We present a precise measurement of cosmological time dilation using the
light curves of 1504 type Ia supernovae from the Dark Energy Survey spanning a
redshift range $0.1\lesssim z\lesssim 1.2$. We ...find that the width of supernova
light curves is proportional to $(1+z)$, as expected for time dilation due to
the expansion of the Universe. Assuming type Ia supernovae light curves are
emitted with a consistent duration $\Delta t_{\rm em}$, and parameterising the
observed duration as $\Delta t_{\rm obs}=\Delta t_{\rm em}(1+z)^b$, we fit for
the form of time dilation using two methods. Firstly, we find that a power of
$b \approx 1$ minimises the flux scatter in stacked subsamples of light curves
across different redshifts. Secondly, we fit each target supernova to a stacked
light curve (stacking all supernovae with observed bandpasses matching that of
the target light curve) and find $b=1.003\pm0.005$ (stat) $\pm\,0.010$ (sys).
Thanks to the large number of supernovae and large redshift-range of the
sample, this analysis gives the most precise measurement of cosmological time
dilation to date, ruling out any non-time-dilating cosmological models at very
high significance.
We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in \(\sim 5000 \deg^2\) from the first three years of imaging data from the Dark Energy Survey (DES). Based ...on a single-component Sérsic model fit, we define extended LSBGs as galaxies with \(g\)-band effective radii \(R_{eff}(g) > 2.5''\) and mean surface brightness \(\bar{\mu}_{eff}(g) > 24.2 \,mag ȧrcsec^{-2}\). We find that the distribution of LSBGs is strongly bimodal in \((g-r)\) vs.\ \((g-i\)) color space. We divide our sample into red (\(g-i \geq 0.60\)) and blue (\(g-i<0.60\)) galaxies and study the properties of the two populations. Redder LSBGs are more clustered than their blue counterparts and are correlated with the distribution of nearby (\(z < 0.10\)) bright galaxies. Red LSBGs constitute \(\sim 33\%\) of our LSBG sample, and \(\sim 30\%\) of these are located within 1 deg of low-redshift galaxy groups and clusters (compared to \(\sim 8\%\) of the blue LSBGs). For nine of the most prominent galaxy groups and clusters, we calculate the physical properties of associated LSBGs assuming a redshift derived from the host system. In these systems, we identify 41 objects that can be classified as ultra-diffuse galaxies, defined as LSBGs with projected physical effective radii \(R_{eff} > 1.5 \,kpc\) and central surface brighthness \(\mu_0(g) > 24.0\, mag \,arcsec^{-2}\). The wide-area sample of LSBGs in DES can be used to test the role of environment on models of LSBG formation and evolution.
We present angular diameter measurements obtained by measuring the position of Baryon Acoustic Oscillations (BAO) in an optimised sample of galaxies from the first three years of Dark Energy Survey ...data (DES Y3). The sample consists of 7 million galaxies distributed over a footprint of 4100 deg\(^2\) with \(0.6 < z_{\rm photo} < 1.1\) and a typical redshift uncertainty of \(0.03(1+z)\). The sample selection is the same as in the BAO measurement with the first year of DES data, but the analysis presented here uses three times the area, extends to higher redshift and makes a number of improvements, including a fully analytical BAO template, the use of covariances from both theory and simulations, and an extensive pre-unblinding protocol. We used two different statistics: angular correlation function and power spectrum, and validate our pipeline with an ensemble of over 1500 realistic simulations. Both statistics yield compatible results. We combine the likelihoods derived from angular correlations and spherical harmonics to constrain the ratio of comoving angular diameter distance \(D_M\) at the effective redshift of our sample to the sound horizon scale at the drag epoch. We obtain \(D_M(z_{\rm eff}=0.835)/r_{\rm d} = 18.92 \pm 0.51\), which is consistent with, but smaller than, the Planck prediction assuming flat \lcdm, at the level of \(2.3 \sigma\). The analysis was performed blind and is robust to changes in a number of analysis choices. It represents the most precise BAO distance measurement from imaging data to date, and is competitive with the latest transverse ones from spectroscopic samples at \(z>0.75\). When combined with DES 3x2pt + SNIa, they lead to improvements in \(H_0\) and \(\Omega_m\) constraints by \(\sim 20\%\)
In a case-control study, we tested the hypothesis that the genetically determined ability to metabolize debrisoquine is related to risk of lung cancer. Overall, individuals who were extensive ...metabolizers of debrisoquine were at significantly greater risk of lung cancer than those who were poor or intermediate metabolizers (odds ratio = 6.1; 95% confidence interval = 2.2-17.1). In this study, case patients had lung cancer, and control subjects had either chronic obstructive pulmonary disease or cancers other than lung cancer. Results were adjusted for age, race, asbestos exposure, and smoking. Both black and white individuals who were extensive metabolizers of debrisoquine were at significantly increased risk after similar adjustment (for blacks, odds ratio = 4.5, 95% confidence interval = 1.1-18.1; for whites, odds ratio = 10.2, 95% confidence interval = 2.0-51.4). Significantly increased risk of lung cancer was also present for individuals who were extensive metabolizers when subjects with chronic obstructive pulmonary disease or other cancers were considered separately. These data confirm that the ability to metabolize debrisoquine is a major determinant of susceptibility to lung cancer. Evaluation of the marker in other case-control settings, further exploration of racial differences, and the prospective evaluation of this marker in subgroups at high risk of lung cancer are areas worthy of further study.
Clusters of galaxies are sensitive to the most nonlinear peaks in the cosmic density field. The weak gravitational lensing of background galaxies by clusters can allow us to infer their masses. ...However, galaxies associated with the local environment of the cluster can also be intrinsically aligned due to the local tidal gradient, contaminating any cosmology derived from the lensing signal. We measure this intrinsic alignment in Dark Energy Survey (DES) Year 1 redMaPPer clusters. We find evidence of a non-zero mean radial alignment of galaxies within clusters between redshift 0.1-0.7. We find a significant systematic in the measured ellipticities of cluster satellite galaxies that we attribute to the central galaxy flux and other intracluster light. We attempt to correct this signal, and fit a simple model for intrinsic alignment amplitude (\(A_{\textrm{IA}}\)) to the measurement, finding \(A_{\textrm{IA}}=0.15\pm 0.04\), when excluding data near the edge of the cluster. We find a significantly stronger alignment of the central galaxy with the cluster dark matter halo at low redshift and with higher richness and central galaxy absolute magnitude (proxies for cluster mass). This is an important demonstration of the ability of large photometric data sets like DES to provide direct constraints on the intrinsic alignment of galaxies within clusters. These measurements can inform improvements to small-scale modeling and simulation of the intrinsic alignment of galaxies to help improve the separation of the intrinsic alignment signal in weak lensing studies.
Stochastic field distortions caused by atmospheric turbulence are a fundamental limitation to the astrometric accuracy of ground-based imaging. This distortion field is measurable at the locations of ...stars with accurate positions provided by the Gaia DR2 catalog; we develop the use of Gaussian process regression (GPR) to interpolate the distortion field to arbitrary locations in each exposure. We introduce an extension to standard GPR techniques that exploits the knowledge that the 2-dimensional distortion field is curl-free. Applied to several hundred 90-second exposures from the Dark Energy Survey as a testbed, we find that the GPR correction reduces the variance of the turbulent distortions \(\approx12\times\), on average, with better performance in denser regions of the Gaia catalog. The RMS per-coordinate distortion in the \(riz\) bands is typically \(\approx7\) mas before any correction, and \(\approx2\) mas after application of the GPR model. The GPR astrometric corrections are validated by the observation that their use reduces, from 10 to 5 mas RMS, the residuals to an orbit fit to \(riz\)-band observations over 5 years of the \(r=18.5\) trans-Neptunian object Eris. We also propose a GPR method, not yet implemented, for simultaneously estimating the turbulence fields and the 5-dimensional stellar solutions in a stack of overlapping exposures, which should yield further turbulence reductions in future deep surveys.
Current and future cosmological analyses with Type Ia Supernovae (SNe Ia) face three critical challenges: i) measuring redshifts from the supernova or its host galaxy; ii) classifying SNe without ...spectra; and iii) accounting for correlations between the properties of SNe Ia and their host galaxies. We present here a novel approach that addresses each challenge. In the context of the Dark Energy Survey (DES), we analyze a SNIa sample with host galaxies in the redMaGiC galaxy catalog, a selection of Luminous Red Galaxies. Photo-\(z\) estimates for these galaxies are expected to be accurate to \(\sigma_{\Delta z/(1+z)}\sim0.02\). The DES-5YR photometrically classified SNIa sample contains approximately 1600 SNe and 125 of these SNe are in redMaGiC galaxies. We demonstrate that redMaGiC galaxies almost exclusively host SNe Ia, reducing concerns with classification uncertainties. With this subsample, we find similar Hubble scatter (to within \(\sim0.01\) mag) using photometric redshifts in place of spectroscopic redshifts. With detailed simulations, we show the bias due to using photo-\(z\)s from redMaGiC host galaxies on the measurement of the dark energy equation-of-state \(w\) is up to \(\Delta w \sim 0.01-0.02\). With real data, we measure a difference in \(w\) when using redMaGiC photometric redshifts versus spectroscopic redshifts of \(\Delta w = 0.005\). Finally, we discuss how SNe in redMaGiC galaxies appear to be a more standardizable population due to a weaker relation between color and luminosity (\(\beta\)) compared to the DES-3YR population by \(\sim5\sigma\); this finding is consistent with predictions that redMaGiC galaxies exhibit lower reddening ratios (\(\textrm{R}_\textrm{V}\)) than the general population of SN host galaxies. These results establish the feasibility of performing redMaGiC SN cosmology with photometric survey data in the absence of spectroscopic data.
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