85 research outputs found
Separating intrinsic alignment and galaxy-galaxy lensing
The coherent physical alignment of galaxies is an important systematic for
gravitational lensing studies as well as a probe of the physical mechanisms
involved in galaxy formation and evolution. We develop a formalism for treating
this intrinsic alignment (IA) in the context of galaxy-galaxy lensing and
present an improved method for measuring IA contamination, which can arise when
sources physically associated with the lens are placed behind the lens due to
photometric redshift scatter. We apply the technique to recent Sloan Digital
Sky Survey (SDSS) measurements of Luminous Red Galaxy lenses and typical (L*)
source galaxies with photometric redshifts selected from the SDSS imaging data.
Compared to previous measurements, this method has the advantage of being fully
self-consistent in its treatment of the IA and lensing signals, solving for the
two simultaneously. We find an IA signal consistent with zero, placing tight
constraints on both the magnitude of the IA effect and its potential
contamination to the lensing signal. While these constraints depend on source
selection and redshift quality, the method can be applied to any measurement
that uses photometric redshifts. We obtain a model-independent upper-limit of
roughly 10% IA contamination for projected separations of approximately 0.1-100
Mpc/h. With more stringent photo-z cuts and reasonable assumptions about the
physics of intrinsic alignments, this upper limit is reduced to 1-2%. These
limits are well below the statistical error of the current lensing
measurements. Our results suggest that IA will not present intractable
challenges to the next generation of galaxy-galaxy lensing experiments, and the
methods presented here should continue to aid in our understanding of alignment
processes and in the removal of IA from the lensing signal.Comment: 31 pages, 8 Figures. Minor changes to reflect published versio
Generalized Automorphisms of Channel Codes: Properties, Code Design, and a Decoder
Low-density parity-check codes together with belief propagation (BP) decoding
are known to be well-performing for large block lengths. However, for short
block lengths there is still a considerable gap between the performance of the
BP decoder and the maximum likelihood decoder. Different ensemble decoding
schemes such as, e.g., the automorphism ensemble decoder (AED), can reduce this
gap in short block length regime. We propose a generalized AED (GAED) that uses
automorphisms according to the definition in linear algebra. Here, an
automorphism of a vector space is defined as a linear, bijective self-mapping,
whereas in coding theory self-mappings that are scaled permutations are
commonly used. We show that the more general definition leads to an explicit
joint construction of codes and automorphisms, and significantly enlarges the
search space for automorphisms of existing linear codes. Furthermore, we prove
the concept that generalized automorphisms can indeed be used to improve
decoding. Additionally, we propose a code construction of parity check codes
enabling the construction of codes with suitably designed automorphisms.
Finally, we analyze the decoding performances of the GAED for some of our
constructed codes.Comment: Submitted to IEEE Updated References. Corrected typos. Revised
argument in section 5, results unchange
Detecting Galaxy-Filament Alignments in the Sloan Digital Sky Survey III
Previous studies have shown the filamentary structures in the cosmic web
influence the alignments of nearby galaxies. We study this effect in the LOWZ
sample of the Sloan Digital Sky Survey using the "Cosmic Web Reconstruction"
filament catalogue. We find that LOWZ galaxies exhibit a small but
statistically significant alignment in the direction parallel to the
orientation of nearby filaments. This effect is detectable even in the absence
of nearby galaxy clusters, which suggests it is an effect from the matter
distribution in the filament. A nonparametric regression model suggests that
the alignment effect with filaments extends over separations of 30-40 Mpc. We
find that galaxies that are bright and early-forming align more strongly with
the directions of nearby filaments than those that are faint and late-forming;
however, trends with stellar mass are less statistically significant, within
the narrow range of stellar mass of this sample.Comment: 14 pages, 13 figures. Accepted to the MNRA
Systematic errors in weak lensing: application to SDSS galaxy-galaxy weak lensing
Weak lensing is emerging as a powerful observational tool to constrain
cosmological models, but is at present limited by an incomplete understanding
of many sources of systematic error. Many of these errors are multiplicative
and depend on the population of background galaxies. We show how the commonly
cited geometric test, which is rather insensitive to cosmology, can be used as
a ratio test of systematics in the lensing signal at the 1 per cent level. We
apply this test to the galaxy-galaxy lensing analysis of the Sloan Digital Sky
Survey (SDSS), which at present is the sample with the highest weak lensing
signal to noise and has the additional advantage of spectroscopic redshifts for
lenses. This allows one to perform meaningful geometric tests of systematics
for different subsamples of galaxies at different mean redshifts, such as
brighter galaxies, fainter galaxies and high-redshift luminous red galaxies,
both with and without photometric redshift estimates. We use overlapping
objects between SDSS and the DEEP2 and 2SLAQ spectroscopic surveys to establish
accurate calibration of photometric redshifts and to determine the redshift
distributions for SDSS. We use these redshift results to compute the projected
surface density contrast DeltaSigma around 259 609 spectroscopic galaxies in
the SDSS; by measuring DeltaSigma with different source samples we establish
consistency of the results at the 10 per cent level (1-sigma). We also use the
ratio test to constrain shear calibration biases and other systematics in the
SDSS survey data to determine the overall galaxy-galaxy weak lensing signal
calibration uncertainty. We find no evidence of any inconsistency among many
subsamples of the data.Comment: 39 pages, 19 figure
An Empirical Model For Intrinsic Alignments: Insights From Cosmological Simulations
We extend current models of the halo occupation distribution (HOD) to include
a flexible, empirical framework for the forward modeling of the intrinsic
alignment (IA) of galaxies. A primary goal of this work is to produce mock
galaxy catalogs for the purpose of validating existing models and methods for
the mitigation of IA in weak lensing measurements. This technique can also be
used to produce new, simulation-based predictions for IA and galaxy clustering.
Our model is probabilistically formulated, and rests upon the assumption that
the orientations of galaxies exhibit a correlation with their host dark matter
(sub)halo orientation or with their position within the halo. We examine the
necessary components and phenomenology of such a model by considering the
alignments between (sub)halos in a cosmological dark matter only simulation. We
then validate this model for a realistic galaxy population in a set of
simulations in the Illustris-TNG suite. We create an HOD mock with
Illustris-like correlations using our method, constraining the associated IA
model parameters, with the between our model's correlations
and those of Illustris matching as closely as 1.4 and 1.1 for
orientation--position and orientation--orientation correlation functions,
respectively. By modeling the misalignment between galaxies and their host
halo, we show that the 3-dimensional two-point position and orientation
correlation functions of simulated (sub)halos and galaxies can be accurately
reproduced from quasi-linear scales down to . We also find
evidence for environmental influence on IA within a halo. Our
publicly-available software provides a key component enabling efficient
determination of Bayesian posteriors on IA model parameters using observational
measurements of galaxy-orientation correlation functions in the highly
nonlinear regime.Comment: 17 pages, 12 figures, 3 tables, for submission to The Open Journal of
Astrophysics, code available at https://github.com/astropy/halotool
Wide-field Multi-object Spectroscopy to Enhance Dark Energy Science from LSST
LSST will open new vistas for cosmology in the next decade, but it cannot
reach its full potential without data from other telescopes. Cosmological
constraints can be greatly enhanced using wide-field ( deg total
survey area), highly-multiplexed optical and near-infrared multi-object
spectroscopy (MOS) on 4-15m telescopes. This could come in the form of
suitably-designed large surveys and/or community access to add new targets to
existing projects. First, photometric redshifts can be calibrated with high
precision using cross-correlations of photometric samples against spectroscopic
samples at that span thousands of sq. deg. Cross-correlations of
faint LSST objects and lensing maps with these spectroscopic samples can also
improve weak lensing cosmology by constraining intrinsic alignment systematics,
and will also provide new tests of modified gravity theories. Large samples of
LSST strong lens systems and supernovae can be studied most efficiently by
piggybacking on spectroscopic surveys covering as much of the LSST
extragalactic footprint as possible (up to square degrees).
Finally, redshifts can be measured efficiently for a high fraction of the
supernovae in the LSST Deep Drilling Fields (DDFs) by targeting their hosts
with wide-field spectrographs. Targeting distant galaxies, supernovae, and
strong lens systems over wide areas in extended surveys with (e.g.) DESI or MSE
in the northern portion of the LSST footprint or 4MOST in the south could
realize many of these gains; DESI, 4MOST, Subaru/PFS, or MSE would all be
well-suited for DDF surveys. The most efficient solution would be a new
wide-field, highly-multiplexed spectroscopic instrument in the southern
hemisphere with m aperture. In two companion white papers we present gains
from deep, small-area MOS and from single-target imaging and spectroscopy.Comment: Submitted to the call for Astro2020 science white papers; tables with
estimates of telescope time needed for a supernova host survey can be seen at
http://d-scholarship.pitt.edu/id/eprint/3604
BLIMP1 Is a Tumor Suppressor Gene Frequently Disrupted in Activated B Cell-like Diffuse Large B Cell Lymphoma
SummaryDiffuse large B cell lymphoma (DLBCL) is a heterogeneous disease composed of at least two distinct subtypes: germinal center B cell-like (GCB) and activated B cell-like (ABC) DLBCL. These phenotypic subtypes segregate with largely unique genetic lesions, suggesting the involvement of different pathogenetic mechanisms. In this report we show that the BLIMP1/PRDM1 gene is inactivated by multiple mechanisms, including homozygous deletions, truncating or missense mutations, and transcriptional repression by constitutively active BCL6, in ∼53% of ABC-DLBCL. In vivo, conditional deletion of Blimp1 in mouse B cells promotes the development of lymphoproliferative disorders recapitulating critical features of the human ABC-DLBCL. These results demonstrate that BLIMP1 is a bona fide tumor-suppressor gene whose loss contributes to lymphomagenesis by blocking plasma cell differentiation
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