Abstracts
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Alvarez, Marcelo -- Large Scale Structure of Reionization
I will discuss the large scale three-dimensional structure of reionization, with
a focus on its characteristic scales and topology on scales ranging from 1 Mpc to
several Gpc. I will then attempt to make the connection to the z=0 universe.
Auger, Matt -- Strong Lensing: A Neglected Tool for Cosmology?
I will present recent results from strong lensing that have helped to inform our
understanding of cosmology and galaxy evolution. I will also discuss some promising
future prospects for strong lensing from wide area surveys such as PanSTARRS, LSST,
and SNAP.
Barnard, Michael -- What can we learn from future dark energy
probes?
We evaluate the ability of future data sets to discriminate among different quintessence
dark energy models. This approach gives an alternative measure for assessing the
impact of future experiments, as compared with the large body of literature that
compares experiments in abstract parameter spaces and more recent work that evaluates
the constraining power of experiments on individual parameter spaces of specific
quintessence models. We use the Dark Energy Task Force (DETF) models of future data
sets, and compare the discriminative power of experiments designated by the DETF
as Stages 2, 3, and 4. Our work reveals a minimal increase in discriminating power
when comparing Stage 3 to Stage 2, but a very striking increase in discriminating
power when going to Stage 4. We also see evidence that even modest improvements
over DETF Stage 4 could result in even more dramatic discriminating power among
quintessence dark energy models. We develop and demonstrate the technique of using
the independently measured modes of the equation of state as a common parameter
space in which to compare the different quintessence models, and we argue that this
technique is a powerful one. We use the PNGB, Exponential, Albrecht-Skordis, and
Inverse Tracker (or Inverse Power Law) quintessence models for this work. One of
our main results is that the goal of discriminating among these models sets a concrete
measure on the capabilities of future dark energy experiments. Experiments have
to be somewhat better than DETF Stage 4 simulated experiments to fully meet this
goal.
Comerford, Julie -- A New Way of Identifying Galaxy Mergers:
Offset AGN in Galaxy Merger Remnants
One of the predictions of the hierarchical paradigm for structure formation is that
some galaxies should exhibit two supermassive black holes (SMBHs) near their centers
as the result of a recent merger. Motivated by the serendipitous discovery of a
dual AGN in the DEEP2 Galaxy Redshift Survey, we conduct a systematic search of
the data for further dual SMBHs. While theoretically predicted, such phenomena are
difficult to observe and adequate samples have only recently become available with
the advent of new deep spectroscopic surveys. In a galaxy spectrum, redshift offsets
between AGN-fueled [O III] emission lines and the galaxy's stellar component suggest
a luminous AGN moving with respect to the host galaxy, signaling that the galaxy
recently underwent a merger. This new way of identifying galaxy mergers sidesteps
many of the assumptions plaguing merger counts via close pairs of galaxies or galaxy
morphologies. Since SMBHs do not usually power AGN, we expect galaxies hosting a
single offset AGN to be more common than galaxies hosting two AGN. We identify 22
offset AGN and 2 dual AGN in DEEP2 early-type galaxies, placing a lower limit of
~ 1 merger/Gyr for early-type galaxies at 0.3 < z < 0.9.
de Putter, Roland -- To Bin or Not To Bin: Parametrizing
the Dark Energy Equation of State
I will discuss the advantages and disadvantages of three popular ways of parametrizing
the dark energy equation of state: principal component analysis, uncorrelated bandpowers,
and the equation of state within redshift bins. I will argue that no one technique
is a panacea. An example of an issue that arises is that no parametrization has
both a clear physical interpretation and uncorrelated errors. Another example is
that the form of principal components is not unique and depends on the choice of
coordinate (i.e. redshift, scale factor, etc.). Specific lessons include the critical
role of proper treatment of the high redshift expansion history and the lack of
a unique, well defined signal-to-noise or figure of merit.
Gilmore, Rudy -- The Extragalactic Background Light and
Absorption in Gamma Ray Spectra
Recent state-of-the-art semi-analytic models (SAMs) can now accurately model the
history of galaxy formation and evolution. These SAMs utilize a 'forward evolution'
approach and include all of the important processes for determining photon emission
from galaxies, such as cooling and shock heating of gas, galaxy mergers, star formation
and aging, supernova and AGN feedback, and the reprocessing of light by dust. I
will be presenting our group's latest prediction of the extra-galactic background
light based on this work and will discuss the implications for the attenuation of
VHE gamma rays from distant sources due to pair-production. These results will be
compared to recent limits placed on the EBL by observations of GeV and TeV blazar
spectra by experiments such as H.E.S.S., MAGIC and VERITAS. The implications for
reconstructing the intrinsic spectra of distant blazars will be addressed.
Griffith, Roger -- Galaxy Morphologies In The Extended
Groth Strip from 0.2 < z < 1.2
Using multi-wavelength (V and I band) high resolution imaging obtained with the
Advanced Camera for Surveys on the \emph{Hubble Space Telescope} (HST) by the All
Wavelength Extended Groth Strip International Survey we measure morphological properties
for $\sim$ 55,000 objects in both V and I bands. The HST color images allow us to
investigate the morphological properties of the galaxies in two filters, thus allowing
us to compare and contrast the systematic differences in the measurements between
the two color bands. We present the results from a parametric technique (G\textsc{alfit}),
that measures the S$\acute{e}$rsic index $n$ and the half-light radius $r_e$ using
the S$\acute{e}$rsic profile. Our final morphology catalog consists of $\sim$ 11,000
galaxies with DEEP2 redshifts (spectroscopic and photometric) which have been visually
inspected for morphological accuracy. It has been shown that galaxy colors are bimodal
to $z\sim1$, which allows us to define two distinct galaxy populations, the red
sequence and the blue cloud. We are able to study the morphological properties of
these two distinct populations independently. We find a strong correlation between
galaxy colors and their morphologies, with $\sim$ 83 \% of the galaxies in the red
sequence having early-type morphologies $(n > 2.5)$ and $\sim$ 84 \% of the galaxies
in the blue cloud having late-type morphologies $(n < 1.5)$. We will use this catalog
to study morphological parameters for galaxies that span $0.2 < z < 1.2$.
Jee, James -- Dark Matter in the Galaxy Cluster CL1226+3332
at z=0.89
We present a weak-lensing analysis of the high-redshift galaxy cluster CL1226 at
z=0.89 based on HST/ACS data. On a large scale, the dark matter distribution is
symmetric with no significant substructure out to the virial radius, consistent
with the previous X-ray analysis results. The overall shear profile of the cluster
is well-described by an NFW model. However, on a small scale, the cluster center
is resolved into two mass clumps, following the cluster galaxy distribution. Combined
with the X-ray temperature map, the result supports the claim that the two groups
are merging.
Jeltema, Tesla -- The Hot Gas Halos of Galaxies in Groups
We use Chandra observations of 13 nearby groups of galaxies to investigate the hot
gas content of their member galaxies. We find that a large fraction of near-IR bright,
early-type galaxies in groups have extended X-ray emission, indicating that they
retain significant hot gas halos even in these dense environments. In particular,
we detect hot gas halos in ~80% of L_K > L_star galaxies. We do not find a significant
difference in the L_K-L_X relation for detected group and cluster early-type galaxies.
However, we detect X-ray emission from a significantly higher fraction of galaxies
brighter than L_star in groups compared to clusters, indicating that a larger fraction
of galaxies in clusters experience significant stripping of their hot gas. In addition,
group and cluster galaxies appear to be X-ray faint compared to field galaxies,
though a Chandra based field sample is needed to confirm this result. The near-IR
bright late-types galaxies in clusters and groups appear to follow the L_K-L_X relation
for early-type galaxies, while near-IR fainter late-type galaxies are significantly
more X-ray luminous than this relation likely due to star formation. Finally, we
find individual examples of ongoing gas stripping of group galaxies. One galaxy
shows a 40-50 kpc X-ray tail, and two merging galaxy systems show tidal bridges/tails
of X-ray emission. Therefore, stripping of hot galactic gas through both ram pressure
and tidal forces does occur in groups and clusters, but the frequency or efficiency
of such events must be moderate enough to allow hot gas halos in a large fraction
of bright galaxies to survive even in group and cluster cores.
Jeong, Eunhwa -- Probing Non-Gaussianity In WMAP 5-year DATA:
One Point Distribution Function
We analyze WMAP 5-year data using the one-point distribution functions to probe
the non-Gaussianity in the CMB Anisotropy data. Our work provides an independent
test on non-Gaussianity besides Bispectrum and Minkowski Functionals. Computer simulations
are performed to determine the uncertainties of the results.
Kirby, Evan -- Discovery of Extremely Metal-Poor Stars in
the Ultra-Faint Dwarf Spheroidal Galaxies
We present metallicity distribution functions (MDFs) for the faintest dwarf spheroidal
galaxies (dSphs) in the Milky Way (MW) system. The MDFs for the dSphs resemble the
MDF for the metal-poor component of the MW halo, except that the dSphs are shifted
more metal-poor by 0.4 dex. Additionally, we present the first spectroscopic metallicities
at [Fe/H] < -3.0 of stars outside of the MW halo. This discovery supports the Searle-Zinn
galaxy assembly paradigm wherein dSphs dissolve to form the stellar halo. These
[Fe/H] measurements are possible through medium resolution spectroscopy coupled
with spectral synthesis. This technique is not tied to empirical metallicity calibrations
and is therefore able to probe extremely metal-poor regimes.
Leaman, Jesse -- Supernova Rates in the Local Universe
Applying the control time method to the Lick Observatory Supernova Search database
we have determined the most accurate supernova rate to date, in the nearby (z<0.05)
universe. Using more than 600 Supernovae, rates of various supernova types (Ia,
Ib/c, II) have been calculated as a function of host galaxy morphology, B-K color,
and radio loudness. Then we determine the rates per unit volume, considering the
whole galaxy sample, and compare the results with other volumetric supernova rate
studies at higher redshifts. Potential cosmological implications are discussed.
Lueker, Martin -- The SPT Sunyaev-Zeldovich Survey
After a very successful receiver upgrade this summer, the South Pole Telescope (SPT)
has resumed its search for high-redshift galaxy clusters using the Sunyaev-Zeldovich
Effect (SZE). In this talk, I will describe the science goals of the SPT SZE survey.
I will also give an update on the status of the instrument and our observing plans.
Perl, Martin -- Can Dark Energy Be Directly Detected?
I discuss proposals for directly detecting dark energy with laboratory experiments.
All of these proposals seem to have flaws. However dark energy density is much larger
than the the detectable energy density of very small electric fields. Is direct
detection of dark energy impossible?
Plagge, Tom -- APEX-SZ: Project Status
APEX-SZ is a millimeter-wavelength bolometric instrument on the 12-meter Atacama
Pathfinder EXperiment telescope, designed to map the Cosmic Microwave Background
(CMB) to 10s of $\mu K_{CMB}$ sensitivity per arcminute pixel over a large patch
of sky. In addition to probing the CMB power spectrum at small angular scales, APEX-SZ
will discover and catalog clusters of galaxies via their Sunyaev-Zel'dovich Effect
signature in the CMB. These cluster observations will serve to constrain cosmological
parameters and to test theories of structure formation. I will briefly review the
Sunyaev-Zel'dovich Effect, describe the APEX-SZ instrument, and discuss the current
status of the project.
Profumo, Stefano -- Non-thermal X-rays from galaxy clusters
and dark matter annihilation
dark matter annihilation We investigate a scenario where the recently discovered
non-thermal hard X-ray emission from the Ophiuchus cluster originates from inverse
Compton scattering of energetic electrons and positrons produced in weakly interacting
dark matter pair annihilations. We show that this scenario can account for both
the X-ray and the radio emission, provided the average magnetic field is of the
order of 0.1 microGauss. We demonstrate that GLAST will conclusively test the dark
matter annihilation hypothesis. Depending on the particle dark matter model, GLAST
might even detect the monochromatic line produced by dark matter pair annihilation
into two photons.
Reichardt, Christian -- Recent Results from ACBAR
The Arcminute Cosmology Bolometer Array Receiver (ACBAR) is a multi-frequency 16-element
bolometer array which observed from the 2m Viper telescope at the South Pole during
the 2001, 2002, 2004 and 2005 Austral winters. ACBAR's small (5') beams allow it
to probe the damping tail of the cosmic microwave background (CMB) power spectrum,
making it highly complementary to experiments at larger angular scales such as WMAP
and Boomerang. I will present recent results from the complete set of ACBAR's CMB
temperature anisotropy observations. We include new data from the final 2005 observing
season, expanding the number of detector-hours by 210% and the sky coverage by 490%
over the data set used in the previous ACBAR release. As a result, the band-power
uncertainties have been reduced by more than a factor of two on angular scales encompassing
the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum.
The calibration uncertainty has been reduced from 6% to 2.2% in temperature through
a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated
WMAP3 experiment. The measured power spectrum is consistent with a spatially flat,
LambdaCDM cosmological model. We see evidence for weak gravitational lensing of
the CMB by comparing the likelihood for the best-fit lensed/unlensed models to the
ACBAR+WMAP3 data. On fine angular scales, there is weak evidence (1.7 sigma) for
excess power above the level expected from primary anisotropies. The source of this
power cannot be constrained by the ACBAR 150 GHz observations alone; however, if
it is the same signal seen at 30 GHz by the CBI and BIMA experiments, then it has
a spectrum consistent with the Sunyaev-Zel'dovich effect.
Rubin, David -- Cosmological Constraints from the Union Supernova
Compilation
We present the results of an analysis of the world SNe data, complemented by a new
dataset of low-redshift nearby-Hubble-flow SN Ia. This "Union" compilation of nearly
400 SN Ia includes the recent large samples of SNe Ia from the Supernova Legacy
Survey and the ESSENCE Survey, the older datasets, as well as the recently extended
dataset of distant supernovae observed with HST. A single, consistent and blind
analysis procedure is used for all the various SN Ia subsamples. We present the
latest results from this Union compilation and its combination with other cosmological
measurements (CMB and BAO), and discuss the cosmological constraints on the dark
energy density. With the addition of our new nearby Hubble-flow SNe Ia, these resulting
cosmological constraints are currently the tightest available. While our results
are consistent with a cosmological constant, we obtain only relatively weak constraints
on an equation of state, w, that varies with redshift. In particular, the current
data do not yet significantly constrain w at z > 1.
Spolyar, Douglas -- The effect of dark matter on the first
stars: a new phase of stellar evolution
Nobel Laureate David Gross recently commented that LHC is being built for Super
Symmetry, Super Symmetry, Super Symmetry! The Lightest Super Symmetric Partner (LSP)
is arguably the most favored dark matter candidate. In this talk, two mechanism
are identified whereby dark matter (DM) in proto stellar halos can dramatically
alter the formation of the first stars, which may lead to a new phase of stellar
evolution driven by DM annihilation and the LSP in particular.
Venkatesan, Aparna -- Microwave Background constraints
on the efficiency of high-redshift star formation
I review the constraints provided by the cosmic microwave background (CMB) on the
epoch of reionization of the intergalactic medium (IGM), and on the astrophysics
of the reionizing sources. I will then present the limits set by the recent WMAP-5
CMB optical depth data on the efficiency of high-redshift star formation. Over half
of this optical depth can be accounted for by a fully ionized IGM back to redshifts
of about 7, when including the ionization of helium. At higher redshifts, a partially
ionized IGM resulting from early massive stars and black holes can be used to constrain
the ionizing contributions of “first light” sources.
von der Linden, Anja -- From Blue to Red (via Green?) - Galaxy
Population Gradients in Galaxy Clusters
Using a sample of 500 local galaxy clusters from SDSS, I investigate the star formation
history of the galaxy population as function of distance from the cluster center
and of galaxy stellar mass. Since distance from the cluster center anti-correlates
with the time since cluster infall, it can serve as a probe for the timescales involved
in shutting down star formation in cluster galaxies. The observed population gradients
are best matched by comparatively slow timescales of the order of a few Gyrs. Furthermore,
the characteristic mass of cluster galaxies does not change as function of clustercentric
radius, suggesting that the involved processes are largely non-disruptive. Together,
these results yield strangulation (i.e. stripping of the hot gas envelope upon cluster
infall) a viable dominant mechanism to quench star formation in cluster galaxies.
Wetzel, Andrew -- Galaxy Merger Counts & Clustering at z~2.5
Using high-resolution N-body simulations, I will discuss the statistical properties
of galaxy (subhalo) mergers at high redshifts, including merger counts and evolution
with redshift, clustering, and relation to host dark matter halos.
Wu, Hao-Yi -- Self Calibration: Systematics and Efficacy
I will talk about the self-calibration technique in galaxy cluster surveys (Lima
& Hu 04), focusing on one of the potential systematics: the halo assembly bias (Wu
et al. 08, arXiv:0803.1491). I will then discuss the efficacy of self calibration
when various uncertainties in observable—mass relations are presented, and the possibility
of constructing realistic observable—mass relations for DES.
Zemp, Marcel -- Via Lactea II: Clumps and streams in the dark
matter distribution
Via Lactea II simulates the assembly of a Milky Way size cold dark matter halo within
a LCDM universe. In total, there are over 10^9 particles in the simulation and the
final virialized region is resolved by approximately 5 x 10^8 particles. This high
resolution allows us for the first time to resolve local (i.e. at 8 kpc) substructure.
We find hundreds of very concentrated dark matter clumps surviving near the solar
system, as well as numerous cold streams. For the first time we also find substructure
within substructure.