4,130 research outputs found
The Impact of Halo Properties, Energy Feedback and Projection Effects on the Mass-SZ Flux Relation
We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}.Comment: 12 pages, 6 figures, to be submitted to Ap
CMB Lensing Power Spectrum Biases from Galaxies and Clusters using High-angular Resolution Temperature Maps
The lensing power spectrum from cosmic microwave background (CMB) temperature
maps will be measured with unprecedented precision with upcoming experiments,
including upgrades to ACT and SPT. Achieving significant improvements in
cosmological parameter constraints, such as percent level errors on sigma_8 and
an uncertainty on the total neutrino mass of approximately 50 meV, requires
percent level measurements of the CMB lensing power. This necessitates tight
control of systematic biases. We study several types of biases to the
temperature-based lensing reconstruction signal from foreground sources such as
radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from
galaxy clusters. These foregrounds bias the CMB lensing signal due to their
non-Gaussian nature. Using simulations as well as some analytical models we
find that these sources can substantially impact the measured signal if left
untreated. However, these biases can be brought to the percent level if one
masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with
masses above M_vir = 10^14 M_sun. To achieve such percent level bias, we find
that only modes up to a maximum multipole of l_max ~ 2500 should be included in
the lensing reconstruction. We also discuss ways to minimize additional bias
induced by such aggressive foreground masking by, for example, exploring a
two-step masking and in-painting algorithm.Comment: 14 pages, 14 figures, to be submitted to Ap
External Shear in Quadruply Imaged Lens Systems
We use publicly available N-body simulations and semi-analytic models of
galaxy formation to estimate the levels of external shear due to structure near
the lens in gravitational lens systems. We also describe two selection effects,
specific to four-image systems, that enhance the probability of observing
systems to have higher external shear. Ignoring additional contributions from
"cosmic shear" and assuming that lens galaxies are not significantly flattened,
we find that the mean shear at the position of a quadruple lens galaxy is 0.11,
the rms shear is roughly 0.15, and there is roughly a 45% likelihood of
external shear greater than 0.1. This is much larger than previous estimates
and in good agreement with typical measured external shear. The higher shear
primarily stems from the tendency of early-type galaxies, which are the
majority of lenses, to reside in overdense regions.Comment: 5 pages, 2 figures, ApJ in press, minor revision
Non-Gaussian Scatter in Cluster Scaling Relations
We investigate the impact of non-Gaussian scatter in the cluster
mass-observable scaling relation on the mass and redshift distribution of
clusters detected by wide area surveys. We parameterize non-Gaussian scatter by
incorporating the third and forth moments (skewness and kurtosis) into the
distribution P(Mobs|M). We demonstrate that for low scatter mass proxies the
higher order moments do not significantly affect the observed cluster mass and
redshift distributions. However, for high scatter mass indicators it is
necessary for the survey limiting mass threshold to be less than 10^14 h^-1
Msol to prevent the skewness from having a significant impact on the observed
number counts, particularly at high redshift. We also show that an unknown
level of non-Gaussianity in the scatter is equivalent to an additional
uncertainty on the variance in P(Mobs|M) and thus may limit the constraints
that can be placed on the dark energy equation of state parameter w.
Furthermore, positive skewness flattens the mass function at the high mass end,
and so one must also account for skewness in P(Mobs|M) when using the shape of
the mass function to constrain cluster scaling-relations.Comment: 6 Pages, 3 Figures, to be submitted to ApJ Letter
Theory of Dynamic Stripe Induced Superconductivity
Since the recently reported giant isotope effect on T* [1] could be
consistently explained within an anharmonic spin-charge-phonon interaction
model, we consider here the role played by stripe formation on the
superconducting properties within the same model. This is a two-component
scenario and we recast its basic elements into a BCS effective Hamiltonian. We
find that the stripe formation is vital to high-Tc superconductivity since it
provides the glue between the two components to enhance Tc to the unexpectedly
large values observed experimentally.Comment: 7 pages, 2 figure
Constraints on Cosmological Parameters from Future Galaxy Cluster Surveys
We study the expected redshift evolution of galaxy cluster abundance between
0 < z < 3 in different cosmologies, including the effects of the cosmic
equation of state parameter w=p/rho. Using the halo mass function obtained in
recent large scale numerical simulations, we model the expected cluster yields
in a 12 deg^2 Sunyaev-Zeldovich Effect (SZE) survey and a deep 10^4 deg^2 X-ray
survey over a wide range of cosmological parameters. We quantify the
statistical differences among cosmologies using both the total number and
redshift distribution of clusters. Provided that the local cluster abundance is
known to a few percent accuracy, we find only mild degeneracies between w and
either Omega_m or h. As a result, both surveys will provide improved
constraints on Omega_m and w. The Omega_m-w degeneracy from both surveys is
complementary to those found either in studies of CMB anisotropies or of
high-redshift Supernovae (SNe). As a result, combining these surveys together
with either CMB or SNe studies can reduce the statistical uncertainty on both w
and Omega_m to levels below what could be obtained by combining only the latter
two data sets. Our results indicate a formal statistical uncertainty of about
3% (68% confidence) on both Omega_m and w when the SZE survey is combined with
either the CMB or SN data; the large number of clusters in the X-ray survey
further suppresses the degeneracy between w and both Omega_m and h. Systematics
and internal evolution of cluster structure at the present pose uncertainties
above these levels. We briefly discuss and quantify the relevant systematic
errors. By focusing on clusters with measured temperatures in the X-ray survey,
we reduce our sensitivity to systematics such as non-standard evolution of
internal cluster structure.Comment: ApJ, revised version. Expanded discussion of systematics;
Press-Schechter mass function replaced by fit from simulation
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