339 research outputs found
Determining the HI content of galaxies via intensity mapping cross-correlations
We propose an innovative method for measuring the neutral hydrogen (HI)
content of an optically-selected spectroscopic sample of galaxies through
cross-correlation with HI intensity mapping measurements. We show that the
HI-galaxy cross-power spectrum contains an additive shot noise term which
scales with the average HI brightness temperature of the optically-selected
galaxies, allowing constraints to be placed on the average HI mass per galaxy.
This approach can estimate the HI content of populations too faint to directly
observe through their 21cm emission over a wide range of redshifts. This
cross-correlation, as a function of optical luminosity or colour, can be used
to derive HI-scaling relations. We demonstrate that this signal will be
detectable by cross-correlating upcoming Australian SKA Pathfinder (ASKAP)
observations with existing optically-selected samples. We also use
semi-analytic simulations to verify that the HI mass can be successfully
recovered by our technique in the range M_HI > 10^8 M_solar, in a manner
independent of the underlying power spectrum shape. We conclude that this
method is a powerful tool to study galaxy evolution, which only requires a
single intensity mapping dataset to infer complementary HI gas information from
existing optical and infra-red observations.Comment: 8 pages, 4 figures, submitted to MNRA
The varying w spread spectrum effect for radio interferometric imaging
We study the impact of the spread spectrum effect in radio interferometry on
the quality of image reconstruction. This spread spectrum effect will be
induced by the wide field-of-view of forthcoming radio interferometric
telescopes. The resulting chirp modulation improves the quality of
reconstructed interferometric images by increasing the incoherence of the
measurement and sparsity dictionaries. We extend previous studies of this
effect to consider the more realistic setting where the chirp modulation varies
for each visibility measurement made by the telescope. In these first
preliminary results, we show that for this setting the quality of
reconstruction improves significantly over the case without chirp modulation
and achieves almost the reconstruction quality of the case of maximal, constant
chirp modulation.Comment: 1 page, 1 figure, Proceedings of the Biomedical and Astronomical
Signal Processing Frontiers (BASP) workshop 201
Foreground Subtraction in Intensity Mapping with the SKA
21cm intensity mapping experiments aim to observe the diffuse neutral
hydrogen (HI) distribution on large scales which traces the Cosmic structure.
The Square Kilometre Array (SKA) will have the capacity to measure the 21cm
signal over a large fraction of the sky. However, the redshifted 21cm signal in
the respective frequencies is faint compared to the Galactic foregrounds
produced by synchrotron and free-free electron emission. In this article, we
review selected foreground subtraction methods suggested to effectively
separate the 21cm signal from the foregrounds with intensity mapping
simulations or data. We simulate an intensity mapping experiment feasible with
SKA phase 1 including extragalactic and Galactic foregrounds. We give an
example of the residuals of the foreground subtraction with a independent
component analysis and show that the angular power spectrum is recovered within
the statistical errors on most scales. Additionally, the scale of the Baryon
Acoustic Oscillations is shown to be unaffected by foreground subtraction.Comment: This article is part of the 'SKA Cosmology Chapter, Advancing
Astrophysics with the SKA (AASKA14), Conference, Giardini Naxos (Italy), June
9th-13th 2014
On the Parity Problem in One-Dimensional Cellular Automata
We consider the parity problem in one-dimensional, binary, circular cellular
automata: if the initial configuration contains an odd number of 1s, the
lattice should converge to all 1s; otherwise, it should converge to all 0s. It
is easy to see that the problem is ill-defined for even-sized lattices (which,
by definition, would never be able to converge to 1). We then consider only odd
lattices.
We are interested in determining the minimal neighbourhood that allows the
problem to be solvable for any initial configuration. On the one hand, we show
that radius 2 is not sufficient, proving that there exists no radius 2 rule
that can possibly solve the parity problem from arbitrary initial
configurations. On the other hand, we design a radius 4 rule that converges
correctly for any initial configuration and we formally prove its correctness.
Whether or not there exists a radius 3 rule that solves the parity problem
remains an open problem.Comment: In Proceedings AUTOMATA&JAC 2012, arXiv:1208.249
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
"Food Addiction" in Patients with Eating Disorders is Associated with Negative Urgency and Difficulties to Focus on Long-Term Goals
Objectives: The present study aimed to investigate if eating disorder patients differ in specific personality traits depending on a positive screening of food addiction (FA) and to find a model to predict FA in eating disorder patients using measures of personality and impulsivity. Methods : Two hundred seventy eight patients, having an eating disorder, self-reported on FA, impulsivity, personality, eating and general psychopathology. Patients were then split into two groups, depending on a positive or negative result on the FA screening. Analysis of variance was used to compare means between the two groups. Stepwise binary logistic regression was used to obtain a predictive model for the presence of FA. Results: Patients with FA had lower self-directedness, and more negative urgency and lack of perseverance than patients not reporting addictive eating. The probability of FA can be predicted by high negative urgency, high reward dependence, and low lack of premeditation. Conclusion: Eating disorder patients who have more problems to pursue tasks to the end and to focus on long-term goals seem to be more likely to develop addictive eating patterns
'Food Addiction' in Patients with Eating Disorders is Associated with Negative Urgency and Difficulties to Focus on Long-Term Goals
Objectives: The present study aimed to investigate if eating disorder patients differ in specific personality traits depending on a positive screening of food addiction (FA) and to find a model to predict FA in eating disorder patients using measures of personality and impulsivity. Methods: Two hundred seventy eight patients, having an eating disorder, self-reported on FA, impulsivity, personality, eating and general psychopathology. Patients were then split into two groups, depending on a positive or negative result on the FA screening. Analysis of variance was used to compare means between the two groups. Stepwise binary logistic regression was used to obtain a predictive model for the presence of FA. Results: Patients with FA had lower self-directedness, and more negative urgency and lack of perseverance than patients not reporting addictive eating. The probability of FA can be predicted by high negative urgency, high reward dependence, and low lack of premeditation. Conclusion: Eating disorder patients who have more problems to pursue tasks to the end and to focus on long-term goals seem to be more likely to develop addictive eating patterns
Cosmology with a SKA HI intensity mapping survey
Advancing Astrophysics with the Square Kilometre Array
June 8-13, 2014
Giardini Naxos, ItalyHI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of
the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI
as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of
the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve
individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity
maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the
baryon acoustic oscillation and redshift space distortion features in the matter power spectrum –
thus determining the expansion and growth history of the Universe – these surveys can provide
powerful tests of dark energy models and modifications to General Relativity. They can also be
used to probe physics on extremely large scales, where precise measurements of spatial curvature
and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring
the sum of neutrino masses; and at high redshifts where non-standard evolution models can be
probed. We discuss the impact of foregrounds as well as various instrumental and survey design
parameters on the achievable constraints. In particular we analyse the feasibility of using the
SKA1 autocorrelations to probe the large-scale signal.Web of Scienc
Star/galaxy separation at faint magnitudes: application to a simulated Dark Energy Survey
We address the problem of separating stars from galaxies in future large photometric surveys. We focus our analysis on simulations of the Dark Energy Survey (DES). In the first part of the paper, we derive the science requirements on star/galaxy separation, for measurement of the cosmological parameters with the gravitational weak lensing and large-scale structure probes. These requirements are dictated by the need to control both the statistical and systematic errors on the cosmological parameters, and by point spread function calibration. We formulate the requirements in terms of the completeness and purity provided by a given star/galaxy classifier. In order to achieve these requirements at faint magnitudes, we propose a new method for star/galaxy separation in the second part of the paper. We first use principal component analysis to outline the correlations between the objects parameters and extract from it the most relevant information. We then use the reduced set of parameters as input to an Artificial Neural Network. This multiparameter approach improves upon purely morphometric classifiers (such as the classifier implemented in SExtractor), especially at faint magnitudes: it increases the purity by up to 20 per cent for stars and by up to 12 per cent for galaxies, at i-magnitude fainter than 2
The EREBOS project -- Investigating the effect of substellar and low-mass stellar companions on late stellar evolution
Eclipsing post-common envelope binaries are highly important for resolving
the poorly understood, very short-lived common envelope phase. Most hot
subdwarfs (sdO/Bs) are the bare He-burning cores of red giants which have lost
almost all of their hydrogen envelopes. This mass loss is often triggered by
common envelope interactions with close stellar or even sub-stellar companions.
In the recently published catalog of eclipsing binaries in the Galactic Bulge
and in the ATLAS survey, we discovered 161 new eclipsing systems showing a
reflection effect by visual inspection of the light curves and using a
machine-learning algorithm. The EREBOS (Eclipsing Reflection Effect Binaries
from Optical Surveys) project aims at analyzing all newly discovered eclipsing
binaries with reflection effect based on a spectroscopic and photometric follow
up. To constrain the nature of the primary we derived the absolute magnitude
and the reduced proper motion of all our targets with the help of the
parallaxes and proper motions measured by the Gaia mission and compared those
to the Gaia white dwarf catalogue. For a sub-set of our targets with observed
spectra the nature could be derived by measuring the atmospheric parameter of
the primary confirming that less than 10\% of our systems are not sdO/Bs with
cool companions but white dwarfs or central stars of planetary nebula. This
large sample of eclipsing hot subdwarfs with cool companions allowed us to
derive a significant period distribution for hot subdwarfs with cool companions
for the first time showing that the period distribution is much broader than
previously thought and ideally suited to find the lowest mass companions to hot
subdwarf stars. In the future several new photometric surveys will be carried
out, which will increase the sample of this project even more giving the
potential to test many aspects of common envelope theory and binary evolution.Comment: accepted in A&A, 29 pages, 18 figure
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