The Lure of the Dark and Mysterious:

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The Lure of the Dark and Mysterious Observational
cosmology at UIUC
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The History of the Universe (Compressed by 1016)
Big Bang (Early Universe was hot) Small
primordial fluctuations (inflation?) Perturbatio
ns grow (stars, galaxies, bugs).
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How to Measure Time We dont measure time
directly, only redshift.
Flat FRW cosmology Equation of state
How a(t) is calculated Nonrelativistic
matter w 0 r ? a-3 a ? t 2/3 Relativistic
matter w 1/3 r ? a-4 a ? t 1/2 Dark
energy w -1(?) r r0 a ? e Lt
Matter-DE equality was at z 0.32, about 3.5 Gy
ago.
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Cosmological Phenomenology What is observed
(partial list)
Primordial chemical abundanceProbes z 1010
(when T 0.1 MeV). Cosmic microvave
background (CMB)Probes z 1100 (70, when T
0.3 eV). Galaxy and cluster formationProbes z
10 There is little direct information about
the dark ages, (10 lt z lt 1100).
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Cosmological Parameters Measurements are strongly
correlated.
H(t) Expansion rate, . H2(z) H20 ?m
(1z)3 ?R (1z)4 ?L (1z)3(1w) (?-1)
(1z)2 Critical density, rc
3H2/8pG. W Total energy density (divided by
rc). Determines the geometry (open/closed).
Wb, Wm, WL, etc. Component densities. n P(k)
? k n. (Inflation predicts n ? 1.) s8 Density
amplitude at k 2p/(8 Mpc). t Optical depth
since z 1088. w,w Equation of state of DE.
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Density Perturbations The universe is not quite
homogeneous
What is the origin of fluctuations? Can we
understand their evolution? Power
spectra Expansion of Dx(q,f) in terms of
Ylm. l is converted to k, if distance is
known. x is any quantity on the sky (e.g., CMB
temperature, galaxy density, etc.) 3-D spectra
are just beginning to be done (by, e.g., SDSS).
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Cosmic Microwave Background
The primary result of CMB experiments is the
spectrum of density fluctuations when z 1100 (t
375 ky AB). Two measurements DT (gravitation
al potential at source) Polarization (quadrupole
moment of r(q,f)) Dr/r 10-5, then. These
perturbations grew with time, But not fast
enough to make stars soon. Stars began to form
at z 10-20, before galaxies. The distance
scale for star formation is much smaller (larger
k) The primordial spectrum is ? kn, where n
1. Foreground matter distorts CMB (a problem and
an opportunity).(e.g., Sachs-Wolfe
Sunyaev-Zeldovich effects)
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Dark Matter
Is the dark matter composed of weakly interacting
particles? (supersymmetry)
The density is about right.
The shape of galactic halos is about right.
Does the dark matter self-interact?
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Dark Energy The Cosmological Constant?
The expansion is accelerating (ä gt 0). This means
w -1/3, or WL gt Wm/2. At a given z, a SN
is dimmer if ä gt 0, because it is farther than
if ä 0. ä ? 2WL - Wm Possibilities
Cosmological constant, L. w -1 Dynamics
(e.g., quintessence)w(a) w0 w0 (a-a0)
Wang Tegmark, astro-ph/0403292
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Neutrinos Neutrino mass has cosmological effects.
At least one neutrino has mn ? 0.04 eV. kT0
2.3?10-4 eV, so one n has been nonrelativistic
since at least z 200. Massive neutrinos
contribute to structure, but only on large
distance scales (knr ? mn1/2). Amplitude of
contribution ? Smn. Present limit Smn 0.7
eV (statistics limited).Non-zero result (2.5 s)
claimed by Allen, Schmidt, Bridle, MNRAS 346,
59 (2003).
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Two Cosmology Projects at UIUC HEP, Astronomy,
NCSA
Dark Energy Survey (DES) Upgrade an existing 4
m telescope. Deeper (higher z) than SDSS, but
half the solid angle. Data in 2008. Large
Synoptic Survey Telescope (LSST) Build a new
8.4 m telescope. Deeper than DES, and half the
sky. (x2 SDSS) Data in 2012.
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Dark Energy DES LSST will measure DE four ways
Measure the z dependence of Galaxy cluster
distributions Weak lensing (another way to
measure clusters) Galaxy angular power
spectrum Supernova brightness The first three
methods measure the evolution of structure.
Supernovas probe H(z).
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Dark Energy Survey UIUC, Fermilab, Chicago, LBNL,
CTIO
The Device An upgrade to the existing
Blanco 4 m telescope at CTIO. Build a new
500 Mpixel CCD focal plane. Use 60 2k?4k
SNAP prototype CCDs. Some parameters 2.1
diameter field of view 45 MBps data rate (no
trigger). 1 PB data set 600 nights (4
years) Cost 15M Critical path is CCD
acquisition and testing.
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Galaxy Cluster Distributions
The Initial motivation for DES was optical
follow-up to the South Pole Telescope (SPT).
SPT uses S-Z to measures galaxy clusters, but
S-Z does not determine redshifts. DES will
measure cluster zs by surveying the same sky.
Cluster formation rate is sensitive to DE. Data
set 30,000 clusters and 3?108 galaxies 5000
deg2 (12 of the sky). 2000 supernovas for z lt
0.8. Galaxy z ? 1.1, sz 0.03 (photometric).
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Weak Gravitational Lensing
Observational issues Galaxies arent round.
Statistical analysis. The more galaxies, the
better. Small lens mass ? small shear. Must
control systematics. Best sensitivity requires
source galaxies at twice the distance. DES will
see sources to z 1.1.
DES result, if 20 gal/arcmin2 PSF 0.9
arcsec Hu Jain, astro-ph/0312395
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Galaxy Angular Power Spectrum
We have not completed our analysis, but can scale
from published SDSS results ( 6 of their final
data set). They see 8?106 galaxies, will have
1.3?108. DES will have 3?108. Their z is
lt 0.5 DES to z 1.1. Observational issue
We only measure the visible matter, but some
parameters arent sensitive. Bias does not
seem to be a serious problem on large distance
scales (where only gravity matters).
We think, Smn limit ? 0.15 eV (statistics only).
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Supernovae
About 10 of DES time will be spent repeatedly
scanning 40 deg2 of sky to find 1800 Sne (z lt
0.8) and measure their light curves. This will
be the largest SN sample before LSST
SNAP. Redshift uncertainty will be the largest
source of error, so accurate WL will require
spectroscopic follow-up. Note the parameter
correlations.
Assuming Spectroscopic follow-up
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LSST DOE groups SLAC, LLNL, BNL, UIUC, Harvard
This will be a new telescope, designed for the
science.
Large aperture fast optics Three mirrors, 8.4
m primary f1.25 optics
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LSST DOE groups SLAC, LLNL, BNL, UIUC, Harvard
This will be a new telescope, designed for the
science.
60 cm diameter focal plane to image 8.6
deg2 2.8?109 pixels (smaller pixels than DES -
better resolution)
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LSST
The survey (Im ignoring lots of
features) 5-band survey 400 - 1000 nm (similar
to DES) Sky area covered 18,000 deg2 (40 of
sky, 3x DES) Limiting magnitude 26.7 AB mag
10s (2 mag deeper than DES, 5 deeper than
SDSS) Source density 60 galaxies/sq.arcmin
(3-4x DES)
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LSST
Why a large, fast camera is important.
Limiting magnitude 26.7 AB mag _at_ 10s 2 mag
deeper than DES, 5 deeper than SDSS
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LSST
What we get (Im ignoring lots of things) 3
billion galaxies (10x DES) 250,000 Sne /
year 14,000 with dense follow-up z ? 1 covers
the critical region for w w. Allows searches
for SN model systematics 60 galaxies/sq.arcmin (
3-4x DES)
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LSST
Science payoff (Im ignoring lots of
things) sw 0.02 sw 0.05 sWm
0.09 sWL 0.06
Weak lensing clusters
Supernovae (no priors)