225 research outputs found
Type Ia supernova Hubble diagram with near-infrared and optical observations
We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature. The
analysis of 45 well-sampled NIR LCs shows that a single template accurately
describes them if its time axis is stretched with the optical stretch
parameter. This allows us to estimate the NIR peak magnitudes even with one
observation obtained within 10 days from B-band maximum. We find that the NIR
Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first
time we report a possible dependence on the J_max-H_max color. The intrinsic
NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is
smaller than what can be derived for a similarly heterogeneous sample at
optical wavelengths. In conclusion, we find that SNe Ia are at least as good
standard candles in the NIR as in the optical. We showed that it is feasible to
extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the
NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that
the most efficient way to extend the NIR Hubble diagram to high redshift would
be to obtain a single observation close to the NIR maximum. (abridged)Comment: 39 pages, 15 figures, accepted by A&
Model selection applied to reconstruction of the Primordial Power Spectrum
The preferred shape for the primordial spectrum of curvature perturbations is
determined by performing a Bayesian model selection analysis of cosmological
observations. We first reconstruct the spectrum modelled as piecewise linear in
\log k between nodes in k-space whose amplitudes and positions are allowed to
vary. The number of nodes together with their positions are chosen by the
Bayesian evidence, so that we can both determine the complexity supported by
the data and locate any features present in the spectrum. In addition to the
node-based reconstruction, we consider a set of parameterised models for the
primordial spectrum: the standard power-law parameterisation, the spectrum
produced from the Lasenby & Doran (LD) model and a simple variant
parameterisation. By comparing the Bayesian evidence for different classes of
spectra, we find the power-law parameterisation is significantly disfavoured by
current cosmological observations, which show a preference for the LD model.Comment: Minor changes to match version accepted by JCA
Measuring primordial gravitational waves from CMB B-modes in cosmologies with generalized expansion histories
We evaluate our capability to constrain the abundance of primordial tensor
perturbations in cosmologies with generalized expansion histories in the epoch
of cosmic acceleration. Forthcoming satellite and sub-orbital experiments
probing polarization in the CMB are expected to measure the B-mode power in CMB
polarization, coming from PGWs on the degree scale, as well as gravitational
lensing on arcmin scales; the latter is the main competitor for the measurement
of PGWs, and is directly affected by the underlying expansion history,
determined by the presence of a DE component. In particular, we consider early
DE possible scenarios, in which the expansion history is substantially modified
at the epoch in which the CMB lensing is most relevant. We show that the
introduction of a parametrized DE may induce a variation as large as 30% in the
ratio of the power of lensing and PGWs on the degree scale. We find that
adopting the nominal specifications of upcoming satellite measurements the
constraining power on PGWs is weakened by the inclusion of the extra degrees of
freedom, resulting in a reduction of about 10% of the upper limits on r in
fiducial models with no GWs, as well as a comparable increase in the error bars
in models with non-zero r. Moreover, we find that the inclusion of sub-orbital
CMB experiments, capable of mapping the B-mode power up to the angular scales
affected by lensing, can restore the forecasted performances with a
cosmological constant. Finally, we show how the combination of CMB data with
Type Ia SNe, BAO and Hubble constant allows to constrain simultaneously r and
the DE quantities in the parametrization we consider, consisting of present
abundance and first redshift derivative of the energy density. We compare this
study with results obtained using the forecasted lensing potential measurement
precision from CMB satellite observations, finding consistent results.Comment: 17 pages, 9 figures, accepted for publication by JCAP. Modified
version after the referee's comment
Survey strategy optimization for the Atacama Cosmology Telescope
In recent years there have been significant improvements in the sensitivity
and the angular resolution of the instruments dedicated to the observation of
the Cosmic Microwave Background (CMB). ACTPol is the first polarization
receiver for the Atacama Cosmology Telescope (ACT) and is observing the CMB sky
with arcmin resolution over about 2000 sq. deg. Its upgrade, Advanced ACTPol
(AdvACT), will observe the CMB in five frequency bands and over a larger area
of the sky. We describe the optimization and implementation of the ACTPol and
AdvACT surveys. The selection of the observed fields is driven mainly by the
science goals, that is, small angular scale CMB measurements, B-mode
measurements and cross-correlation studies. For the ACTPol survey we have
observed patches of the southern galactic sky with low galactic foreground
emissions which were also chosen to maximize the overlap with several galaxy
surveys to allow unique cross-correlation studies. A wider field in the
northern galactic cap ensured significant additional overlap with the BOSS
spectroscopic survey. The exact shapes and footprints of the fields were
optimized to achieve uniform coverage and to obtain cross-linked maps by
observing the fields with different scan directions. We have maximized the
efficiency of the survey by implementing a close to 24 hour observing strategy,
switching between daytime and nighttime observing plans and minimizing the
telescope idle time. We describe the challenges represented by the survey
optimization for the significantly wider area observed by AdvACT, which will
observe roughly half of the low-foreground sky. The survey strategies described
here may prove useful for planning future ground-based CMB surveys, such as the
Simons Observatory and CMB Stage IV surveys.Comment: 14 Pages, 9 Figures, 4 Table
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
The Atacama Cosmology Telescope: Cross Correlation with Planck maps
We present the temperature power spectrum of the Cosmic Microwave Background
obtained by cross-correlating maps from the Atacama Cosmology Telescope (ACT)
at 148 and 218 GHz with maps from the Planck satellite at 143 and 217 GHz, in
two overlapping regions covering 592 square degrees. We find excellent
agreement between the two datasets at both frequencies, quantified using the
variance of the residuals between the ACT power spectra and the ACTxPlanck
cross-spectra. We use these cross-correlations to calibrate the ACT data at 148
and 218 GHz, to 0.7% and 2% precision respectively. We find no evidence for
anisotropy in the calibration parameter. We compare the Planck 353 GHz power
spectrum with the measured amplitudes of dust and cosmic infrared background
(CIB) of ACT data at 148 and 218 GHz. We also compare planet and point source
measurements from the two experiments.Comment: 9 pages, 8 figure
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
The Atacama Cosmology Telescope: A Measurement of the 600< ell <8000 Cosmic Microwave Background Power Spectrum at 148 GHz
We present a measurement of the angular power spectrum of the cosmic
microwave background (CMB) radiation observed at 148 GHz. The measurement uses
maps with 1.4' angular resolution made with data from the Atacama Cosmology
Telescope (ACT). The observations cover 228 square degrees of the southern sky,
in a 4.2-degree-wide strip centered on declination 53 degrees South. The CMB at
arcminute angular scales is particularly sensitive to the Silk damping scale,
to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by
radio sources and dusty galaxies. After masking the 108 brightest point sources
in our maps, we estimate the power spectrum between 600 < \ell < 8000 using the
adaptive multi-taper method to minimize spectral leakage and maximize use of
the full data set. Our absolute calibration is based on observations of Uranus.
To verify the calibration and test the fidelity of our map at large angular
scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP
power spectrum from 250 < ell < 1150. The power beyond the Silk damping tail of
the CMB is consistent with models of the emission from point sources. We
quantify the contribution of SZ clusters to the power spectrum by fitting to a
model normalized at sigma8 = 0.8. We constrain the model's amplitude ASZ < 1.63
(95% CL). If interpreted as a measurement of sigma8, this implies sigma8^SZ <
0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly
to a 6-parameter LCDM model plus terms for point sources and the SZ effect is
consistent with these results.Comment: 15 pages, 8 figures. Accepted for publication in Ap
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