3,585 research outputs found
Measuring the hydrostatic mass bias in galaxy clusters by combining Sunyaev-Zel'dovich and CMB lensing data
The cosmological parameters prefered by the cosmic microwave background (CMB)
primary anisotropies predict many more galaxy clusters than those that have
been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This tension has
attracted considerable attention since it could be evidence of physics beyond
the simplest CDM model. However, an accurate and robust calibration of
the mass-observable relation for clusters is necessary for the comparison,
which has been proven difficult to obtain so far. Here, we present new
contraints on the mass-pressure relation by combining tSZ and CMB lensing
measurements about optically-selected clusters. Consequently, our galaxy
cluster sample is independent from the data employed to derive cosmological
constrains. We estimate an average hydrostatic mass bias of , with no significant mass nor redshift evolution. This value greatly
reduces the tension between the predictions of CDM and the observed
abundance of tSZ clusters while being in agreement with recent estimations from
tSZ clustering. On the other hand, our value for is higher than the
predictions from hydro-dynamical simulations. This suggests the existence of
mechanisms driving large departures from hydrostatic equilibrium and that are
not included in state-of-the-art simulations, and/or unaccounted systematic
errors such as biases in the cluster catalogue due to the optical selection.Comment: 4 pages, 3 figure
Status of superpressure balloon technology in the United States
Superpressure mylar balloon technology in United States - applications, balloon size criteria, and possible improvement
Extending the halo mass resolution of -body simulations
We present a scheme to extend the halo mass resolution of N-body simulations
of the hierarchical clustering of dark matter. The method uses the density
field of the simulation to predict the number of sub-resolution dark matter
haloes expected in different regions. The technique requires as input the
abundance of haloes of a given mass and their average clustering, as expressed
through the linear and higher order bias factors. These quantities can be
computed analytically or, more accurately, derived from a higher resolution
simulation as done here. Our method can recover the abundance and clustering in
real- and redshift-space of haloes with mass below at to better than 10%. We demonstrate the
technique by applying it to an ensemble of 50 low resolution, large-volume
-body simulations to compute the correlation function and covariance matrix
of luminous red galaxies (LRGs). The limited resolution of the original
simulations results in them resolving just two thirds of the LRG population. We
extend the resolution of the simulations by a factor of 30 in halo mass in
order to recover all LRGs. With existing simulations it is possible to generate
a halo catalogue equivalent to that which would be obtained from a -body
simulation using more than 20 trillion particles; a direct simulation of this
size is likely to remain unachievable for many years. Using our method it is
now feasible to build the large numbers of high-resolution large volume mock
galaxy catalogues required to compute the covariance matrices necessary to
analyse upcoming galaxy surveys designed to probe dark energy.Comment: 11 pages, 7 Figure
A Robust State Feedback Adaptive Controller with Improved Transient Tracking Error Bounds for Plants with Unknown Varying Control Gain
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