003 Ap J 599, 847
Gemini Deep Deep Survey: Stellar Masses
Color pre-selected spectroscopic
sample K<20.6, I<24.5
N=240 in 430 arcmin2 fields
0.5<z<2
BG IMF (~0.55 Salpeter in M/LK)
Surprising abundance of massive
galaxies at z>1.5
Many are `red and dead’
Glazebrook et al Nature 430, 181 (2004)
Gemini Deep Deep Survey: Slow Mass Assembly
Growth rate slower than semi-analytic models (without AGN feedback)
Rate ~independent of mass so problem for M > M10.5 particularly acute
Glazebrook et al Nature 430, 181 (2004)
Census of Stellar Mass 2<z<3
LBG
DRG
FIRES+GOODS+MUSYC: N~300g, 2 < zphoto< 3, 400 arcmin2
Most M>1011M galaxies are DRGs(77%) - LBGs constitute only
17%
No single technique complete in estimating assembly history
van Dokkum et al astro-ph/0601113
Summary of Lecture #4
• Techniques are now well-established for estimating the stellar masses
of galaxies to high redshift; reliability depends on having spectroscopic
redshifts and long wavelength data
• It is now clear that mass assembly since z~2 does not proceed
hierarchically; growth is suppressed in high mass systems at early
times continuing in low mass systems to z~0 (`downsizing’)
• AGN feedback may be able to reproduce this behavior in CDM
models, but further work is needed to understand environmental
dependence of this process: are downsizing trends occurring at a
different rate in clusters vs `field’?
• Massive galaxies are now being found at z>2 in surprising numbers;
many are already passively evolving. This implies much SF activity at
higher redshift