561 research outputs found
Background Subtraction Uncertainty from Submillimetre to Millimetre Wavelengths
Photometric observations of galaxies at submillimetre to millimetre
wavelengths (50 - 1000 GHz) are susceptible to spatial variations in both the
background CMB temperature and CIB emission that can be comparable to the flux
from the target galaxy. We quantify the residual uncertainty when background
emission inside a circular aperture is estimated by the mean flux in a
surrounding annular region, assumed to have no contribution from the source of
interest. We present simple formulae to calculate this uncertainty as a
function of wavelength and aperture size. Drawing on examples from the
literature, we illustrate the use of our formalism in practice and highlight
cases in which uncertainty in the background subtraction needs to be considered
in the error analysis. We make the code used to calculate the uncertainties
publicly available on the web.Comment: 7 pages, 5 figures, comments welcom
Weak Lensing of Intensity Mapping: the Cosmic Infrared Background
Gravitational lensing deflects the paths of cosmic infrared background (CIB)
photons, leaving a measurable imprint on CIB maps. The resulting statistical
anisotropy can be used to reconstruct the matter distribution out to the
redshifts of CIB sources. To this end, we generalize the CMB lensing quadratic
estimator to any weakly non-Gaussian source field, by deriving the optimal
lensing weights. We point out the additional noise and bias caused by the
non-Gaussianity and the `self-lensing' of the source field. We propose methods
to reduce, subtract or model these non-Gaussianities. We show that CIB lensing
should be detectable with Planck data, and detectable at high significance for
future CMB experiments like CCAT-Prime. The CIB thus constitutes a new source
image for lensing studies, providing constraints on the amplitude of structure
at intermediate redshifts between galaxies and the CMB. CIB lensing
measurements will also give valuable information on the star formation history
in the universe, constraining CIB halo models beyond the CIB power spectrum. By
laying out a detailed treatment of lens reconstruction from a weakly
non-Gaussian source field, this work constitutes a stepping stone towards lens
reconstruction from continuum or line intensity mapping data, such as the
Lyman-alpha emission, absorption, and the 21cm radiation.Comment: Accepted in Physical Review
Reconstructing Small Scale Lenses from the Cosmic Microwave Background Temperature Fluctuations
Cosmic Microwave Background (CMB) lensing is a powerful probe of the matter
distribution in the Universe. The standard quadratic estimator, which is
typically used to measure the lensing signal, is known to be suboptimal for
low-noise polarization data from next-generation experiments. In this paper we
explain why the quadratic estimator will also be suboptimal for measuring
lensing on very small scales, even for measurements in temperature where this
estimator typically performs well. Though maximum likelihood methods could be
implemented to improve performance, we explore a much simpler solution,
revisiting a previously proposed method to measure lensing which involves a
direct inversion of the background gradient. An important application of this
simple formalism is the measurement of cluster masses with CMB lensing. We find
that directly applying a gradient inversion matched filter to simulated lensed
images of the CMB can tighten constraints on cluster masses compared to the
quadratic estimator. While the difference is not relevant for existing surveys,
for future surveys it can translate to significant improvements in mass
calibration for distant clusters, where galaxy lensing calibration is
ineffective due to the lack of enough resolved background galaxies.
Improvements can be as large as for a cluster at and a
next-generation CMB experiment with 1K-arcmin noise, and over an order of
magnitude for lower noise levels. For future surveys, this simple
matched-filter or gradient inversion method approaches the performance of
maximum likelihood methods, at a fraction of the computational cost.Comment: 11 pages, 7 figure
Supersonic baryon-CDM velocities and CMB B-mode polarization
It has recently been shown that supersonic relative velocities between dark
matter and baryonic matter can have a significant effect on formation of the
first structures in the universe. If this effect is still non-negligible during
the epoch of hydrogen reionization, it generates large-scale anisotropy in the
free electron density, which gives rise to a CMB B-mode. We compute the B-mode
power spectrum and find a characteristic shape with acoustic peaks at l ~ 200,
400, ... The amplitude of this signal is a free parameter which is related to
the dependence of the ionization fraction on the relative baryon-CDM velocity
during the epoch of reionization. However, we find that the B-mode signal is
undetectably small for currently favored reionization models in which hydrogen
is reionized promptly at z ~ 10, although constraints on this signal by future
experiments may help constrain models in which partial reionization occurs at
higher redshift, e.g. by accretion onto primordial black holes.Comment: 5 pages, 3 figure
Future constraints on halo thermodynamics from combined Sunyaev-Zel'dovich measurements
The improving sensitivity of measurements of the kinetic Sunyaev-Zel'dovich
(SZ) effect opens a new window into the thermodynamic properties of the baryons
in halos. We propose a methodology to constrain these thermodynamic properties
by combining the kinetic SZ, which is an unbiased probe of the free electron
density, and the thermal SZ, which probes their thermal pressure. We forecast
that our method constrains the average thermodynamic processes that govern the
energetics of galaxy evolution like energetic feedback across all redshift
ranges where viable halos sample are available. Current Stage-3 cosmic
microwave background (CMB) experiments like AdvACT and SPT-3G can measure the
kSZ and tSZ to greater than 100 if combined with a DESI-like
spectroscopic survey. Such measurements translate into percent-level
constraints on the baryonic density and pressure profiles and on the feedback
and non-thermal pressure support parameters for a given ICM model. This in turn
will provide critical thermodynamic tests for sub-grid models of feedback in
cosmological simulations of galaxy formation. The high fidelity measurements
promised by the next generation CMB experiment, CMB-S4, allow one to further
sub-divide these constraints beyond redshift into other classifications, like
stellar mass or galaxy type.Comment: 11 pages, 3 figures, Accepted to JCA
Cluster Abundance in f(R) Gravity Models
As one of the most powerful probes of cosmological structure formation, the
abundance of massive galaxy clusters is a sensitive probe of modifications to
gravity on cosmological scales. In this paper, we present results from N-body
simulations of a general class of f(R) models, which self-consistently solve
the non-linear field equation for the enhanced forces. Within this class we
vary the amplitude of the field, which controls the range of the enhanced
gravitational forces, both at the present epoch and as a function of redshift.
Most models in the literature can be mapped onto the parameter space of this
class. Focusing on the abundance of massive dark matter halos, we compare the
simulation results to a simple spherical collapse model. Current constraints
lie in the large-field regime, where the chameleon mechanism is not important.
In this regime, the spherical collapse model works equally well for a wide
range of models and can serve as a model-independent tool for placing
constraints on f(R) gravity from cluster abundance. Using these results, we
show how constraints from the observed local abundance of X-ray clusters on a
specific f(R) model can be mapped onto other members of this general class of
models.Comment: 8 pages, 6 figure
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