8 research outputs found
The effect of environment on Type Ia supernovae in the Dark Energy Survey three-year cosmological sample
Analyses of Type Ia supernovae (SNe Ia) have found puzzling correlations between their standardized luminosities and host galaxy properties: SNe Ia in high-mass, passive hosts appear brighter than those in lower mass, star-forming hosts. We examine the host galaxies of SNe Ia in the Dark Energy Survey 3-yr spectroscopically confirmed cosmological sample, obtaining photometry in a series of 'local' apertures centred on the SN, and for the global host galaxy. We study the differences in these host galaxy properties, such as stellar mass and rest-frame U - R colours, and their correlations with SN Ia parameters including Hubble residuals. We find all Hubble residual steps to be >3σ in significance, both for splitting at the traditional environmental property sample median and for the step of maximum significance. For stellar mass, we find a maximal local step of 0.098 ± 0.018 mag; ∼0.03 mag greater than the largest global stellar mass step in our sample (0.070 ± 0.017 mag). When splitting at the sample median, differences between local and global U - R steps are small, both ∼0.08 mag, but are more significant than the global stellar mass step (0.057 ± 0.017 mag). We split the data into sub-samples based on SN Ia light-curve parameters: stretch (x1) and colour (c), finding that redder objects (c > 0) have larger Hubble residual steps, for both stellar mass and U - R, for both local and global measurements, of ∼0.14 mag. Additionally, the bluer (star-forming) local environments host a more homogeneous SN Ia sample, with local U - R rms scatter as low as 0.084 ± 0.017 mag for blue (c < 0) SNe Ia in locally blue U - R environments
Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey
On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star–black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10−8.56, and has a velocity between 0.18c and 0.21c are disfavored at the 2σ level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4σ level in 95% of future follow-up observations
A Search of the Full Six Years of the Dark Energy Survey for Outer Solar System Objects
We present the results of a search for outer Solar System objects in the full
six years of data (Y6) from the Dark Energy Survey (DES). The DES covered a
contiguous deg of the southern sky with deg
exposures in the optical/IR filters between 2013 and 2019. This search
yielded 815 trans-Neptunian objects (TNOs), one Centaur and one Oort cloud
comet, with 461 objects reported for the first time in this paper. We present
methodology that builds upon our previous search carried out on the first four
years of data. Here, all DES images were reprocessed with an improved detection
pipeline that leads to an average completeness gain of 0.47 mag per exposure,
as well as an improved transient catalog production and optimized algorithms
for linkage of detections into orbits. All objects were verified by visual
inspection and by computing the sub-threshold significance, the total
signal-to-noise ratio in the stack of images in which the object's presence is
indicated by the orbit fit, but no detection was reported. This yields a highly
pure catalog of TNOs complete to mag and distances
au. The Y6 TNOs have minimum (median) of 7 (12) distinct nights' detections and
arcs of 1.1 (4.2) years, and will have magnitudes available in a
further publication. We present software for simulating our observational
biases that enable comparisons of population models to our detections. Initial
inferences demonstrating the statistical power of the DES catalog are: the data
are inconsistent with the CFEPS-L7 model for the classical Kuiper Belt; the 16
``extreme'' TNOs ( au, au) are consistent with the null
hypothesis of azimuthal isotropy; and non-resonant TNOs with au,
au show a highly significant tendency to be sunward of the major mean motion
resonances, whereas this tendency is not present for au
Measurements of the Electroweak Diboson Production Cross Sections in Proton-Proton Collisions at =5.02 TeV Using Leptonic Decays
The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 302 pb. Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The WW, WZ, and ZZ total cross sections are measured as σWW=37.0(stat)(syst) pb , σWZ=6.4(stat)(syst) pb, and σZZ=5.3(stat)(syst) pb
Cosmological constraints from the tomographic cross-correlation of DESI Luminous Red Galaxies and Planck CMB lensing
We use luminous red galaxies selected from the imaging surveys that are being used for targeting by the Dark Energy Spectroscopic Instrument (DESI) in combination with CMB lensing maps from the Planck collaboration to probe the amplitude of large-scale structure over 0.4 ≤ z ≤ 1. Our galaxy sample, with an angular number density of approximately 500 deg-2 over 18,000 sq.deg., is divided into 4 tomographic bins by photometric redshift and the redshift distributions are calibrated using spectroscopy from DESI. We fit the galaxy autospectra and galaxy-convergence cross-spectra using models based on cosmological perturbation theory, restricting to large scales that are expected to be well described by such models. Within the context of ΛCDM, combining all 4 samples and using priors on the background cosmology from supernova and baryon acoustic oscillation measurements, we find S 8 = σ8(ωm/0.3)0.5 = 0.73 ± 0.03. This result is lower than the prediction of the ΛCDM model conditioned on the Planck data. Our data prefer a slower growth of structure at low redshift than the model predictions, though at only modest significance
The PAU Survey: narrowband photometric redshifts using Gaussian processes
We study the performance of the hybrid template-machine-learning photometric
redshift (photo-) algorithm Delight, which uses Gaussian processes, on a
subset of the early data release of the Physics of the Accelerating Universe
Survey (PAUS). We calibrate the fluxes of the PAUS narrow bands with
broadband fluxes () in the COSMOS field using three different methods,
including a new method which utilises the correlation between the apparent size
and overall flux of the galaxy. We use a rich set of empirically derived galaxy
spectral templates as guides to train the Gaussian process, and we show that
our results are competitive with other standard photometric redshift
algorithms. Delight achieves a photo- th percentile error of
without any quality cut for galaxies with
as compared to and for the
BPz and ANNz2 codes, respectively. Delight is also shown to produce more
accurate probability distribution functions for individual redshift estimates
than BPz and ANNz2. Common photo- outliers of Delight and BCNz2 (previously
applied to PAUS) are found to be primarily caused by outliers in the narrowband
fluxes, with a small number of cases potentially indicating spectroscopic
redshift failures in the reference sample. In the process, we introduce
performance metrics derived from the results of BCNz2 and Delight, allowing us
to achieve a photo- quality of at a magnitude of
while keeping per cent objects of the galaxy
sample.Comment: 19 pages, 16 figures, accepted by MNRA
Search for magnetically-induced signatures in the arrival directions of ultra-high-energy cosmic rays measured at the Pierre Auger Observatory
We search for signals of magnetically-induced effects in the arrival directions of ultra-high-energy cosmic rays detected at the Pierre Auger Observatory. We apply two different methods. One is a search for sets of events that show a correlation between their arrival direction and the inverse of their energy, which would be expected if they come from the same point-like source, they have the same electric charge and their deflection is relatively small and coherent. We refer to these sets of events as "multiplets". The second method, called "thrust", is a principal axis analysis aimed to detect the elongated patterns in a region of interest. We study the sensitivity of both methods using a benchmark simulation and we apply them to data in two different searches. The first search is done assuming as source candidates a list of nearby active galactic nuclei and starburst galaxies. The second is an all-sky blind search. We report the results and we find no statistically significant features. We discuss the compatibility of these results with the indications on the mass composition inferred from data of the Pierre Auger Observatory. © 2020 IOP Publishing Ltd and Sissa Medialab
Measurements of the Electroweak Diboson Production Cross Sections in Proton-Proton Collisions at s=5.02 TeV Using Leptonic Decays
Copyright © 2021 CERN, for the CMS Collaboration. The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 302 pb−1. Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The WW, WZ, and ZZ total cross sections are measured as σWW = 37:0 +5.5 −5.2 (stat) +2.7 −2.6(syst) pb, σWZ = 6.4 +2.5 −2.1 (stat) +0.5 −0.3 (syst) pb, and σZZ = 5.3 +2.5 −2.1(stat) +0.5 −0.4 (syst) pb. All measurements are in good agreement with theoretical calculations at combined next-to-next-to-leading order quantum chromodynamics and next-to-leading order electroweak accuracy.SCOAP3