80 research outputs found
Dark Energy Constraints from Galaxy Cluster Peculiar Velocities
Future multifrequency microwave background experiments with arcminute
resolution and micro-Kelvin temperature sensitivity will be able to detect the
kinetic Sunyaev-Zeldovich (kSZ) effect, providing a way to measure radial
peculiar velocities of massive galaxy clusters. We show that cluster peculiar
velocities have the potential to constrain several dark energy parameters. We
compare three velocity statistics (the distribution of radial velocities, the
mean pairwise streaming velocity, and the velocity correlation function) and
analyze the relative merits of these statistics in constraining dark energy
parameters. Of the three statistics, mean pairwise streaming velocity provides
constraints that are least sensitive to velocity errors: the constraints on
parameters degrades only by a factor of two when the random error is increased
from 100 to 500 km/s. We also compare cluster velocities with other dark energy
probes proposed in the Dark Energy Task Force report. For cluster velocity
measurements with realistic priors, the eventual constraints on the dark energy
density, the dark energy equation of state and its evolution are comparable to
constraints from supernovae measurements, and better than cluster counts and
baryon acoustic oscillations; adding velocity to other dark energy probes
improves constraints on the figure of merit by more than a factor of two. For
upcoming Sunyaev-Zeldovich galaxy cluster surveys, even velocity measurements
with errors as large as 1000 km/s will substantially improve the cosmological
constraints compared to using the cluster number density alone.Comment: 25 pages, 10 figures. Results and conclusions unchanged. Minor
changes to match the accepted version in Physical Review
Impact of Systematic Errors in Sunyaev-Zel'dovich Surveys of Galaxy Clusters
Future high-resolution microwave background measurements hold the promise of
detecting galaxy clusters throughout our Hubble volume through their
Sunyaev-Zel'dovich (SZ) signature, down to a given limiting flux. The number
density of galaxy clusters is highly sensitive to cluster mass through
fluctuations in the matter power spectrum, as well as redshift through the
comoving volume and the growth factor. This sensitivity in principle allows
tight constraints on such quantities as the equation of state of dark energy
and the neutrino mass. We evaluate the ability of future cluster surveys to
measure these quantities simultaneously when combined with PLANCK-like CMB
data. Using a simple effective model for uncertainties in the cluster mass-SZ
flux relation, we evaluate systematic shifts in cosmological constraints from
cluster SZ surveys. We find that a systematic bias of 10% in cluster mass
measurements can give rise to shifts in cosmological parameter estimates at
levels larger than the statistical errors. Systematic errors are
unlikely to be detected from the mass and redshift dependence of cluster number
counts alone; increasing survey size has only a marginal effect. Implications
for upcoming experiments are discussed.Comment: 12 pages, 6 figures; accepted to JCAP; revised to match submitted
versio
Milgrom Relation Models for Spiral Galaxies from Two-Dimensional Velocity Maps
Using two-dimensional velocity maps and I-band photometry, we have created
mass models of 40 spiral galaxies using the Milgrom relation (the basis of
modified Newtonian dynamics, or MOND) to complement previous work. A Bayesian
technique is employed to compare several different dark matter halo models to
Milgrom and Newtonian models. Pseudo-isothermal dark matter halos provide the
best statistical fits to the data in a majority of cases, while the Milgrom
relation generally provides good fits as well. We also find that Milgrom models
give mass-to-light ratios that roughly correlate with galaxy color, as
predicted by stellar population models. A subsample of galaxies in the Hydra
cluster follow a tight relation between mass-to-light and color, but one that
is significantly different from relations found in previous studies. Ruling out
the Milgrom relation with rotational kinematics is difficult due to systematic
uncertainties in the observations as well as underlying model assumptions. We
discuss in detail two galaxies for which the Milgrom relation appears to fail
and find that relaxing the assumption of constant stellar mass-to-light ratio
can maintain Milgrom models' viability.Comment: accepted for publication in The Astronomical Journal; 17 page
Cosmic topology. Part II. Eigenmodes, correlation matrices, and detectability of orientable Euclidean manifolds
If the Universe has non-trivial spatial topology, observables depend on both
the parameters of the spatial manifold and the position and orientation of the
observer. In infinite Euclidean space, most cosmological observables arise from
the amplitudes of Fourier modes of primordial scalar curvature perturbations.
Topological boundary conditions replace the full set of Fourier modes with
specific linear combinations of selected Fourier modes as the eigenmodes of the
scalar Laplacian. We present formulas for eigenmodes in orientable Euclidean
manifolds with the topologies - , , , , and
that encompass the full range of manifold parameters and observer
positions, generalizing previous treatments. Under the assumption that the
amplitudes of primordial scalar curvature eigenmodes are independent random
variables, for each topology we obtain the correlation matrices of Fourier-mode
amplitudes (of scalar fields linearly related to the scalar curvature) and the
correlation matrices of spherical-harmonic coefficients of such fields sampled
on a sphere, such as the temperature of the cosmic microwave background (CMB).
We evaluate the detectability of these correlations given the cosmic variance
of the observed CMB sky. We find that topologies where the distance to our
nearest clone is less than about 1.2 times the diameter of the last scattering
surface of the CMB give a correlation signal that is larger than cosmic
variance noise in the CMB. This implies that if cosmic topology is the
explanation of large-angle anomalies in the CMB, then the distance to our
nearest clone is not much larger than the diameter of the last scattering
surface. We argue that the topological information is likely to be better
preserved in three-dimensional data, such as will eventually be available from
large-scale structure surveys.Comment: 79 pages, 9 figure
Systematic Errors in Sunyaev-Zeldovich Surveys of Galaxy Cluster Velocities
Galaxy cluster surveys compiled via the Sunyaev-Zeldovich Effect have the
potential to place strong constraints on cosmology, and in particular the
nature of dark energy. Here we consider cluster velocity surveys using kinetic
Sunyaev-Zeldovich measurements. Cluster velocities closely trace the
large-scale velocity field independent of cluster mass; we demonstrate that two
useful cluster velocity statistics are nearly independent of cluster mass, in
marked contrast to cluster number count statistics. On the other hand, cluster
velocity determinations from three-band observations of Sunyaev-Zeldovich
distortions can require additional cluster data or assumptions, and are
complicated by microwave emission from dusty galaxies and radio sources, which
may be correlated with clusters. Systematic errors in velocity due to these
factors can give substantial biases in determination of dark energy parameters,
although large cluster velocity surveys will contain enough information that
the errors can be modeled using the data itself, with little degradation in
cosmological constraints.Comment: 8 pages, 2 figures. Minor changes in the text to match the accepted
version. Conclusions unchange
Cosmological Parameters from Pre-Planck CMB Measurements
Recent data from the WMAP, ACT and SPT experiments provide precise
measurements of the cosmic microwave background temperature power spectrum over
a wide range of angular scales. The combination of these observations is well
fit by the standard, spatially flat LCDM cosmological model, constraining six
free parameters to within a few percent. The scalar spectral index, n_s =
0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with
simple models of inflation. The damping tail of the power spectrum at high
resolution, combined with the amplitude of gravitational lensing measured by
ACT and SPT, constrains the effective number of relativistic species to be
N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of
light neutrinos.Comment: 5 pages, 4 figure
Gravitational Radiation From Cosmological Turbulence
An injection of energy into the early Universe on a given characteristic
length scale will result in turbulent motions of the primordial plasma. We
calculate the stochastic background of gravitational radiation arising from a
period of cosmological turbulence, using a simple model of isotropic
Kolmogoroff turbulence produced in a cosmological phase transition. We also
derive the gravitational radiation generated by magnetic fields arising from a
dynamo operating during the period of turbulence. The resulting gravitational
radiation background has a maximum amplitude comparable to the radiation
background from the collision of bubbles in a first-order phase transition, but
at a lower frequency, while the radiation from the induced magnetic fields is
always subdominant to that from the turbulence itself. We briefly discuss the
detectability of such a signal.Comment: 20 pages. Corrections for an errant factor of 2 in all the gravity
wave characteristic amplitudes. Accepted for publication in Phys. Rev.
The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature Distribution
We present a detection of the unnormalized skewness induced by the
thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope
(ACT) 148 GHz cosmic microwave background temperature maps. Contamination due
to infrared and radio sources is minimized by template subtraction of resolved
sources and by constructing a mask using outlying values in the 218 GHz
(tSZ-null) ACT maps. We measure = -31 +- 6 \mu K^3 (measurement error
only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT
data, a 5-sigma detection. We show that the skewness is a sensitive probe of
sigma_8, and use analytic calculations and tSZ simulations to obtain
cosmological constraints from this measurement. From this signal alone we infer
a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our
results demonstrate that measurements of non-Gaussianity can be a useful method
for characterizing the tSZ effect and extracting the underlying cosmological
information.Comment: 9 pages, 5 figures. Replaced with version accepted by Phys. Rev. D,
with improvements to the likelihood function and the IR source treatment;
only minor changes in the result
Cosmological parameters from pre-Planck CMB measurements: a 2017 update
We present cosmological constraints from the combination of the full mission nine-year WMAP release and small-scale temperature data from the pre-Planck Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) generation of instruments. This is an update of the analysis presented in Calabrese et al. [Phys. Rev. D 87, 103012 (2013)], and highlights the impact on ΛCDM cosmology of a 0.06 eV massive neutrino—which was assumed in the Planck analysis but not in the ACT/SPT analyses—and a Planck-cleaned measurement of the optical depth to reionization. We show that cosmological constraints are now strong enough that small differences in assumptions about reionization and neutrino mass give systematic differences which are clearly detectable in the data. We recommend that these updated results be used when comparing cosmological constraints from WMAP, ACT and SPT with other surveys or with current and future full-mission Planck cosmology. Cosmological parameter chains are publicly available on the NASA’s LAMBDA data archive
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.).Comment: 32 pages, 21 figures To appear in J. Cosmology and Astroparticle
Physic
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