119 research outputs found
Cosmological Information in the Intrinsic Alignments of Luminous Red Galaxies
The intrinsic alignments of galaxies are usually regarded as a contaminant to
weak gravitational lensing observables. The alignment of Luminous Red Galaxies,
detected unambiguously in observations from the Sloan Digital Sky Survey, can
be reproduced by the linear tidal alignment model of Catelan, Kamionkowski &
Blandford (2001) on large scales. In this work, we explore the cosmological
information encoded in the intrinsic alignments of red galaxies. We make
forecasts for the ability of current and future spectroscopic surveys to
constrain local primordial non-Gaussianity and Baryon Acoustic Oscillations
(BAO) in the cross-correlation function of intrinsic alignments and the galaxy
density field. For the Baryon Oscillation Spectroscopic Survey, we find that
the BAO signal in the intrinsic alignments is marginally significant with a
signal-to-noise ratio of 1.8 and 2.2 with the current LOWZ and CMASS samples of
galaxies, respectively, and increasing to 2.3 and 2.7 once the survey is
completed. For the Dark Energy Spectroscopic Instrument and for a spectroscopic
survey following the EUCLID redshift selection function, we find
signal-to-noise ratios of 12 and 15, respectively. Local type primordial
non-Gaussianity, parametrized by fNL = 10, is only marginally significant in
the intrinsic alignments signal with signal-to-noise ratios < 2 for the three
surveys considered.Comment: 20 pages, 13 figures, version accepted to JCA
Can weak lensing surveys confirm BICEP2 ?
The detection of B-modes in the Cosmic Microwave Background (CMB)
polarization by the BICEP2 experiment, if interpreted as evidence for a
primordial gravitational wave background, has enormous ramifications for
cosmology and physics. It is crucial to test this hypothesis with independent
measurements. A gravitational wave background leads to B-modes in galaxy shape
correlations (shear) both through lensing and tidal alignment effects. Since
the systematics and foregrounds of galaxy shapes and CMB polarization are
entirely different, a detection of a cross-correlation between the two
observables would provide conclusive proof for the existence of a primordial
gravitational wave background. We find that upcoming weak lensing surveys will
be able to detect the cross-correlation between B-modes of the CMB and galaxy
shapes. However, this detection is not sufficient to confirm or falsify the
hypothesis of a primordial origin for CMB B-mode polarization.Comment: 7 pages, 3 figures, published in PR
Lensing bias on cosmological parameters from bright standard sirens
Next generation gravitational waves (GWs) observatories are expected to
measure GW signals with unprecedented sensitivity, opening new, independent
avenues to learn about our Universe. The distance-redshift relation is a
fulcrum for cosmology and can be tested with GWs emitted by merging binaries of
compact objects, called standard sirens, thanks to the fact that they provide
the absolute distance from the source. On the other hand, fluctuations of the
intervening matter density field induce modifications on the measurement of
luminosity distance compared to that of a homogeneous universe. Assuming that
the redshift information is obtained through the detection of an
electromagnetic counterpart, we investigate the impact that lensing of GWs
might have in the inference of cosmological parameters. We treat lensing as a
systematic error and check for residual bias on the values of the cosmological
parameters. We do so by means of mock catalogues of bright sirens events in
different scenarios relevant to Einstein Telescope. For our fiducial scenario,
the lensing bias can be comparable to or greater than the expected statistical
uncertainty of the cosmological parameters, although non-negligible
fluctuations in the bias values are observed for different realisations of the
mock catalogue. We also discuss some mitigation strategies that can be adopted
in the data analysis. Overall, our work highlights the need to model lensing
effects when using standard sirens as probes of the distance-redshift relation.Comment: 15 pages, 14 figure
Contamination of early-type galaxy alignments to galaxy lensing-CMB lensing cross-correlation
Galaxy shapes are subject to distortions due to the tidal field of the
Universe. The cross-correlation of galaxy lensing with the lensing of the
Cosmic Microwave Background (CMB) cannot easily be separated from the
cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work
suggested that the intrinsic alignment contamination can be of this
cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope
surveys. Here we re-examine these estimates using up-to-date observational
constraints of intrinsic alignments at a redshift more similar to that of CS82
galaxies. We find a contamination of the cross-spectrum from
red galaxies, with uncertainty due to uncertainties in the
redshift distribution of source galaxies and the modelling of the spectral
energy distribution. Blue galaxies are consistent with being unaligned, but
could contaminate the cross-spectrum by an additional within current
confidence levels. While our fiducial estimate of alignment
contamination is similar to previous work, our work suggests that the relevance
of alignments for CMB lensing-galaxy lensing cross-correlation remains largely
unconstrained. Little information is currently available about alignments at
. We consider the upper limiting case where all galaxies are
aligned with the same strength as low redshift luminous red galaxies, finding
as much as contamination.Comment: 11 pages, 3 figures, MNRAS submitte
Caught in the rhythm: how satellites settle into a plane around their central galaxy
Using the cosmological hydrodynamics simulation Horizon-AGN, we investigate
the spatial distribution of satellite galaxies relative to their central
counterpart in the redshift range between 0.3 and 0.8. We find that, on
average, these satellites tend to be located on the galactic plane of the
central object. This effect is detected for central galaxies with a stellar
mass larger than 10^10 solar masses and found to be strongest for red passive
galaxies, while blue galaxies exhibit a weaker trend. For galaxies with a minor
axis parallel to the direction of the nearest filament, we find that the
coplanarity is stronger in the vicinity of the central galaxy, and decreases
when moving towards the outskirts of the host halo. By contrast, the spatial
distribution of satellite galaxies relative to their closest filament follows
the opposite trend: their tendency to align with them dominates at large
distances from the central galaxy, and fades away in its vicinity. Relying on
mock catalogs of galaxies in that redshift range, we show that massive red
centrals with a spin perpendicular to their filament also have corotating
satellites well aligned with both the galactic plane and the filament. On the
other hand, lower-mass blue centrals with a spin parallel to their filament
have satellites flowing straight along this filament, and hence orthogonally to
their galactic plane. The orbit of these satellites is then progressively bent
towards a better alignment with the galactic plane as they penetrate the
central region of their host halo. The kinematics previously described are
consistent with satellite infall and spin build-up via quasi-polar flows,
followed by a re-orientation of the spin of massive red galaxies through
mergers.Comment: 26 pages, 28 figures, 2 tables, submitted to A&
Intrinsic alignments of group and cluster galaxies in photometric surveys
Intrinsic alignments of galaxies have been shown to contaminate weak
gravitational lensing observables on linear scales, 10 Mpc, but
studies of alignments in the non-linear regime have thus far been inconclusive.
We present an estimator for extracting the intrinsic alignment signal of
galaxies around stacked clusters of galaxies from multiband imaging data. Our
estimator removes the contamination caused by galaxies that are gravitationally
lensed by the clusters and scattered in redshift space due to photometric
redshift uncertainties. It uses posterior probability distributions for the
redshifts of the galaxies in the sample and it is easily extended to obtain the
weak gravitational lensing signal while removing the intrinsic alignment
contamination. We apply this algorithm to groups and clusters of galaxies
identified in the Sloan Digital Sky Survey `Stripe 82' coadded imaging data
over deg. We find that the intrinsic alignment signal around
stacked clusters in the redshift range is consistent with zero. In
terms of the tidal alignment model of Catelan et al. (2001), we set joint
constraints on the strength of the alignment and the bias of the lensing groups
and clusters on scales between 0.1 and Mpc, . This constrains the contamination fraction of
alignment to lensing signal to the range between per cent below
scales of 1 Mpc at 95 per cent confidence level, and this result
depends on our photometric redshift quality and selection criteria used to
identify background galaxies. Our results are robust to the choice of
photometric band in which the shapes are measured ( and ) and to centring
on the Brightest Cluster Galaxy or on the geometrical centre of the clusters.Comment: 30 pages, 16 figures, published in MNRA
The alignment of galaxies at the Baryon Acoustic Oscillation scale
Massive elliptical galaxies align pointing their major axis towards each
other in the structure of the Universe. Such alignments are well-described at
large scales through a linear relation with respect to the tidal field of the
large-scale structure. At such scales, galaxy alignments are sensitive to the
presence of baryon acoustic oscillations (BAO). The shape of the BAO feature in
galaxy alignment correlations differs from the traditional peak in the
clustering correlation function. Instead, it appears as a trough feature at the
BAO scale. In this work, we show that this feature can be explained by a simple
toy model of tidal fields from a spherical shell of matter. This helps give a
physical insight for the feature and highlights the need for tailored
template-based identification methods for the BAO in alignment statistics. We
also discuss the impact of projection baselines and photometric redshift
uncertainties for identifying the BAO in intrinsic alignment measurements.Comment: 12 pages, 9 figures, OJA versio
Vortex dipolar structures in a rigid model of the larynx at flow onset
Starting jet airflow is investigated in a channel with a pair of consecutive slitted constrictions approximating the true and false vocal folds in the human larynx. The flow is visualized using the Schlieren optical technique and simulated by solving the Navier-Stokes equations for an incompressible two-dimensional viscous flow. Laboratory and numerical experiments show the spontaneous formation of three different classes of vortex dipolar structures in several regions of the laryngeal profile under conditions that may be assimilated to those of voice onset.Fil: Chisari, Nora Elisa. University of Princeton; Estados Unidos. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Artana, Guillermo Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Sciamarella, D.. Centre National de la Recherche Scientifique; Franci
Impact of intrinsic alignments on clustering constraints of the growth rate
Intrinsic alignments between galaxies and the large-scale structure contaminate galaxy clustering analyses and impact constraints on galaxy bias and the growth rate of structure in the Universe. This is the result of alignments inducing a selection effect on spectroscopic samples which is correlated with the large-scale structure. In this work, we quantify the biases on galaxy bias and the growth rate when alignments are neglected. We also examine different options for the mitigation of alignments by considering external priors on the effect and different probe combinations. We find that conservative analyses that restrict to k(max) = 0.1 Mpc(-1) are not significantly affected. However, analyses that aim to go to higher wave numbers could evidence a significant contamination from alignments. In those cases, including a prior on alignment amplitude, or combining clustering with the position-intrinsic shape correlation of galaxies, can recover the same expected constraining power, or even inform bias and growth rate measurements
The impact of self-interacting dark matter on the intrinsic alignments of galaxies
The formation and evolution of galaxies is known to be sensitive to tidal processes leading to intrinsic correlations between their shapes and orientations. Such correlations can be measured to high significance today, suggesting that cosmological information can be extracted from them. Among the most pressing questions in particle physics and cosmology is the nature of dark matter. If dark matter is self-interacting, it can leave an imprint on galaxy shapes. In this work, we investigate whether self-interactions can produce a long-lasting imprint on intrinsic galaxy shape correlations. We investigate this observable at low redshift (z < 0.4) using a state-of-the-art suite of cosmological hydro-dynamical simulations where the dark matter model is varied. We find that dark matter self-interactions induce a mass-dependent suppression in the intrinsic alignment signal by up to 50 per cent out to tens of mega-parsecs, showing that self-interactions can impact structure outside the very core of clusters. We find evidence that self-interactions have a scale-dependent impact on the intrinsic alignment signal that is sufficiently different from signatures introduced by differing baryonic physics prescriptions, suggesting that it is detectable with upcoming all-sky surveys
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