We present the luminosity functions and host galaxy properties of the Dark Energy Survey (DES) core-collapse supernova (CCSN) sample, consisting of 69 Type II and 50 Type Ibc spectroscopically and ...photometrically-confirmed supernovae over a redshift range \(0.045<z<0.25\). We fit the observed DES \(griz\) CCSN light-curves and K-correct to produce rest-frame \(R\)-band light curves. We compare the sample with lower-redshift CCSN samples from Zwicky Transient Facility (ZTF) and Lick Observatory Supernova Search (LOSS). Comparing luminosity functions, the DES and ZTF samples of SNe II are brighter than that of LOSS with significances of 3.0\(\sigma\) and 2.5\(\sigma\) respectively. While this difference could be caused by redshift evolution in the luminosity function, simpler explanations such as differing levels of host extinction remain a possibility. We find that the host galaxies of SNe II in DES are on average bluer than in ZTF, despite having consistent stellar mass distributions. We consider a number of possibilities to explain this -- including galaxy evolution with redshift, selection biases in either the DES or ZTF samples, and systematic differences due to the different photometric bands available -- but find that none can easily reconcile the differences in host colour between the two samples and thus its cause remains uncertain.
Recent cosmological analyses with large-scale structure and weak lensing measurements, usually referred to as 3\(\times\)2pt, had to discard a lot of signal-to-noise from small scales due to our ...inability to accurately model non-linearities and baryonic effects. Galaxy-galaxy lensing, or the position-shear correlation between lens and source galaxies, is one of the three two-point correlation functions that are included in such analyses, usually estimated with the mean tangential shear. However, tangential shear measurements at a given angular scale \(\theta\) or physical scale \(R\) carry information from all scales below that, forcing the scale cuts applied in real data to be significantly larger than the scale at which theoretical uncertainties become problematic. Recently there have been a few independent efforts that aim to mitigate the non-locality of the galaxy-galaxy lensing signal. Here we perform a comparison of the different methods, including the Y-transformation, the Point-Mass marginalization methodology and the Annular Differential Surface Density statistic. We do the comparison at the cosmological constraints level in a combined galaxy clustering and galaxy-galaxy lensing analysis. We find that all the estimators yield equivalent cosmological results assuming a simulated Rubin Observatory Legacy Survey of Space and Time (LSST) Year 1 like setup and also when applied to DES Y3 data. With the LSST Y1 setup, we find that the mitigation schemes yield \(\sim\)1.3 times more constraining \(S_8\) results than applying larger scale cuts without using any mitigation scheme.
This Technical Note presents a catalog of calibrated reference stars that was generated by the Forward Calibration Method (FGCM) pipeline (arXiv:1706.01542) as part of the FGCM photometric ...calibration of the full Dark Energy Survey (DES) 6-Year data set (Y6). This catalog provides DES grizY magnitudes for 17 million stars with i-band magnitudes mostly in the range 16 < i < 21 spread over the full DES footprint covering 5000 square degrees over the Southern Galactic Cap at galactic latitudes b < -20 degrees (plus a few outlying fields disconnected from the main survey footprint). These stars are calibrated to a uniformity of better than 1.8 milli-mag (0.18%) RMS over the survey area. The absolute calibration of the catalog is computed with reference to the STISNIC.007 spectrum of the Hubble Space Telescope CalSpec standard star C26202; including systematic errors, the absolute flux system is known at the approximately 1% level. As such, these stars provide a useful reference catalog for calibrating grizY-band or grizY-like band photometry in the Southern Hemisphere, particularly for observations within the DES footprint.
We infer the mean optical depth of a sample of optically-selected galaxy clusters from the Dark Energy Survey (DES) via the pairwise kinematic Sunyaev-Zel'dovich (kSZ) effect. The pairwise kSZ signal ...between pairs of clusters drawn from the DES Year-3 cluster catalog is detected at \(4.1 \sigma\) in cosmic microwave background (CMB) temperature maps from two years of observations with the SPT-3G camera on the South Pole Telescope. After cuts, there are 24,580 clusters in the \(\sim 1,400\) deg\(^2\) of the southern sky observed by both experiments. We infer the mean optical depth of the cluster sample with two techniques. The optical depth inferred from the pairwise kSZ signal is \(\bar{\tau}_e = (2.97 \pm 0.73) \times 10^{-3}\), while that inferred from the thermal SZ signal is \(\bar{\tau}_e = (2.51 \pm 0.55^{\text{stat}} \pm 0.15^{\rm syst}) \times 10^{-3}\). The two measures agree at \(0.6 \sigma\). We perform a suite of systematic checks to test the robustness of the analysis.
The fiducial cosmological analyses of imaging galaxy surveys like the Dark
Energy Survey (DES) typically probe the Universe at redshifts $z < 1$. This is
mainly because of the limited depth of these ...surveys, and also because such
analyses rely heavily on galaxy lensing, which is more efficient at low
redshifts. In this work we present the selection and characterization of
high-redshift galaxy samples using DES Year 3 data, and the analysis of their
galaxy clustering measurements. In particular, we use galaxies that are fainter
than those used in the previous DES Year 3 analyses and a Bayesian redshift
scheme to define three tomographic bins with mean redshifts around $z \sim
0.9$, $1.2$ and $1.5$, which significantly extend the redshift coverage of the
fiducial DES Year 3 analysis. These samples contain a total of about 9 million
galaxies, and their galaxy density is more than 2 times higher than those in
the DES Year 3 fiducial case. We characterize the redshift uncertainties of the
samples, including the usage of various spectroscopic and high-quality redshift
samples, and we develop a machine-learning method to correct for correlations
between galaxy density and survey observing conditions. The analysis of galaxy
clustering measurements, with a total signal-to-noise $S/N \sim 70$ after scale
cuts, yields robust cosmological constraints on a combination of the fraction
of matter in the Universe $\Omega_m$ and the Hubble parameter $h$, $\Omega_m h
= 0.195^{+0.023}_{-0.018}$, and 2-3% measurements of the amplitude of the
galaxy clustering signals, probing galaxy bias and the amplitude of matter
fluctuations, $b \sigma_8$. A companion paper $\textit{(in preparation)}$ will
present the cross-correlations of these high-$z$ samples with CMB lensing from
Planck and SPT, and the cosmological analysis of those measurements in
combination with the galaxy clustering presented in this work.
We perform a search for galaxy-galaxy strong lens systems using a convolutional neural network (CNN) applied to imaging data from the first public data release of the DECam Local Volume Exploration ...Survey (DELVE), which contains \(\sim 520\) million astronomical sources covering \(\sim 4,000\) \(\mathrm{deg}^2\) of the southern sky to a \(5\sigma\) point-source depth of \(g=24.3\), \(r=23.9\), \(i=23.3\), and \(z=22.8\) mag. Following the methodology of similar searches using DECam data, we apply color and magnitude cuts to select a catalog of \(\sim 11\) million extended astronomical sources. After scoring with our CNN, the highest scoring 50,000 images were visually inspected and assigned a score on a scale from 0 (definitely not a lens) to 3 (very probable lens). We present a list of 617 strong lens candidates, 599 of which are previously unreported. We categorize our candidates using their human-assigned scores, resulting in 60 Grade A candidates, 160 Grade B candidates, and 397 Grade C candidates. We additionally highlight 8 potential quadruply lensed quasars from this sample. Due to the location of our search footprint in the northern Galactic cap (\(b > 10\) deg) and southern celestial hemisphere (\({\rm Dec.}<0\) deg), our candidate list has little overlap with other existing ground-based searches. Where our search footprint does overlap with other searches, we find a significant number of high-quality candidates which were previously unidentified, indicating a degree of orthogonality in our methodology. We report properties of our candidates including apparent magnitude and Einstein radius estimated from the image separation.
We report the methods of and initial scientific inferences from the extraction of precision photometric information for the \(>800\) trans-Neptunian objects (TNOs) discovered in the images of the ...Dark Energy Survey (DES). Scene-modelling photometry is used to obtain shot-noise-limited flux measures for each exposure of each TNO, with background sources subtracted. Comparison of double-source fits to the pixel data with single-source fits are used to identify and characterize two binary TNO systems. A Markov Chain Monte Carlo method samples the joint likelihood of the intrinsic colors of each source as well as the amplitude of its flux variation, given the time series of multiband flux measurements and their uncertainties. A catalog of these colors and light curve amplitudes \(A\) is included with this publication. We show how to assign a likelihood to the distribution \(q(A)\) of light curve amplitudes in any subpopulation. Using this method, we find decisive evidence (i.e. evidence ratio \(<0.01\)) that cold classical (CC) TNOs with absolute magnitude \(6<H_r<8.2\) are more variable than the hot classical (HC) population of the same \(H_r\), reinforcing theories that the former form in situ and the latter arise from a different physical population. Resonant and scattering TNOs in this \(H_r\) range have variability consistent with either the HC's or CC's. DES TNOs with \(H_r<6\) are seen to be decisively less variable than higher-\(H_r\) members of any dynamical group, as expected. More surprising is that detached TNOs are decisively less variable than scattering TNOs, which requires them to have distinct source regions or some subsequent differential processing.
We present a sample of 19,583 ultracool dwarf candidates brighter than z \(\leq 23\) selected from the Dark Energy Survey DR2 coadd data matched to VHS DR6, VIKING DR5 and AllWISE covering \(\sim\) ...4,800 \(deg^2\). The ultracool candidates were first pre-selected based on their (i-z), (z-Y), and (Y-J) colours. They were further classified using a method that compares their optical, near-infrared and mid-infrared colours against templates of M, L and T dwarfs. 14,099 objects are presented as new L and T candidates and the remaining objects are from the literature, including 5,342 candidates from our previous work. Using this new and deeper sample of ultracool dwarf candidates we also present: 20 new candidate members to nearby young moving groups (YMG) and associations, variable candidate sources and four new wide binary systems composed of two ultracool dwarfs. Finally, we also show the spectra of twelve new ultracool dwarfs discovered by our group and presented here for the first time. These spectroscopically confirmed objects are a sanity check of our selection of ultracool dwarfs and photometric classification method.
We present a method for mapping variations between probability distribution functions and apply this method within the context of measuring galaxy redshift distributions from imaging survey data. ...This method, which we name PITPZ for the probability integral transformations it relies on, uses a difference in curves between distribution functions in an ensemble as a transformation to apply to another distribution function, thus transferring the variation in the ensemble to the latter distribution function. This procedure is broadly applicable to the problem of uncertainty propagation. In the context of redshift distributions, for example, the uncertainty contribution due to certain effects can be studied effectively only in simulations, thus necessitating a transfer of variation measured in simulations to the redshift distributions measured from data. We illustrate the use of PITPZ by using the method to propagate photometric calibration uncertainty to redshift distributions of the Dark Energy Survey Year 3 weak lensing source galaxies. For this test case, we find that PITPZ yields a lensing amplitude uncertainty estimate due to photometric calibration error within 1 per cent of the truth, compared to as much as a 30 per cent underestimate when using traditional methods.
Two of the most sensitive probes of the large scale structure of the universe are the clustering of galaxies and the tangential shear of background galaxy shapes produced by those foreground ...galaxies, so-called galaxy-galaxy lensing. Combining the measurements of these two two-point functions leads to cosmological constraints that are independent of the galaxy bias factor. The optimal choice of foreground, or lens, galaxies is governed by the joint, but conflicting requirements to obtain accurate redshift information and large statistics. We present cosmological results from the full 5000 sq. deg. of the Dark Energy Survey first three years of observations (Y3) combining those two-point functions, using for the first time a magnitude-limited lens sample (MagLim) of 11 million galaxies especially selected to optimize such combination, and 100 million background shapes. We consider two cosmological models, flat \(\Lambda\)CDM and \(w\)CDM. In \(\Lambda\)CDM we obtain for the matter density \(\Omega_m = 0.320^{+0.041}_{-0.034}\) and for the clustering amplitude \(S_8 = 0.778^{+0.037}_{-0.031}\), at 68% C.L. The latter is only 1\(\sigma\) smaller than the prediction in this model informed by measurements of the cosmic microwave background by the Planck satellite. In \(w\)CDM we find \(\Omega_m = 0.32^{+0.044}_{-0.046}\), \(S_8=0.777^{+0.049}_{-0.051}\), and dark energy equation of state \(w=-1.031^{+0.218}_{-0.379}\). We find that including smaller scales while marginalizing over non-linear galaxy bias improves the constraining power in the \(\Omega_m-S_8\) plane by \(31\)% and in the \(\Omega_m-w\) plane by \(41\)% while yielding consistent cosmological parameters from those in the linear bias case. These results are combined with those from cosmic shear in a companion paper to present full DES-Y3 constraints from the three two-point functions (3x2pt).
