Talk Abstracts

DECam Status and Future [6.97 MB PDF]

Alistair Walker

DECam has been on-sky with the Blanco telescope since late 2012, and we expect to keep operating it well into the era of LSST. I will discuss status of the instrument, the operations modes, and describe some possible changes and improvements. The present meeting will inform on these topics.

Authors: Alistair Walker

NOAO Data Lab: Overview, Applications with DECam, Next Steps [14.85 MB PDF]

Leah Fulmer

The NOAO Data Lab seeks to empower astronomers to efficiently explore and analyze the largest datasets available through NOAO facilities, especially those from DECam (e.g. DECaLS, DECaPS, DES). Its primary objectives are to connect users with high-value catalogs through both user-defined and data discovery search forums, to build Python-based tools for the efficient visualization and analysis of data both within and beyond the Data Lab system, and to provide direct service to astronomers in order to optimize user experience. In this talk, I will introduce the various databases, modules, and services currently available within the Data Lab, offer an example science case for exploring the DECaPS database within a Jupyter Notebook, and outline the next steps for the Data Lab’s continued utility and accessibility.

Authors: Leah Fulmer, Knut Olsen, Stephanie Juneau

The photometric and astrometric properties of DECam as enablers of precision science [25.8 MB PDF]

Douglas Tucker

Precise and accurate calibration of a wide-field imager with the areal coverage of DECam is not a trivial task. In this talk, I will discuss the astrometric and photometric calibration of individual DECam images, as well as that of DECam surveys, with particular reference to the Dark Energy Survey (DES) and the Blanco Imaging of the Southern Sky (BLISS) survey.

Authors: Douglas L. Tucker

The DESI Imaging Legacy Surveys [4.34 MB PDF]

Martin Landriau

The Dark Energy Spectroscopic Instrument will map 25 million galaxies and quasars out to redshift 3.5 over 14,000 deg2 of sky. It will also measure redshifts for 10 million additional bright (r<19.5) galaxies to create a dense map of the low-redshift Universe. In order to select targets, three ground-based surveys are being (or have been) carried out at three telescopes. I will describe these surveys, including the DECam Legacy Survey (DECaLS), which is using DECam to image the DESI footprint in the South galactic cap, and in the North galactic cap at dec<32. I will discuss our most recent data releases and describe our upcoming 7th data release which will consist of catalogues generated from data obtained from DECam through March of this year.

Authors: Martin Landriau

Weak Lensing Mass Calibration with DECam: The Most Precise Mass—Scaling Relation Measurement To Date [3.64 MB PDF]

Thomas McClintock

Galaxy clusters are a powerful probe of cosmology. Observations of galaxy clusters using DECam made by the Dark Energy Survey (DES) have taken significant steps in order to allow galaxy clusters to become a powerful probe of the large scale structure of the Universe. Using gravitational weak lensing, DES has precisely measured the mean cluster mass -- optical richness scaling relation to 5% accuracy. This is the most stringent scaling relation of galaxy clusters performed to date, and has allowed for competitive constraints on the matter density and clustering amplitude of the Universe.

Authors: Thomas McClintock

Cosmological Parameter Constraints from the Dark Energy Survey Supernova Program Three Year Spectroscopic Sample [11.88 MB PDF]

Dillon Brout

We present cosmological parameter constraints from 251 spectroscopically confirmed Type Ia Supernovae (0.02 $<$ z $<$ 0.85) discovered during the first 3 years of the Dark Energy Survey Supernova Program. Type Ia supernovae, used as standardizable candles, probe the acceleration of the universe and are sensitive to the equation of state parameter for dark energy. The photometric calibration, photometric pipeline, additional low-z supernovae samples (z$<$.1), as well as the final cosmological results and systematics analysis are discussed.

Authors: Dillon

DECam at the Low Surface Brightness Limit: Detection of Diffuse Light in Galaxies and Galaxy Clusters [3.88 MB PDF]

Yuanyuan Zhang

The enormous amount of data collected by DECam provides a great opportunity to study low surface brightness science, such as the faint diffuse light in galaxies and galaxy clusters. Through stacking the images of ~300 galaxy clusters from the Dark Energy Survey, we report the detection of diffuse intra-cluster light at a surface brightness level of 30 mag/arcsec^2 out to 1 Mpc from the cluster center. Despite their low surface brightness, our studies show that intra-cluster light is a significant component of galaxy cluster light. The stacking method is also applied to characterizing the light profile of luminous red galaxies to 200 kpc from the center, as well as studying the aureole component of DECam point spread function to 30 arcsecond and beyond.

Authors: Yuanyuan Zhang

The DECam Plane Survey [4.88 MB PDF]

Edward Schlafly

The DECam Plane Survey is a five-band optical and near-infrared survey of the southern Galactic plane with the Dark Energy Camera (DECam) at Cerro Tololo. The survey is designed to reach past the main-sequence turn-off at the distance of the Galactic center through a reddening E(B − V) of 1.5 mag. The survey has a typical single-exposure depth of 23.7, 22.8, 22.2, 21.8, and 21.0 mag in the grizY bands, with seeing around 1 arcsecond. The footprint covers the Galactic plane with |b| < 4◦, 5◦ > l > −120◦. The survey pipeline simultaneously solves for the positions and fluxes of all the sources in each image, delivering positions and fluxes of roughly two billion stars with up to 5 mmag repeatability. Most of these objects are highly reddened and deep in the Galactic disk, probing the structure and properties of the Milky Way and its interstellar medium. The full survey---fully-processed images and calibrated catalogs---is publicly available.

Authors: Edward Schlafly

Stellar Streams Discovered in the Dark Energy Survey [2.5 MB PDF]

Nora Shipp

We present the discovery of new stellar streams within the Dark Energy Survey (DES). The DES data covers ∼5000 sq. deg. to a depth of g > 23.5 with a relative photometric calibration uncertainty of < 1%. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of ∼50 kpc. Our analysis of the DES data has led to the discovery of eleven new stellar streams, improved observations of four previously known streams, and revealed evidence of extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The study of this ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way.

Authors: Nora Shipp

Mapping the reddening and Extinction towards the Galactic Bulge from Panchromatic Photometry of RR Lyrae Light Curves [8.2 MB PDF]

Abhijit Saha

We have obtained time spaced observations with DECam in 5 bands (u,g,r,i,z) in 6 fields towards the Galactic Bulge. The primary purpose was to measure and use the colors of RR Lyrae stars at their minimum light phases, where their instrinsic colors are predictable to a few percent, to map the reddening to the bulge along different sight lines. The data set is useful for a variety of other studies as well. We present here the reddening map with sub-arc-minute resolution towards the DECam field centered on the well known Baade's Window. Aside from revealing fascinating structure in the dust and indications that the reddening in this direction is different from the standard law, our procedure allows us to produce a de-reddened color-magnitude diagram that reveals hitherto unidentified components in the stellar population in the bulge.

Authors: A. Saha, A.K. Vivas, E. Olszewski et al.

Uncovering the SMASHed up Magellanic Clouds

David Nidever

Our knowledge of the formation and evolution of dwarf galaxies is limited. To gain a better understanding of the formation history of the nearby Small and Large Magellanic Clouds, SMASH (Survey of the MAgellanic Stellar History) has imaged ~2400 square degrees (at 20% filling factor) to 24th mag in gri (uz~23). These observations are alllowing us to map the expected stellar debris, extended stellar populations, and star formation histories of the Clouds with unprecedented fidelity. I will present SMASH results on the stellar peripheries of the Magelllanic Clouds that are helping us piece together the complication intercation history of these nearby dwarf galaxies.

Authors: David Nidever, Knut Olsen

DECam photometry covering the entirety of the puzzling Omega Cen globular cluster [16.61 MB PDF]

Annalisa Calamida

I will present multi-band photometry based on a catalog of ~2 million cluster members for a field of view of ~5x5 degrees across Omega Cen. Data were collected with DECam and combined with Hubble Space Telescope catalogs of the central regions of the cluster. The unprecedented photometric accuracy, depth and field coverage allowed us for the first time to investigate the spatial distribution of Omega Cen multiple populations from the core to the tidal radius and beyond, confirming its very complex structure. The color-magnitude diagrams show preliminary evidence for the presence of extra-tidal stars and differences in the spatial distribution of the stellar populations. We found that the frequency of blue main-sequence stars is increasing compared to red main-sequence stars in the outskirts of the cluster. Stars belonging to the reddest red-giant branch also show a more extended spatial distribution in the outskirts of Omega Cen, a region never explored before. Both these stellar sub-populations, according to spectroscopic measurements, are more metal-rich compared to the cluster main stellar population. These findings, once confirmed, make Omega Cen the only stellar system currently known where metal-rich stars have a more extended spatial distribution compared to metal-poor stars.

Authors: Annalisa Calamida, G. Strampelli, A. Rest, G. Bono, I. Ferraro, A. Saha, G, Iannicola, D. Scolnic, D. James, C. Smith, A. Zenteno

Probing the halo of the Milky Way beyond 100 kpc with RR Lyrae [20.01 MB PDF]

Jeff Carlin

Stars in the outermost halo of the Milky Way are vital tracers of the mass of our Galaxy. Furthermore, beyond ~100 kpc from the Galactic center, most (or perhaps all) of the stars are likely to be in faint dwarf galaxies or tidal debris from recently accreted dwarfs, making the outer reaches of the Galaxy important for understanding the Milky Way’s accretion history. Confirmed stars are scarce at these distances because they are difficult to securely identify. Pulsating variables such as RR Lyrae are ideal probes of the distant halo because they are readily identified in time-series data, are intrinsically bright and thus can be seen at large distances, and follow well-known period-luminosity relations that enable precise distance measurements. We present results from our program to find RR Lyrae using deep DECam time series data (from the HiTS supernova survey as well as our own observing program) covering ~350 square degrees. Our sample of distant RR Lyrae more than doubles the number of known Milky Way stars beyond distances of ~150 kpc. Among these, we find two distinct groups of two and three stars that are members of the Leo IV and Leo V ultra-faint dwarf galaxies, located at distances of ~145 kpc and ~175 kpc, respectively. We derive the stellar density as a function of Galactocentric radius, extending to more than 250 kpc from the Galactic center. This sample of RR Lyrae provides a set of important probes of the mass of the Milky Way and the accretion origin of the outer Galactic halo.

Authors: Jeff Carlin

Stellar Mass Growth of Massive Central Galaxies [13.37 MB PDF]

John Moustakas

Massive galaxies, the most massive of which are generally found at the centers of the largest dark matter halos in the universe, provide a unique laboratory for investigating several longstanding problems in galaxy formation and evolution. Despite their importance, however, measurements of the mass assembly and star formation histories of massive galaxies remain discordant and controversial, resulting in significant uncertainties in how numerical simulations treat gas cooling, star formation, and feedback from supernovae and supermassive black holes in massive halos. To address these issues, we have measured accurate integrated stellar masses of more than 50,000 massive central galaxies at z<0.5 using new deep, wide-area optical and mid-infrared imaging from the Legacy Surveys ( We find a non negligible reservoir of stellar mass in the low surface-brightness outer envelopes of the central galaxies in our sample, which has wide-ranging implications for inferences of the efficiency of star formation and the intensity of AGN feedback in massive dark matter halos.

Authors: John Moustakas, Dustin Lang, Arjun Dey, Eduardo Rozo, Eli Rykoff, David Schlegel, & Risa Wechsler

The LAGER Project: Probing Reionization at z~7 with the First Narrowband Filter on DECam [20.45 MB PDF]

Zhenya ZHENG

The resonant properties of Lya photons provide powerful tests of reionization via the statistical analysis of Lya galaxies (LAEs). While hundreds of LAEs have been efficiently detected with deep narrowband surveys up to z = 6.6, they are largely missing at z >~ 7. Is the decline of LAEs at z >~ 7 due to neutral intergalactic medium (IGM), or a decline in CCD sensitivities at 1 micron, or a change in intrinsic properties of LAEs? To answer these questions, we are taking the definitive narrowband LAE survey project at z ~ 7 -- “Lyman Alpha Galaxies in the Epoch of Reionization (LAGER)”. This survey exploits DECam's uniquely large FOV and QE in the near-infrared, as well as a custom narrowband filter at 9640AA built for DECam. This survey is the largest narrowband survey project for z ~ 7 galaxies, and it is also the first narrowband imaging survey with DECam. By testing the apparent decline in the characteristic luminosity of 23 Lya galaxies found in the central 1.4deg x 1.4deg LAGER-COSMOS field, which is the largest Lya galaxy sample at z ~ 7 to date, we have constrained a neutral hydrogen fraction of the intergalactic medium (IGM) of ~40-60% at z ~ 7 (Zheng et al. 2017). More interestingly, we have found an excess of ultra luminous Lya galaxies indicating an ionized bubble in that epoch.

In this talk, I’ll also report the unique power of narrowband imaging with DECam.

Authors: Zhenya Zheng and the LAGER team

Exploring Reionization-Era Quasars with DESI Legacy imaging Survey and UKIRT Hemisphere Survey

Jinyi Yang

We are combining DESI Legacy imaging Survey with near-infrared surveys like UKIRT Hemisphere Survey (UHS), as well as Wide-field Infrared Survey Explore (WISE) mid-infrared survey to search distant quasars at the epoch of reionization era. In the past year, we have successfully discovered 15 quasars at z>6.5, doubled the number of previously known quasars at this redshift range and constructed the largest uniformly selected quasar sample at the reionization era. Using this sample, we measured the quasar luminosity function at z>6.5 for the first time. We are also working on the studies of cosmic reionization history and black hole growth based on this unique quasar sample.

Authors: Jinyi Yang, Xiaohui Fan, Feige Wang

Deeper, Wider, Faster: Using DECam to help chase the fastest bursts in the Universe [69.07 MB PDF]

Tim Abbott

The Deeper, Wider, Faster (DWF) program coordinates over 50 facilities worldwide and in space, including radio through gamma-ray telescopes, high-energy photon, particle and gravitational wave detectors, to detect and follow up fast transients (millisecond-to-hours duration). Fast transients include fast radio bursts, gravitational waves and their counterparts, supernova shock breakouts, various GRBs, flare stars, and collisions of Type Ia supernovae with companion stars. DWF is the only program of its kind and is a novel use of DECam, as well as a pathfinder for LSST to characterise the fast transient Universe. DWF has three main components: (1) Simultaneous observations for fast transient detections with ~20 facilities (e.g., Parkes, ASKAP, Molonglo, DECam, Swift, and HXMT) for deep, wide-field, fast-cadenced observations of the same field at the same time, (2) Real-time radio, optical and high-energy supercomputer data processing (in seconds) and fast transient identification within minutes of the light hitting the telescopes, via software and human visual inspection using sophisticated visualisation technology, and (3) 1-10m-class rapid-response, conventional ToO, and later-time spectroscopic and imaging follow up of real-time identified events and their host galaxies using ~30 facilities such as Keck, VLT, Gemini, SALT, AAT, Lijiang, Swift, MWA, ATCA, GROND, SkyMapper, CNEOST, and the AST3-2 telescope in the Antarctic.

Authors: J. Cooke, I. Andreoni, T. Pritchard, and the DWF team

Multi-messenger Astronomy with DECam [30.64 MB PDF]

Marcelle Soares-Santos

The exciting prospect of new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events using the Dark Energy Camera (DECam). This talk presents the discovery of the optical transient associated with the neutron star merger GW170817 using DECam and discusses its implications for the role of DECam in this emerging field of multi-messenger cosmology with gravitational waves and optical data.

Authors: Marcelle Soares-Santos

Measuring the size distribution of small NEOs with DECam [6.43 MB PDF]

Lori Allen

We used the Blanco + Dark Energy Camera to measure the size distribution of near-Earth asteroids from 1km diameter to 10m. I will describe the survey and present results. Preliminary results, published in Trilling et al. 2017, imply a factor of 10 fewer NEOs at the small end of the distribution than was previously predicted.

Authors: L. Allen, F. Valdes, D. Trilling, D. Herrera, C. Fuentes, D. James, T. Axelrod, & J. Rajagopal

The variable star population in the Sextans dwarf spheroidal galaxy [4.57 MB PDF]

Kathy Vivas

Wide-field instruments such as DECam allow efficient surveys of large galaxies such as Sextans. We have conducted a variability survey in this galaxy in the g and r bands covering for the first time the full extension of this satellite of the Milky Way, which is located at 80 kpc from the Sun. Although the survey was designed to detect the short period SX Phoenicis population, we also recovered other types of variables. In total we identified 200 RR Lyrae stars, 7 anomalous cepheids, and 14 SX Phoenicis stars. In this talk I will discuss the properties of the variable stars in Sextans and the implications for our understanding of its stellar populations.

Authors: K. Vivas, J. Alonso-Garcia, M. Mateo, A. Walker, D. Nidever, B. Howard

DECam Microlensing Studies of Intermediate Mass Black Holes [3.48 MB PDF]

William Dawson

The discovery of gravitational waves from merging intermediate mass black holes (IMBHs) by LIGO is arguably among the most important scientific discoveries of the 21st century. The current rate of LIGO events favors such a large abundance that IMBHs (15-10^5 Msun) would make up the majority of dark matter (DM). We will discuss our ongoing DECam microlensing survey to search for similar IMBHs in our Milky Way. This is one of the select projects recommended by the DOE Cosmic Visions: New Ideas in Dark Matter report. While past microlensing surveys have only been efficient below 10 Msun, we are using paralensing as a means of surpassing this previous limitation. By carefully designing this survey we will enable the detection of these intermediate mass black holes based on their parallax microlensing signal, and thus enable this and future surveys to be sensitive to black holes in the Milky Way > 10 Msun. This survey will also open the door to precise mass measurements of individual black holes through follow-up observations of the complementary astrometric microlensing signal.

Authors: Will Dawson, Mark Ammons, Tim Axelrod, George Chapline, Agnieszka Cieplak, Alex Drlica-Wagner, Nathan Golovich, Jessica Lu, Michael Schneider, & Anja von der Linden

A DECAM Survey to unveil the hidden Galactic population of quiescent black holes [21.36 MB PDF]

Jorge Casares

We propose to exploit a novel strategy to uncover the Galactic population of quiescent black holes (BHs) in X-ray binaries. This is based on a new concept, the photometric mass function (PMF), which opens up the possibility of an efficient identification of dynamical BHs in large FOVs. It exploits the width of the Halpha emission line arising from the accretion disc, to be measured photometrically through a combination of custom Halpha filters. Details of the technique and survey strategy are given in Casares 2018
(MNRAS 473 5195).

We estimate that a dedicated survey of ∼800 deg2 at depth r~22 with three special Halpha filters are required to unveil >∼50 new dynamical BHs, a three-fold improvement over the known population. For comparison, a century would be needed to produce an enlarged sample of 50 dynamical BHs from X-ray transients at the current discovery rate. The survey, which we name HAWKs (after "HAlpha-Width Kilo-deg Survey”) will also deliver a census of other Halpha emitting objects - such as cataclysmic variables, accreting millisecond pulsars, symbiotic binaries, YSOs, etc.- to unprecedented depths. HAWKs will become a unique legacy survey for follow-up studies of Halpha emitting populations in the Galaxy. We estimate that ~100 nights will be required to complete HAWKs.

Authors: Jorge Casares

Mitigation of Photometric Systematics in Galaxy Clustering Measurements with Artificial Intelligence [2.6 MB PDF]

Mehdi Rezaie

In order to get a robust measurement of clustering of large scale structures, it is crucial to understand imaging systematics and mitigate for the effects. In my talk, I would like to present our idea of using Neural Networks, using DECam DR5, to learn how galaxy density (in particular Emission Line Galaxies) depends on imaging systematics such as galactic extinction. This approach will be beneficial to large galaxy surveys and complementary to other typical approaches of correcting systematic effects like linear/quadratic regression.

Authors: Mehdi Rezaie

Looking for Bubbles in LAGER

Sangeeta Malhotra

Because Lyman alpha photons are scattered by neutral hydrogen, the visibility of Lyman alpha emitting galaxies serves as a proxy indicator for locations of ionized gas in the intergalactic medium. The numbers of Lyman alpha galaxies recently discovered in the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) survey are appreciably lower than seen at lower redshifts, suggesting that the intergalactic medium at redshift 7 is partially neutral. By studying the spatial distribution of the galaxies that are observed, we can look for individual ionized bubbles. We present evidence that such bubbles have been identified in LAGER. Moreover, we argue that the ionizing photon production in the region near the brightest LAGER sources should be approximately sufficient to ionize their surroundings regardless of the bulk ionization state of the redshift seven universe.

Authors: Sangeeta Malhotra, James E. Rhoads, Zhenya Zheng, and the LAGER collaboration

ANTARES: Time-Domain Discovery in the Era of ZTF and LSST [50.03 MB PDF]

Thomas Matheson

The revolution in time-domain astronomy has arrived. Large-scale surveys are detecting events at an unparalleled rate. Discoveries of new and exotic objects abound. The traditional techniques of handling each detection individually will not scale to the current and future production. In just a few short years, the Large Synoptic Survey Telescope (LSST) will begin operations in Chile, while the Zwicky Transient Facility (ZTF) should be producing alerts by the time of
this meeting. With LSST, time-domain event production will jump by at least a factor of a hundred. The ANTARES project is a joint venture between NOAO and the University of Arizona Computer Science Department to develop a software infrastructure system to process time-domain events automatically at the scale and rate LSST will generate. I will describe the system, illustrate some filtering processes, and outline the path to an LSST-scale product. In addition, I will discuss the role DECam can play in this environment.

Authors: T. Matheson, A. Saha, M. Soraisam, G. Narayan, R. Snodgrass, J. Kececioglu, C. Scheidegger

Solar System Synergies in the Era of LSST [7.75 MB PDF]

Meg Schwamb

Over its 10 year lifespan, the Large Synoptic Survey Telescope (LSST) will catalog over 5 million Main Belt asteroids, almost 300,000 Jupiter Trojans, over 100,000 Near Earth Objects (NEOs), more than 40,000 Kuiper belt objects (KBOS), tens of interstellar objects, and thousands of comets. Many of these objects will receive hundreds of observations in multiple bandpasses. With access to the southern skies, DECam provides a unique opportunity for extended Solar System science when combiend with the LSST Wide-Fast-Deep Survey. In this talk, I will provide a brief status of LSST with respect to Solar System science. I will give an overview of the LSST Solar System Science Collaboration’s (SSSC) top priorities in the LSST era and outline ideas for how DECam observations can be paired with the LSST survey to achieve and exceed these goals.

Authors: Meg Schwamb

Summary and Next Steps from the DECam Data Splinter Meeting [4.71 MB PDF]

Adam Bolton

Authors: A. Bolton

Motivation for the DECam Future Discussion [5.94 MB PDF]

Arjun Dey

Authors: A. Dey