Transfer learning for galaxy morphology from one survey to another

© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Deep Learning (DL) algorithms for morphological classification of galaxies have proven very successful, mimicking (or even improving) visual classifications. However, these algorithms rely on large training samples of labelled galaxies (typically thousands of them). A key question for using DL classifications in future Big Data surveys is how much of the knowledge acquired from an existing survey can be exported to a new dataset, i.e. if the features learned by the machines are meaningful for different data. We test the performance of DL models, trained with Sloan Digital Sky Survey (SDSS) data, on Dark Energy survey (DES) using images for a sample of $\sim$5000 galaxies with a similar redshift distribution to SDSS. Applying the models directly to DES data provides a reasonable global accuracy ($\sim$ 90%), but small completeness and purity values. A fast domain adaptation step, consisting in a further training with a small DES sample of galaxies ($\sim$500-300), is enough for obtaining an accuracy > 95% and a significant improvement in the completeness and purity values. This demonstrates that, once trained with a particular dataset, machines can quickly adapt to new instrument characteristics (e.g., PSF, seeing, depth), reducing by almost one order of magnitude the necessary training sample for morphological classification. Redshift evolution effects or significant depth differences are not taken into account in this study.Peer reviewedFinal Accepted Versio

Structure of high-spin states in 91Sr and 92Sr

The nuclei 91Sr and 92Sr were produced at high spin as fission fragments following the fusion reaction 36S+ 159Tb at 165 MeV. γ rays were detected with the Gammasphere array. The level schemes of 91Sr and 92Sr were extended up to E≈6 MeV and E≈8 MeV, respectively. Level structures in 91Sr and 92Sr were interpreted in shell-model calculations performed in the configuration space (0f5/2, 1p3/2, 1p1/2, 0g9/2) for the protons and (1p1/2, 0g9/2, 1d5/2) for the neutrons. Negative-parity states in the yrast sequences are described in these calculations by coupling 3- proton excitations to the unpaired 1d5/2 neutrons. A possible reduction of the gap between the proton 1p3/2 and 1p1/2 orbitals in 92Sr is discussed

Superluminous supernovae from the Dark Energy Survey

We present a sample of 21 hydrogen-free superluminous supernovae (SLSNe-I) and one hydrogen-rich SLSN (SLSN-II) detected during the five-year Dark Energy Survey (DES). These SNe, located in the redshift range 0.220 < z < 1.998, represent the largest homogeneously selected sample of SLSN events at high redshift. We present the observed g, r, i, z light curves for these SNe, which we interpolate using Gaussian processes. The resulting light curves are analysed to determine the luminosity function of SLSNe-I, and their evolutionary timescales. The DES SLSN-I sample significantly broadens the distribution of SLSN-I light-curve properties when combined with existing samples from the literature. We fit a magnetar model to our SLSNe, and find that this model alone is unable to replicate the behaviour of many of the bolometric light curves. We search the DES SLSN-I light curves for the presence of initial peaks prior to the main light-curve peak. Using a shock breakout model, our Monte Carlo search finds that 3 of our 14 events with pre-max data display such initial peaks. However, 10 events show no evidence for such peaks, in some cases down to an absolute magnitude of<−16, suggesting that such features are not ubiquitous to all SLSN-I events. We also identify a red pre-peak feature within the light curve of one SLSN, which is comparable to that observed within SN2018bsz

First cosmology results using SNe Ia from the dark energy survey: analysis, systematic uncertainties, and validation

International audienceWe present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified type Ia supernovae (SNe Ia) from the first three years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.01

False Beliefs About Asylum Seekers to Australia: The Role of Confidence in Such Beliefs, Prejudice, and the Third Person Effect

There has been much controversy about the treatment of asylum seekers in Australia in recent years, with the Australian Government continuing to enforce a very hard-line stance on asylum seekers who arrive to Australia by boat. The present study examined attitudes towards asylum seekers using 164 Australian community members during June 2015 by way of questionnaire. Our primary research question involved how five variables predicted false beliefs about asylum seekers. Specifically, we measured prejudice, the third-person effect, and confidence in the answers given to false beliefs about asylum seekers. Regression results indicated that the main predictors of false beliefs were right-wing political orientation, prejudice, confidence in espousing false beliefs, and the third-person effect (politicians). Furthermore, most of our community participants accepted a large number of false beliefs as being true, with approximately two-thirds of our participants scoring above the midpoint. This reflects similar findings over the last decade or so. Our results indicate that, if one believes in bottom-up change, a more nuanced approach needs to be undertaken with community anti-prejudice interventions

In-beam γ-ray spectroscopy of 172Pt

Collective structures in 172Pt have been investigated by measuring in-beam γ rays with mass selection and the recoil-decay tagging technique. The discrepancy in the ground-state band from previous studies has been resolved, and a new collective structure that is likely based on an octupole vibration has been identified. A band mixing model is used to determine the properties of the competing near-spherical and deformed ground-state sequences in the light Os-Pt-Hg-Pb region. Evidence for a reduction of deformation in the deformed vacuum structure below N=98 is presented

First cosmology results using type Ia supernovae from the Dark Energy Survey: constraints on cosmological parameters

We present the first cosmological parameter constraints using measurements of type Ia supernovae (SNe Ia) from the Dark Energy Survey Supernova Program (DES-SN). The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first three years of DES-SN, combined with a low-redshift sample of 122 SNe from the literature. Our "DES-SN3YR" result from these 329 SNe Ia is based on a series of companion analyses and improvements covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties. For a flat LCDM model we find a matter density Omega_m = 0.331 +_ 0.038. For a flat wCDM model, and combining our SN Ia constraints with those from the cosmic microwave background (CMB), we find a dark energy equation of state w = -0.978 +_ 0.059, and Omega_m = 0.321 +_ 0.018. For a flat w0waCDM model, and combining probes from SN Ia, CMB and baryon acoustic oscillations, we find w0 = -0.885 +_ 0.114 and wa = -0.387 +_ 0.430. These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA)

Measurement of the splashback feature around SZ-selected Galaxy clusters with DES, SPT, and ACT

We present a detection of the splashback feature around galaxy clusters selected using the Sunyaev–Zel’dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, rsp, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that rsp inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these cluster samples with galaxies detected in the Dark Energy Survey Year 3 data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases, potentially ameliorating causes of systematic error for optically selected clusters. We find that the measured rsp for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected redMaPPer clusters with similar mass and redshift distributions, rsp is ∼2σ smaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogues and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy colour, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster

K-hindered decay of a six-quasiparticle isomer in Hf176

The structure and decay properties of high-K isomers in Hf176 have been studied using beam sweeping techniques and the Gammasphere multidetector array. A new ΔK=8 decay branch, from a Kπ=22⊃-, six-quasiparticle, isomeric (t1/2=43μs) state at 4864 keV to the 20⊃- state of a Kπ=14⊃- band, has been identified. The reduced hindrance factor per degree of K forbiddenness for this decay is measured to be unusually low (fν=3.2), which suggests K mixing in the states involved. The deduced interaction matrix elements are discussed within the context of relevant K-mixing scenarios. The 3266-keV state, previously interpreted as a Kπ=16⊃+ intrinsic state, is reassigned as the Jπ=16⊃+ member of the band based on the Kπ=15⊃+ state at 3080 keV. The systematics of fν values as a function of the degree of forbiddenness is discussed in light of this change

DES Y3 + KiDS-1000: Consistent cosmology combining cosmic shear surveys

We present a joint cosmic shear analysis of the Dark Energy Survey (DES Y3) and the Kilo-Degree Survey (KiDS-1000) in a collaborative effort between the two survey teams. We find consistent cosmological parameter constraints between DES Y3 and KiDS-1000 which, when combined in a joint-survey analysis, constrain the parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ with a mean value of $0.790^{+0.018}_{-0.014}$. The mean marginal is lower than the maximum a posteriori estimate, $S_8=0.801$, owing to skewness in the marginal distribution and projection effects in the multi-dimensional parameter space. Our results are consistent with $S_8$ constraints from observations of the cosmic microwave background by Planck, with agreement at the $1.7\sigma$ level. We use a Hybrid analysis pipeline, defined from a mock survey study quantifying the impact of the different analysis choices originally adopted by each survey team. We review intrinsic alignment models, baryon feedback mitigation strategies, priors, samplers and models of the non-linear matter power spectrum.Comment: 38 pages, 21 figures, 15 tables, submitted to the Open Journal of Astrophysics. Watch the core team discuss this analysis at https://cosmologytalks.com/2023/05/26/des-kid