38 research outputs found
A search for faint resolved galaxies beyond the Milky Way in DES Year 6: A new faint, diffuse dwarf satellite of NGC 55
We report results from a systematic wide-area search for faint dwarf galaxies
at heliocentric distances from 0.3 to 2 Mpc using the full six years of data
from the Dark Energy Survey (DES). Unlike previous searches over the DES data,
this search specifically targeted a field population of faint galaxies located
beyond the Milky Way virial radius. We derive our detection efficiency for
faint, resolved dwarf galaxies in the Local Volume with a set of synthetic
galaxies and expect our search to be complete to ~ mag for
galaxies at Mpc respectively. We find no new field dwarfs in
the DES footprint, but we report the discovery of one high-significance
candidate dwarf galaxy at a distance of Mpc, a
potential satellite of the Local Volume galaxy NGC 55, separated by arcmin
(physical separation as small as 30 kpc). We estimate this dwarf galaxy to have
an absolute V-band magnitude of mag and an
azimuthally averaged physical half-light radius of
kpc, making this one of the lowest surface brightness galaxies ever found with
mag . This is the largest, most diffuse galaxy
known at this luminosity, suggesting possible tidal interactions with its host.Comment: 20 pages, 7 figure
Synchronous Rotation in the (136199) ErisâDysnomia System
We combine photometry of Eris from a 6 month campaign on the Palomar 60 inch telescope in 2015, a 1 month Hubble Space Telescope WFC3 campaign in 2018, and Dark Energy Survey data spanning 2013â2018 to determine a light curve of definitive period 15.771 ± 0.008 days (1Ï formal uncertainties), with nearly sinusoidal shape and peak-to-peak flux variation of 3%. This is consistent at part-per-thousand precision with the P = 15.785 90 ± 0.00005 day sidereal period of Dysnomia's orbit around Eris, strengthening the recent detection of synchronous rotation of Eris by SzakĂĄts et al. with independent data. Photometry from Gaia are consistent with the same light curve. We detect a slope of 0.05 ± 0.01 mag per degree of Eris's brightness with respect to illumination phase averaged across g, V, and r bands, intermediate between Pluto's and Charon's values. Variations of 0.3 mag are detected in Dysnomia's brightness, plausibly consistent with a double-peaked light curve at the synchronous period. The synchronous rotation of Eris is consistent with simple tidal models initiated with a giant-impact origin of the binary, but is difficult to reconcile with gravitational capture of Dysnomia by Eris. The high albedo contrast between Eris and Dysnomia remains unexplained in the giant-impact scenario
The Dark Energy Survey Supernova Program: Cosmological Biases from Host Galaxy Mismatch of Type Ia Supernovae
Redshift measurements, primarily obtained from host galaxies, are essential
for inferring cosmological parameters from type Ia supernovae (SNe Ia).
Matching SNe to host galaxies using images is non-trivial, resulting in a
subset of SNe with mismatched hosts and thus incorrect redshifts. We evaluate
the host galaxy mismatch rate and resulting biases on cosmological parameters
from simulations modeled after the Dark Energy Survey 5-Year (DES-SN5YR)
photometric sample. For both DES-SN5YR data and simulations, we employ the
directional light radius method for host galaxy matching. In our SN Ia
simulations, we find that 1.7% of SNe are matched to the wrong host galaxy,
with redshift difference between the true and matched host of up to 0.6. Using
our analysis pipeline, we determine the shift in the dark energy equation of
state parameter (Dw) due to including SNe with incorrect host galaxy matches.
For SN Ia-only simulations, we find Dw = 0.0013 +/- 0.0026 with constraints
from the cosmic microwave background (CMB). Including core-collapse SNe and
peculiar SNe Ia in the simulation, we find that Dw ranges from 0.0009 to 0.0032
depending on the photometric classifier used. This bias is an order of
magnitude smaller than the expected total uncertainty on w from the DES-SN5YR
sample of around 0.03. We conclude that the bias on w from host galaxy mismatch
is much smaller than the uncertainties expected from the DES-SN5YR sample, but
we encourage further studies to reduce this bias through better host-matching
algorithms or selection cuts.Comment: Accepted by Ap
Characterizing the intracluster light over the redshift range 0.2 < z < 0.8 in the DES-ACT overlap
We characterize the properties and evolution of bright central galaxies (BCGs) and the surrounding intracluster light (ICL) in galaxy clusters identified in the Dark Energy Survey and Atacama Cosmology Telescope Survey (DES-ACT) overlapping regions, covering the redshift range 0.20 14.4. We also measure the stellar massâhalo mass (SMHM) relation for the BCG+ICL system and find that the slope, ÎČ, which characterizes the dependence of M200m,SZ on the BCG+ICL stellar mass, increases with radius. The outskirts are more strongly correlated with the halo than the core, which supports that the BCG+ICL system follows a two-phase growth, where recent growth (z < 2) occurs beyond the BCGâs core. Additionally, we compare our observed SMHM relation results to the IllustrisTNG300-1 cosmological hydrodynamic simulations and find moderate qualitative agreement in the amount of diffuse light. However, the SMHM relationâs slope is steeper in TNG300-1 and the intrinsic scatter is lower, likely from the absence of projection effects in TNG300-1. Additionally, we find that the ICL exhibits a colour gradient such that the outskirts are bluer than the core. Moreover, for the lower halo mass clusters (log10(M200m,SZ/Mâ) < 14.59), we detect a modest change in the colour gradientâs slope with lookback time, which combined with the absence of stellar mass growth may suggest that lower mass clusters have been involved in growth via tidal stripping more recently than their higher mass counterparts
Lensing Without Borders. I. A Blind Comparison of the Amplitude of Galaxy-Galaxy Lensing Between Independent Imaging Surveys
Lensing Without Borders is a cross-survey collaboration created to assess the
consistency of galaxy-galaxy lensing signals () across different
data-sets and to carry out end-to-end tests of systematic errors. We perform a
blind comparison of the amplitude of using lens samples from
BOSS and six independent lensing surveys. We find good agreement between
empirically estimated and reported systematic errors which agree to better than
2.3 in four lens bins and three radial ranges. For lenses with and considering statistical errors, we detect a 3-4
correlation between lensing amplitude and survey depth. This correlation could
arise from the increasing impact at higher redshift of unrecognised galaxy
blends on shear calibration and imperfections in photometric redshift
calibration. At amplitudes may additionally correlate with
foreground stellar density. The amplitude of these trends is within
survey-defined systematic error budgets which are designed to include known
shear and redshift calibration uncertainty. Using a fully empirical and
conservative method, we do not find evidence for large unknown systematics.
Systematic errors greater than 15% (25%) ruled out in three lens bins at 68%
(95%) confidence at . Differences with respect to predictions based on
clustering are observed to be at the 20-30% level. Our results therefore
suggest that lensing systematics alone are unlikely to fully explain the
"lensing is low" effect at . This analysis demonstrates the power of
cross-survey comparisons and provides a promising path for identifying and
reducing systematics in future lensing analyses.Comment: 41 page, 20 figure
Dark Energy Survey Year 3 Results: Galaxy mock catalogs for BAO analysis
The calibration and validation of scientific analysis in simulations is a fundamental tool to ensure unbiased and robust results in observational cosmology. In particular, mock galaxy catalogs are a crucial resource to achieve these goals in the measurement of baryon acoustic oscillation (BAO) in the clustering of galaxies. Here we present a set of 1952 galaxy mock catalogs designed to mimic the Dark Energy Survey Year 3 BAO sample over its full photometric redshift range 0.6â<âzphotoâ<â1.1. The mocks are based upon 488 ICE-COLA fast N-body simulations of full-sky light cones and were created by populating halos with galaxies, using a hybrid halo occupation distribution â halo abundance matching model. This model has ten free parameters, which were determined, for the first time, using an automatic likelihood minimization procedure. We also introduced a novel technique to assign photometric redshift for simulated galaxies, following a two-dimensional probability distribution with VIMOS Public Extragalactic Redshift Survey data. The calibration was designed to match the observed abundance of galaxies as a function of photometric redshift, the distribution of photometric redshift errors, and the clustering amplitude on scales smaller than those used for BAO measurements. An exhaustive analysis was done to ensure that the mocks reproduce the input properties. Finally, mocks were tested by comparing the angular correlation function w(Ξ), angular power spectrum Câ, and projected clustering Οp(râ„) to theoretical predictions and data. The impact of volume replication in the estimate of the covariance is also investigated. The success in accurately reproducing the photometric redshift uncertainties and the galaxy clustering as a function of redshift render this mock creation pipeline as a benchmark for future analyses of photometric galaxy surveys
Cosmological shocks around galaxy clusters: A coherent investigation with DES, SPT & ACT
We search for signatures of cosmological shocks in gas pressure profiles of
galaxy clusters using the cluster catalogs from three surveys: the Dark Energy
Survey (DES) Year 3, the South Pole Telescope (SPT) SZ survey, and the Atacama
Cosmology Telescope (ACT) data releases 4, 5, and 6, and using thermal
Sunyaev-Zeldovich (SZ) maps from SPT and ACT. The combined cluster sample
contains around clusters with mass and redshift ranges and , and the total sky coverage
of the maps is . We find a clear pressure
deficit at in SZ profiles around both ACT and SPT
clusters, estimated at significance, which is qualitatively
consistent with a shock-induced thermal non-equilibrium between electrons and
ions. The feature is not as clearly determined in profiles around DES clusters.
We verify that measurements using SPT or ACT maps are consistent across all
scales, including in the deficit feature. The SZ profiles of optically selected
and SZ-selected clusters are also consistent for higher mass clusters. Those of
less massive, optically selected clusters are suppressed on small scales by
factors of 2-5 compared to predictions, and we discuss possible interpretations
of this behavior. An oriented stacking of clusters -- where the orientation is
inferred from the SZ image, the brightest cluster galaxy, or the surrounding
large-scale structure measured using galaxy catalogs -- shows the normalization
of the one-halo and two-halo terms vary with orientation. Finally, the location
of the pressure deficit feature is statistically consistent with existing
estimates of the splashback radius.Comment: [v2]: Version accepted to MNRA
OzDES Reverberation Mapping Program: H beta lags from the 6-yr survey
Reverberation mapping measurements have been used to constrain the relationship between the size of the broad-line region and luminosity of active galactic nuclei (AGN). This RâL relation is used to estimate single-epoch virial black hole masses, and has been proposed to use to standardize AGN to determine cosmological distances. We present reverberation measurements made with HÎČ from the 6-yr Australian Dark Energy Survey (OzDES) Reverberation Mapping Program. We successfully recover reverberation lags for eight AGN at 0.12 &lt; z &lt; 0.71, probing higher redshifts than the bulk of HÎČ measurements made to date. Our fit to the RâL relation has a slope of α = 0.41 ± 0.03 and an intrinsic scatter of Ï = 0.23 ± 0.02âdex. The results from our multi-object spectroscopic survey are consistent with previous measurements made by dedicated source-by-source campaigns, and with the observed dependence on accretion rate. Future surveys, including LSST, TiDES, and SDSS-V, which will be revisiting some of our observed fields, will be able to build on the results of our first-generation multi-object reverberation mapping survey
Multiwavelength optical and NIR variability analysis of the Blazar PKS 0027-426
We present multiwavelength spectral and temporal variability analysis of PKS 0027-426 using optical griz observations from Dark Energy Survey between 2013 and 2018 and VEILS Optical Light curves of Extragalactic TransienT Events (VOILETTE) between 2018 and 2019 and near-infrared (NIR) JKs observations from Visible and Infrared Survey Telescope for Astronomy Extragalactic Infrared Legacy Survey (VEILS) between 2017 and 2019. Multiple methods of cross-correlation of each combination of light curve provides measurements of possible lags between opticalâoptical, opticalâNIR, and NIRâNIR emission, for each observation season and for the entire observational period. Inter-band time lag measurements consistently suggest either simultaneous emission or delays between emission regions on time-scales smaller than the cadences of observations. The colourâmagnitude relation between each combination of filters was also studied to determine the spectral behaviour of PKS 0027-426. Our results demonstrate complex colour behaviour that changes between bluer when brighter, stable when brighter, and redder when brighter trends over different time-scales and using different combinations of optical filters. Additional analysis of the optical spectra is performed to provide further understanding of this complex spectral behaviour
Dark Energy Survey Year 3 results: marginalization over redshift distribution uncertainties using ranking of discrete realizations
Cosmological information from weak lensing surveys is maximized by sorting source galaxies into tomographic redshift subsamples. Any uncertainties on these redshift distributions must be correctly propagated into the cosmological results. We present hyperrank, a new method for marginalizing over redshift distribution uncertainties, using discrete samples from the space of all possible redshift distributions, improving over simple parametrized models. In hyperrank, the set of proposed redshift distributions is ranked according to a small (between one and four) number of summary values, which are then sampled, along with other nuisance parameters and cosmological parameters in the Monte Carlo chain used for inference. This approach can be regarded as a general method for marginalizing over discrete realizations of data vector variation with nuisance parameters, which can consequently be sampled separately from the main parameters of interest, allowing for increased computational efficiency. We focus on the case of weak lensing cosmic shear analyses and demonstrate our method using simulations made for the Dark Energy Survey (DES). We show that the method can correctly and efficiently marginalize over a wide range of models for the redshift distribution uncertainty. Finally, we compare hyperrank to the common mean-shifting method of marginalizing over redshift uncertainty, validating that this simpler model is sufficient for use in the DES Year 3 cosmology results presented in companion papers