arXiv subjects

S. R. Hinton

Publications and source records attributed to S. R. Hinton.

At least 217 records · Page 12Linked to original sources

arXiv2020

Machine Learning for Searching the Dark Energy Survey for Trans-Neptunian Objects

In this paper we investigate how implementing machine learning could improve the efficiency of the search for Trans-Neptunian Objects (TNOs) within Dark Energy Survey (DES) data when used alongside orbit fitting. The discovery of multiple TNOs that appear to show a similarity in their orbital parameters has led to the suggestion that one or more undetected planets, an as yet undiscovered "Planet 9", may be present in the outer Solar System. DES is well placed to detect such a planet and has already been used to discover many other TNOs. Here, we perform tests on eight different supervised machine learning algorithms, using a dataset consisting of simulated TNOs buried within real DES noise data. We found that the best performing classifier was the Random Forest which, when optimised, performed well at detecting the rare objects. We achieve an area under the receiver operating characteristic (ROC) curve, (AUC) $= 0.996 \pm 0.001$. After optimizing the decision threshold of the Random Forest, we achieve a recall of 0.96 while maintaining a precision of 0.80. Finally, by using the optimized classifier to pre-select objects, we are able to run the orbit-fitting stage of our detection pipeline five times faster.

astro-ph.EP↗

arXiv2020

The Atacama Cosmology Telescope: A Catalog of > 4000 Sunyaev-Zel'dovich Galaxy Clusters

We present a catalog of 4195 optically confirmed Sunyaev-Zel'dovich (SZ) selected galaxy clusters detected with signal-to-noise > 4 in 13,211 deg$^2$ of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multi-frequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008-2018, and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 < z < 1.91 (median z = 0.52). The catalog contains 222 z > 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ-signal vs. mass scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M500c > 3.8 x 10$^{14}$ MSun, evaluated at z = 0.5, for clusters detected at signal-to-noise ratio > 5 in maps filtered at an angular scale of 2.4'. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ-signal mass-scaling relation, such as the Dark Energy Survey (4566 deg$^2$), the Hyper Suprime-Cam Subaru Strategic Program (469 deg$^2$), and the Kilo Degree Survey (825 deg$^2$). We highlight some noteworthy objects in the sample, including potentially projected systems; clusters with strong lensing features; clusters with active central galaxies or star formation; and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses, and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr.

astro-ph.CO↗

arXiv2020

Increasing the census of L and T dwarfs in wide binary and multiple systems using Dark Energy Survey DR1 and Gaia DR2 data

We present the discovery of 255 binary and six multiple system candidates with wide > 5" separation composed by ultracool dwarfs companions to stars, plus nine double ultracool dwarf systems. These systems were selected based on common distance criteria. About 90% of the total sample has proper motions available and 73% of the systems also satisfy a common proper motion criterion. The sample of ultracool candidates was taken from the Dark Energy Survey (DES) and the candidate stellar primaries are from Gaia DR2 and DES data. We compute chance alignment probabilities in order to assess the physical nature of each pair. We find that 174 candidate pairs with Gaia DR2 primaries and 81 pairs with a DES star as a primary have chance alignment probabilities < 5%. Only nine candidate systems composed of two ultracool dwarfs were identified. The sample of candidate multiple systems is made up of five triple systems and one quadruple system. The majority of the ultracool dwarfs found in binaries and multiples are of early L type and the typical wide binary fraction over the L spectral types is 2-4%. Our sample of candidate wide binaries with ultracool dwarfs as secondaries constitutes a substantial increase over the known number of such systems, which are very useful to constrain the formation and evolution of ultracool dwarfs.

astro-ph.SR↗

arXiv2020

Reducing ground-based astrometric errors with Gaia and Gaussian processes

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.

astro-ph.IM↗

arXiv2020

Dark Energy Survey Year 1 Results: Cosmological Constraints from Cluster Abundances, Weak Lensing, and Galaxy Correlations

Combining multiple observational probes is a powerful technique to provide robust and precise constraints on cosmological parameters. In this letter, we present the first joint analysis of cluster abundances and auto/cross correlations of three cosmic tracer fields measured from the first year data of the Dark Energy Survey: galaxy density, weak gravitational lensing shear, and cluster density split by optical richness. From a joint analysis of cluster abundances, three cluster cross-correlations, and auto correlations of galaxy density, we obtain $Ω_{\rm{m}}=0.305^{+0.055}_{-0.038}$ and $σ_8=0.783^{+0.064}_{-0.054}$. This result is consistent with constraints from the DES-Y1 galaxy clustering and weak lensing two-point correlation functions for the flat $νΛ$CDM model. We thus combine cluster abundances and all two-point correlations from three cosmic tracer fields and find improved constraints on cosmological parameters as well as on the cluster observable--mass scaling relation. This analysis is an important advance in both optical cluster cosmology and multi-probe analyses of upcoming wide imaging surveys.

astro-ph.CO↗

arXiv2020

The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is apply weights to a spectroscopic sample so that their weighted photometry distribution matches the target sample. In this work we estimate the \textit{selection bias} in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in DES as an example data set but the implications generalise to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of $Δ~z\sim0.015$ in the weighted mean redshift of different redshift intervals. To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the $Δ~z=0.005-0.05$ level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

astro-ph.GA↗

arXiv2020

Weak Lensing of Type Ia Supernovae from the Dark Energy Survey

We consider the effects of weak gravitational lensing on observations of 196 spectroscopically confirmed Type Ia Supernovae (SNe Ia) from years 1 to 3 of the Dark Energy Survey (DES). We simultaneously measure both the angular correlation function and the non-Gaussian skewness caused by weak lensing. This approach has the advantage of being insensitive to the intrinsic dispersion of SNe Ia magnitudes. We model the amplitude of both effects as a function of $σ_8$, and find $σ_8 = 1.2^{+0.9}_{-0.8}$. We also apply our method to a subsample of 488 SNe from the Joint Light-curve Analysis (JLA) (chosen to match the redshift range we use for this work), and find $σ_8 = 0.8^{+1.1}_{-0.7}$. The comparable uncertainty in $σ_8$ between DES-SN and the larger number of SNe from JLA highlights the benefits of homogeneity of the DES-SN sample, and improvements in the calibration and data analysis.

astro-ph.CO↗

arXiv2020

A DESGW Search for the Electromagnetic Counterpart to the LIGO/Virgo Gravitational Wave Binary Neutron Star Merger Candidate S190510g

We present the results from a search for the electromagnetic counterpart of the LIGO/Virgo event S190510g using the Dark Energy Camera (DECam). S190510g is a binary neutron star (BNS) merger candidate of moderate significance detected at a distance of 227$\pm$92 Mpc and localized within an area of 31 (1166) square degrees at 50\% (90\%) confidence. While this event was later classified as likely non-astrophysical in nature within 30 hours of the event, our short latency search and discovery pipeline identified 11 counterpart candidates, all of which appear consistent with supernovae following offline analysis and spectroscopy by other instruments. Later reprocessing of the images enabled the recovery of 6 more candidates. Additionally, we implement our candidate selection procedure on simulated kilonovae and supernovae under DECam observing conditions (e.g., seeing, exposure time) with the intent of quantifying our search efficiency and making informed decisions on observing strategy for future similar events. This is the first BNS counterpart search to employ a comprehensive simulation-based efficiency study. We find that using the current follow-up strategy, there would need to be 19 events similar to S190510g for us to have a 99\% chance of detecting an optical counterpart, assuming a GW170817-like kilonova. We further conclude that optimization of observing plans, which should include preference for deeper images over multiple color information, could result in up to a factor of 1.5 reduction in the total number of followups needed for discovery.

astro-ph.HE↗

arXiv2020

$μ_{\star}$ Masses: Weak Lensing Calibration of the Dark Energy Survey Year 1 redMaPPer Clusters using Stellar Masses

We present the weak lensing mass calibration of the stellar mass based $μ_{\star}$ mass proxy for redMaPPer galaxy clusters in the Dark Energy Survey Year 1. For the first time we are able to perform a calibration of $μ_{\star}$ at high redshifts, $z>0.33$. In a blinded analysis, we use $\sim 6,000$ clusters split into 12 subsets spanning the ranges $0.1 \leqslant z<0.65$ and $μ_{\star}$ up to $\sim 5.5 \times 10^{13} M_{\odot}$, and infer the average masses of these subsets through modelling of their stacked weak lensing signal. In our model we account for the following sources of systematic uncertainty: shear measurement and photometric redshift errors, miscentring, cluster-member contamination of the source sample, deviations from the NFW halo profile, halo triaxiality and projection effects. We use the inferred masses to estimate the joint mass--$μ_{\star}$--$z$ scaling relation given by $\langle M_{200c} | μ_{\star},z \rangle = M_0 (μ_{\star}/5.16\times 10^{12} \mathrm{M_{\odot}})^{F_{μ_{\star}}} ((1+z)/1.35)^{G_z}$. We find $M_0= (1.14 \pm 0.07) \times 10^{14} \mathrm{M_{\odot}}$ with $F_{μ_{\star}}= 0.76 \pm 0.06$ and $G_z= -1.14 \pm 0.37$. We discuss the use of $μ_{\star}$ as a complementary mass proxy to the well-studied richness $λ$ for: $i)$ exploring the regimes of low $z$, $λ<20$ and high $λ$, $z \sim 1$; $ii)$ testing systematics such as projection effects for applications in cluster cosmology.

astro-ph.CO↗

arXiv2020

OzDES multi-object fibre spectroscopy for the Dark Energy Survey: Results and second data release

We present a description of the Australian Dark Energy Survey (OzDES) and summarise the results from its six years of operations. Using the 2dF fibre positioner and AAOmega spectrograph on the 3.9-metre Anglo-Australian Telescope, OzDES has monitored 771 AGN, classified hundreds of supernovae, and obtained redshifts for thousands of galaxies that hosted a transient within the 10 deep fields of the Dark Energy Survey. We also present the second OzDES data release, containing the redshifts of almost 30,000 sources, some as faint as $r_{\mathrm AB}=24$ mag, and 375,000 individual spectra. These data, in combination with the time-series photometry from the Dark Energy Survey, will be used to measure the expansion history of the Universe out to $z\sim1.2$ and the masses of hundreds of black holes out to $z\sim4$. OzDES is a template for future surveys that combine simultaneous monitoring of targets with wide-field imaging cameras and wide-field multi-object spectrographs.

astro-ph.CO↗

arXiv2020

DES16C3cje: A low-luminosity, long-lived supernova

We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of $\lesssim1500$ km s$^{-1}$, and the light curve shows an initial peak that fades after 50 days before slowly rebrightening over a further 100 days to reach an absolute brightness of M$_r\sim -15.5$ mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of $^{56}$Co but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either i) a low explosion energy (0.11 foe) and relatively large $^{56}$Ni production of 0.075 M$_{\odot}$ from a $\sim15$ M$_{\odot}$ red supergiant progenitor typical of other SNe II, or ii) a relatively compact $\sim40$ M$_{\odot}$ star, explosion energy of 1 foe, and 0.08 M$_{\odot}$ of $^{56}$Ni. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of $\sim0.5\times{10^{-8}}$ M$_{\odot}$ s$^{-1}$.

hep-ph↗

arXiv2020

Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis

We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultra-faint dwarf galaxy Grus~II. All stars exhibit a higher than expected $\mathrm{[Mg/Ca]}$ ratio compared to metal-poor stars in other ultra-faint dwarf galaxies and in the Milky Way halo. Nucleosynthesis in high mass ($\geqslant 20$M$_\odot$) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (3) stars suggest the chemical enrichment of Grus~II could have occurred through substantial high-mass stellar evolution and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it can not be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture ($r$-process) elements. The abundance pattern of the $r$-process elements in this star matches the scaled $r$-process pattern of the solar system and $r$-process enhanced stars in other dwarf galaxies and in the Milky Way halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of $r$-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus~II would increase the likelihood of any of these events occurring. The time delay between the $α$ and $r$-process element enrichment of the galaxy favors a neutron star merger as the origin of the $r$-process elements in Grus~II.

astro-ph.SR↗

arXiv2020

Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey

Despite vast improvements in the measurement of the cosmological parameters, the nature of dark energy and an accurate value of the Hubble constant (H$_0$) in the Hubble-Lemaître law remain unknown. To break the current impasse, it is necessary to develop as many independent techniques as possible, such as the use of Type II supernovae (SNe II). The goal of this paper is to demonstrate the utility of SNe II for deriving accurate extragalactic distances, which will be an asset for the next generation of telescopes where more-distant SNe II will be discovered. More specifically, we present a sample from the Dark Energy Survey Supernova Program (DES-SN) consisting of 15 SNe II with photometric and spectroscopic information spanning a redshift range up to 0.35. Combining our DES SNe with publicly available samples, and using the standard candle method (SCM), we construct the largest available Hubble diagram with SNe II in the Hubble flow (70 SNe II) and find an observed dispersion of 0.27 mag. We demonstrate that adding a colour term to the SN II standardisation does not reduce the scatter in the Hubble diagram. Although SNe II are viable as distance indicators, this work points out important issues for improving their utility as independent extragalactic beacons: find new correlations, define a more standard subclass of SNe II, construct new SN II templates, and dedicate more observing time to high-redshift SNe II. Finally, for the first time, we perform simulations to estimate the redshift-dependent distance-modulus bias due to selection effects.

astro-ph.HE↗

arXiv2020

The Host Galaxies of Rapidly Evolving Transients in the Dark Energy Survey

Rapidly evolving transients (RETs), also termed fast blue optical transients (FBOTs), are a distinct class of astrophysical event. They are characterised by lightcurves that decline much faster than common classes supernovae (SNe), span vast ranges in peak luminosity and can be seen to redshifts greater than 1. Their evolution on fast timescales has hindered high quality follow-up observations, and thus their origin and explosion/emission mechanism remains unexplained. In this paper we define the largest sample of RETs to date, comprising 106 objects from the Dark Energy Survey, and perform the most comprehensive analysis of RET host galaxies. Using deep-stacked photometry and emission-lines from OzDES spectroscopy, we derive stellar masses and star-formation rates (SFRs) for 49 host galaxies, and metallicities for 37. We find that RETs explode exclusively in star-forming galaxies and are thus likely associated with massive stars. Comparing RET hosts to samples of host galaxies of other explosive transients as well as field galaxies, we find that RETs prefer galaxies with high specific SFRs, indicating a link to young stellar populations, similar to stripped-envelope SNe. RET hosts appear to show a lack of chemical enrichment, their metallicities akin to long duration gamma-ray bursts and superluminous SN host galaxies. There are no clear relationships between properties of the host galaxies and the peak magnitudes or decline rates of the transients themselves.

astro-ph.GA↗

arXiv2020

A joint SZ-Xray-optical analysis of the dynamical state of 288 massive galaxy clusters

We use imaging from the first three years of the Dark Energy Survey to characterize the dynamical state of 288 galaxy clusters at $0.1 \lesssim z \lesssim 0.9$ detected in the South Pole Telescope (SPT) Sunyaev-Zeldovich (SZ) effect survey (SPT-SZ). We examine spatial offsets between the position of the brightest cluster galaxy (BCG) and the center of the gas distribution as traced by the SPT-SZ centroid and by the X-ray centroid/peak position from Chandra and XMM data. We show that the radial distribution of offsets provides no evidence that SPT SZ-selected cluster samples include a higher fraction of mergers than X-ray-selected cluster samples. We use the offsets to classify the dynamical state of the clusters, selecting the 43 most disturbed clusters, with half of those at $z \gtrsim 0.5$, a region seldom explored previously. We find that Schechter function fits to the galaxy population in disturbed clusters and relaxed clusters differ at $z>0.55$ but not at lower redshifts. Disturbed clusters at $z>0.55$ have steeper faint-end slopes and brighter characteristic magnitudes. Within the same redshift range, we find that the BCGs in relaxed clusters tend to be brighter than the BCGs in disturbed samples, while in agreement in the lower redshift bin. Possible explanations includes a higher merger rate, and a more efficient dynamical friction at high redshift. The red-sequence population is less affected by the cluster dynamical state than the general galaxy population.

astro-ph.GA↗

arXiv2020

Milky Way Satellite Census. II. Galaxy--Halo Connection Constraints Including the Impact of the Large Magellanic Cloud

The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy--halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated $6\pm 2$ observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last $2\ \rm{Gyr}$ at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $3.2\times 10^{8}\ M_{\rm{\odot}}$ at $95\%$ confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above $10^{6}\ M_{\rm{\odot}}$, highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.

astro-ph.GA↗

arXiv2020

The Mystery of Photometric Twins DES17X1boj and DES16E2bjy

We present an analysis of DES17X1boj and DES16E2bjy, two peculiar transients discovered by the Dark Energy Survey (DES). They exhibit nearly identical double-peaked light curves which reach very different maximum luminosities (M$_\mathrm{r}$ = -15.4 and M$_\mathrm{r}$ = -17.9, respectively). The light curve evolution of these events is highly atypical and has not been reported before. The transients are found in different host environments: DES17X1boj was found near the nucleus of a spiral galaxy, while DES16E2bjy is located in the outskirts of a passive red galaxy. Early photometric data is well fitted with a blackbody and the resulting moderate photospheric expansion velocities (1800 km/s for DES17X1boj and 4800 km/s for DES16E2bjy) suggest an explosive or eruptive origin. Additionally, a feature identified as high-velocity CaII absorption (v $\approx$ 9400km/s) in the near-peak spectrum of DES17X1boj may imply that it is a supernova. While similar light curve evolution suggests a similar physical origin for these two transients, we are not able to identify or characterise the progenitors.

astro-ph.HE↗

arXiv2020

STRIDES: Spectroscopic and photometric characterization of the environment and effects of mass along the line of sight to the gravitational lenses DES J0408-5354 and WGD 2038-4008

In time-delay cosmography, three of the key ingredients are 1) determining the velocity dispersion of the lensing galaxy, 2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and 3) estimating the external convergence $κ_\mathrm{ext}$ from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quasar systems, DES J0408-5354 and WGD 2038-4008. We use the Gemini, Magellan and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408-5354 and 2 groups in WGD 2038-4008using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the "flexion shift" criterion. We determine the probability distribution function of the external convergence $κ_\mathrm{ext}$ for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408-5354 is located in a significantly underdense environment, leading to a tight (width $\sim3\%$), negative-value $κ_\mathrm{ext}$ distribution. On the other hand, WGD 2038-4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter $κ_\mathrm{ext}$ of $\sim1\%$, as long as no external shear constraints are imposed.

astro-ph.GA↗