31 research outputs found
Bayesian analysis of an anisotropic universe model: systematics and polarization
We revisit the anisotropic universe model previously developed by Ackerman,
Carroll and Wise (ACW), and generalize both the theoretical and computational
framework to include polarization and various forms of systematic effects. We
apply our new tools to simulated WMAP data in order to understand the potential
impact of asymmetric beams, noise mis-estimation and potential Zodiacal light
emission. We find that neither has any significant impact on the results. We
next show that the previously reported ACW signal is also present in the 1-year
WMAP temperature sky map presented by Liu & Li, where data cuts are more
aggressive. Finally, we reanalyze the 5-year WMAP data taking into account a
previously neglected (-i)^{l-l'}-term in the signal covariance matrix. We still
find a strong detection of a preferred direction in the temperature map.
Including multipoles up to l=400, the anisotropy amplitude for the W-band is
found to be g = 0.29 +- 0.031, nonzero at 9 sigma. However, the corresponding
preferred direction is also shifted very close to the ecliptic poles at (l,b)=
(96,30), in agreement with the analysis of Hanson & Lewis, indicating that the
signal is aligned along the plane of the solar system. This strongly suggests
that the signal is not of cosmological origin, but most likely is a product of
an unknown systematic effect. Determining the nature of the systematic effect
is of vital importance, as it might affect other cosmological conclusions from
the WMAP experiment. Finally, we provide a forecast for the Planck experiment
including polarization.Comment: 9 pages, 8 figure
Lorentz Violation in Goldstone Gravity
We consider a theory of gravity in which a symmetric two-index tensor in
Minkowski spacetime acquires a vacuum expectation value (vev) via a potential,
thereby breaking Lorentz invariance spontaneously. When the vev breaks all the
generators of the Lorentz group, six Goldstone modes emerge, two linear
combinations of which have properties that are identical to those of the
graviton in general relativity. Integrating out massive modes yields an
infinite number of Lorentz-violating radiative-correction terms in the
low-energy effective Lagrangian. We examine a representative subset of these
terms and show that they modify the dispersion relation of the two propagating
graviton modes such that their phase velocity is direction-dependent. If the
phase velocity of the Goldstone gravitons is subluminal, cosmic rays can emit
gravi-Cherenkov radiation, and the detection of high-energy cosmic rays can be
used to constrain these radiative correction terms. Test particles in the
vicinity of the Goldstone gravitons undergo longitudinal oscillations in
addition to the usual transverse oscillations as predicted by general
relativity. Finally, we discuss the possibility of having vevs that do not
break all six generators and examine in detail one such theory.Comment: 14 page
Foreground Separation and Constraints on Primordial Gravitational Waves with the PICO Space Mission
PICO is a concept for a NASA probe-scale mission aiming to detect or
constrain the tensor to scalar ratio , a parameter that quantifies the
amplitude of inflationary gravity waves. We carry out map-based component
separation on simulations with five foreground models and input values
and . We forecast determinations using a
Gaussian likelihood assuming either no delensing or a residual lensing factor
= 27%. By implementing the first full-sky, post
component-separation, map-domain delensing, we show that PICO should be able to
achieve = 22% - 24%. For four of the five foreground models we
find that PICO would be able to set the constraints r < 1.3 \times 10^{-4}
\,\, \mbox{to} \,\, r <2.7 \times 10^{-4}\, (95\%) if , the
strongest constraints of any foreseeable instrument. For these models,
is recovered with confidence levels between and
. We find weaker, and in some cases significantly biased, upper
limits when removing few low or high frequency bands. The fifth model gives a
detection when and a bias with .
However, by correlating determinations from many small 2.5% sky areas with
the mission's 555 GHz data we identify and mitigate the bias. This analysis
underscores the importance of large sky coverage. We show that when only low
multipoles are used, the non-Gaussian shape of the true
likelihood gives uncertainties that are on average 30% larger than a Gaussian
approximation.Comment: 34 pages, 13 figures, published in JCA
COMAP Early Science: IV. Power Spectrum Methodology and Results
We present the power spectrum methodology used for the first-season COMAP
analysis, and assess the quality of the current data set. The main results are
derived through the Feed-feed Pseudo-Cross-Spectrum (FPXS) method, which is a
robust estimator with respect to both noise modeling errors and experimental
systematics. We use effective transfer functions to take into account the
effects of instrumental beam smoothing and various filter operations applied
during the low-level data processing. The power spectra estimated in this way
have allowed us to identify a systematic error associated with one of our two
scanning strategies, believed to be due to residual ground or atmospheric
contamination. We omit these data from our analysis and no longer use this
scanning technique for observations. We present the power spectra from our
first season of observing and demonstrate that the uncertainties are
integrating as expected for uncorrelated noise, with any residual systematics
suppressed to a level below the noise. Using the FPXS method, and combining
data on scales we estimate , the first direct 3D
constraint on the clustering component of the CO(1-0) power spectrum in the
literature.Comment: Paper 4 of 7 in series. 18 pages, 11 figures, as accepted in Ap
COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
We present early results from the COMAP Galactic Plane Survey conducted
between June 2019 and April 2021, spanning in Galactic
longitude and |b|<1.\!\!^{\circ}5 in Galactic latitude with an angular
resolution of . The full survey will span -
and will be the first large-scale radio continuum survey at
GHz with sub-degree resolution. We present initial results from the first part
of the survey, including diffuse emission and spectral energy distributions
(SEDs) of HII regions and supernova remnants. Using low and high frequency
surveys to constrain free-free and thermal dust emission contributions, we find
evidence of excess flux density at GHz in six regions that we interpret
as anomalous microwave emission. Furthermore we model UCHII contributions using
data from the GHz CORNISH catalogue and reject this as the cause of the
GHz excess. Six known supernova remnants (SNR) are detected at GHz,
and we measure spectral indices consistent with the literature or show evidence
of steepening. The flux density of the SNR W44 at GHz is consistent with
a power-law extrapolation from lower frequencies with no indication of spectral
steepening in contrast with recent results from the Sardinia Radio Telescope.
We also extract five hydrogen radio recombination lines to map the warm ionized
gas, which can be used to estimate electron temperatures or to constrain
continuum free-free emission. The full COMAP Galactic plane survey, to be
released in 2023/2024, will be an invaluable resource for Galactic
astrophysics.Comment: Paper 6 of 7 in series. 28 pages, 10 figures, submitted to Ap
COMAP Early Science: V. Constraints and Forecasts at
We present the current state of models for the carbon monoxide (CO)
line-intensity signal targeted by the CO Mapping Array Project (COMAP)
Pathfinder in the context of its early science results. Our fiducial model,
relating dark matter halo properties to CO luminosities, informs parameter
priors with empirical models of the galaxy-halo connection and previous CO(1-0)
observations. The Pathfinder early science data spanning wavenumbers
-Mpc represent the first direct 3D constraint on the
clustering component of the CO(1-0) power spectrum. Our 95% upper limit on the
redshift-space clustering amplitude K greatly
improves on the indirect upper limit of K reported from the CO
Power Spectrum Survey (COPSS) measurement at Mpc. The COMAP
limit excludes a subset of models from previous literature, and constrains
interpretation of the COPSS results, demonstrating the complementary nature of
COMAP and interferometric CO surveys. Using line bias expectations from our
priors, we also constrain the squared mean line intensity-bias product,
K, and the cosmic molecular gas
density, Mpc (95% upper
limits). Based on early instrument performance and our current CO signal
estimates, we forecast that the five-year Pathfinder campaign will detect the
CO power spectrum with overall signal-to-noise of 9-17. Between then and now,
we also expect to detect the CO-galaxy cross-spectrum using overlapping galaxy
survey data, enabling enhanced inferences of cosmic star-formation and
galaxy-evolution history.Comment: Paper 5 of 7 in series. 17 pages + appendix and bibliography (30
pages total); 15 figures, 6 tables; accepted for publication in ApJ; v3
reflects the accepted version with minor changes and additions to tex
COMAP Early Science: II. Pathfinder Instrument
Line intensity mapping (LIM) is a new technique for tracing the global
properties of galaxies over cosmic time. Detection of the very faint signals
from redshifted carbon monoxide (CO), a tracer of star formation, pushes the
limits of what is feasible with a total-power instrument. The CO Mapping
Project (COMAP) Pathfinder is a first-generation instrument aiming to prove the
concept and develop the technology for future experiments, as well as
delivering early science products. With 19 receiver channels in a hexagonal
focal plane arrangement on a 10.4 m antenna, and an instantaneous 26-34 GHz
frequency range with 2 MHz resolution, it is ideally suited to measuring
CO(=1-0) from . In this paper we discuss strategies for designing
and building the Pathfinder and the challenges that were encountered. The
design of the instrument prioritized LIM requirements over those of ancillary
science. After a couple of years of operation, the instrument is well
understood, and the first year of data is already yielding useful science
results. Experience with this Pathfinder will drive the design of the next
generations of experiments.Comment: Paper 2 of 7 in series. 27 pages, 28 figures, submitted to Ap
COMAP Early Science: I. Overview
The CO Mapping Array Project (COMAP) aims to use line intensity mapping of
carbon monoxide (CO) to trace the distribution and global properties of
galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate
the technologies and techniques needed for this goal, a Pathfinder instrument
has been constructed and fielded. Sensitive to CO(1-0) emission from
- and a fainter contribution from CO(2-1) at -8, the
Pathfinder is surveying deg in a 5-year observing campaign to detect
the CO signal from . Using data from the first 13 months of observing,
we estimate on scales - the first direct
3D constraint on the clustering component of the CO(1-0) power spectrum. Based
on these observations alone, we obtain a constraint on the amplitude of the
clustering component (the squared mean CO line temperature-bias product) of
K - nearly an order-of-magnitude improvement
on the previous best measurement. These constraints allow us to rule out two
models from the literature. We forecast a detection of the power spectrum after
5 years with signal-to-noise ratio (S/N) 9-17. Cross-correlation with an
overlapping galaxy survey will yield a detection of the CO-galaxy power
spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic
plane and present a preliminary map. Looking to the future of COMAP, we examine
the prospects for future phases of the experiment to detect and characterize
the CO signal from the EoR.Comment: Paper 1 of 7 in series. 18 pages, 16 figures, submitted to Ap