Talk Abstracts
The DECam System: Technical Characteristics [2.64 MB PDF]
Alistair Walker
The Dark Energy Camera (DECam)is a large-format mosaic CCD camera at the prime focus of the CTIO Blanco 4m telescope. It is well-integrated with, and reliant upon, telescope and facility systems. We describe the characteristics of the camera, what has changed with time - and what has not - over its more than two years of use. We will also cover changes that have been made to the telescope to improve the image quality.
Authors: Alistair Walker and Tim Abbott
Characteristics of DECam Data, the Usual and the Oddities [21.32 MB PDF]
Gary Bernstein
Extensive analysis of DECam engineering, science, and calibration exposures has revealed that the camera is mostly devoid of "personality," with largely stable response. I will describe the reduction steps necessary to obtain high-accuracy photometry and astrometry, mostly due to the wide field of view. DECam does have a few quirks, which can be straightforwardly corrected for the observing conditions encountered by the Dark Energy Survey. We expect to attain photometric and astrometric accuracies limited by atmospheric effects.
Authors: Gary Bernstein
Observing with DECam [21.9 MB PPTX]
David James
We present an overview of the procedures, protocols and capabilities of the Dark Energy Camera from the observer's point-of-view. A detailed description is provided of the software control system, SISPI, which allows the observer to interface with, and control, all operational aspects of the Dark Energy Camera. Specific emphasis is placed on the set-up and observing procedures of the camera, as well as how to monitor and control the observing environment to ensure a successful observing campaign for novices and experts alike.
Authors: D. James
Calibrating DECam data: the DECal and aTmCam calibration systems [1.38 MB PDF]
Jennifer Marshall
DECam has the potential to provide extremely high quality, high precision photometric measurements if the data are calibrated appropriately. Two calibration systems are now in use at CTIO that can be used to calibrate the spectral response of the DECam data. The DECal system is used ~once per month to measure and monitor the relative throughput of the telescope+DECam system as a function of wavelength and time. The aTmCam system autonomously monitors the atmospheric transmission of the site every night, producing a complete atmospheric transmission model ~once per hour. These two systems can be combined to produce photometric measurements with DECam having better than 1% precision.
Authors: Jennifer Marshall, Ting Li, Darren DePoy, David James
The DECam Community Pipeline [4.17 MB PDF]
Francisco Valdes
The DECam Community Pipeline (CP) provides calibrated science data products for all community programs through the NOAO Science Archive. This presentation describes the calibrations applied to produce the data products.
Authors: Francisco Valdes
The NOAO Science Archive - Present and Future [23.73 MB PDF]
Mark Dickinson
The NOAO Science Archive holds raw data from all NOAO telescopes and instruments, as well as pipeline-reduced data from its wide-field imagers, Mosaic, NEWFIRM and (now) DECam. It is the primary way for observers to retrieve their own data, and for other users to find valuable archival data after their proprietary periods end. Most recently, the Archive has started to incorporate and serve the reduced, calibrated data products from large DECam surveys, starting with the Year 1 data delivery from the Dark Energy Survey. I will describe the current state of the NOAO Science Archive, its likely future evolution, and its potential utility for DECam users everywhere.
Authors: Mark Dickinson
Dark Energy Survey Overview [2.43 MB PDF]
Christopher Miller
The Dark Energy Survey is using 525 nights on DECam over a 5-year period to image 5000 square degrees in 5 filters to a depth of ~24 in the r-band. I will present the current status and future plans for the survey and its footprint. I will also discuss the primary science drivers and the connections to other cosmological datasets. Finally, I will highlight new scientific results from Science Verification data.
Authors: Christopher J. Miller
Public Data Releases from the Dark Energy Survey [12.45 MB PDF]
Robert Gruendl
The Dark Energy Survey will image 5,000 square degrees in the South Galactic Cap in the grizY bands over 5 years along with a higher cadence survey of 10 supernova fields in the the griz bands. Now in the second year of the survey, the calibrated image products reduced by the DESDM pipelines at NCSA are becoming public and are available through the NOAO Science Archive. I will briefly describe the pipeline processing behind this first release, the planned improvements for future releases, and the data products being made available by the DES in this and future data releases.
Authors: Gruendl
What to Expect from DES Public Data [894 KB PDF]
Brian Yanny
The Dark Energy Survey (DES) has completed two years of data taking as of Feb 2015. In addition to all raw images becoming public one year after they are taken, DES Data Management (DESDM) is releasing detrended, calibrated single epoch exposures into the NOAO Science Archive each year. Finally, DES will have two public releases of reduced coadded exposures and fully searchable catalogs, currently scheduled for mid-year 2017 and 2020. We will discuss details of all these releases.
Authors: Brian Yanny
The Dark Energy Survey: results in Large Scale Structure from Science Verification data [4.59 MB PDF]
Ignacio Sevilla
The Dark Energy Survey (DES) is a 5000 square degree photometric survey with the goal of measuring the parameters of dark energy. In August 2013, it began survey operations using the DECam imager. Making measurements of Large Scale Structure using galaxy clustering is one of the primary science drivers of the experiment. When combined with other Dark Energy probes made with the same data, these measurements will enable either a strong validation of the current LCDM paradigm, or will show inconsistencies pointing towards a cosmology based on modified gravity or an evolving Dark Energy equation of state. Some of the more interesting results from this project will come not only from measuring the BAO scale, but also from obtaining the cross-correlation with the CMB signal, measuring the galaxy bias with high statistical precision and at multiple redshifts, and combining weak lensing and clustering measurements using the same dataset. In this contribution, we will describe ongoing efforts at making measurements using the initial Science Verification dataset (aproximately 150 square degrees) with special focus on understanding the systematics that will be important for later releases.
Authors: Ignacio Sevilla for the Dark Energy Survey Collaboration
The DECam Legacy Survey: A Progress Report [10.02 MB PDF]
Arjun Dey
I will present a progress report on the Dark Energy Camera Legacy Survey, describing the goals, current status, and lessons learned.
Authors: Arjun Dey + DECaLS Team
DECam NEO: A sensitive, wide-field search for near-Earth objects [9.03 MB PDF]
Lori Allen
Near Earth Objects (NEOs) are asteroids or comets whose perihelion distance is less than 1.3 AU. Current estimates suggest that large NEOs (diameter 140m or more) impact the earth every few thousand years on average. Smaller asteroids (30m-50m) are believed to impact the earth with an average frequency of ~100 years, but this estimate is highly uncertain, based in part on an incomplete understanding of the size distribution of NEOs below 100m. Until now, it has not been possible to measure the size distribution of these objects, because large-aperture telescopes have not been equipped with very wide-field imagers. Now, the large étendue of DECam+Blanco allows us to probe a previously unexplored region of NEO parameter space and therefore hazard space. We have recently initiated a 30-night survey with DECam, with the goal to measure the size distribution of NEOs below 100m. Here we report on preliminary results based on the first 10 nights of our survey.
Authors: L. Allen, F. Valdes, D. Trilling, D. James, D. Herrera, C. Fuentes, T. Axelrod, J. Rajagopal, M. Brown
The High cadence Transient Survey (HiTS): real-time detection of supernovae and other transients with DECam [5.57 MB PDF]
Francisco Forster
At the Center for Mathematical Modelling (CMM) of the University of Chile and the Millennium Institute for Astronomy (MAS) we have developed a novel transient detection pipeline to be used in real-time with data from the Dark Energy Camera (DECam). During five contiguous nights in the first week of March of 2014 we were able to achieve the real-time data analysis of more than 120 square degrees of the sky with a cadence of only two hours and a processing time of less than one exposure time for every image. We processed more than 400 billion pixels in total, leading to the discovery of 12 newly exploding SNe in almost real-time. We found thousands of previously unknown asteroids and hundreds of variable stars that can be used to map the structure of the outer parts of the Milky Way. In this talk I will discuss the survey design and the current status of the project, as well as some of the new tools we have developed for real time transient detection applications.
Authors: Forster, F; Maureira, J.C.; San Martin, J.; Cabrera, G.; Hamuy, M; Gonzalez-Gaitan, S.; Galbany. Ll.;Anderson, J.; de Jaeger, Th.; Bufano, M.; Kunkarayakti, H.; Hsiao, E.; Pignata, G.; Vera, E.; Smith. R.C.; Morrel, N.; Lira. P.; and PESSTO collaboration
Near-Earth Object Discovery Confirmation with DECam
Sarah Sonnett
Near-Earth Objects (NEOs) are asteroids or comets with perihelia < 1.3 AU. Discovering NEOs and determining their orbits and sizes is needed to assess the risk of an impact or explosion. NEO studies also enable detailed investigations of inner solar system objects and the processes that govern their physical and dynamical evolution. The NEOWISE space mission is currently discovering NEOs in the infrared, so that when paired with optical follow-up from the ground, precise orbits, albedos, and thermal inertia values can be calculated. We have secured a small amount of this follow-up time on DECam. Because many of our discoveries are best observed in the southern hemisphere, are very faint (V ~ 22.5), and have typically large position uncertainty maps, DECam has played a critical role in recovering our NEO discoveries. We will review our discovery and follow-up process as well as some of the science highlights from NEOs confirmed through our program.
Authors: S. Sonnett (JPL/CalTech), A. Mainzer (JPL/CalTech), J. Bauer (JPL/CalTech), T. Grav (Planetary Science Institute), J. Masiero (JPL/CalTech), C. Nugent (JPL/CalTech), E. Kramer (JPL/CalTech)
SMASH - Techniques and Science [15.78 MB PDF]
Knut Olsen
Recent work on the Magellanic Clouds has led to surprising new views of these iconic galaxies. We now know that their stellar populations extend over a vast area of sky, that they may be bound only loosely to the Milky Way, and that their mutual interaction has likely created a complex array of both gaseous and stellar tidal debris. The Survey of the MAgellanic Stellar History (SMASH) will map the structure of the Clouds and their environs with unprecedented fidelity. SMASH is imaging 480 square degrees of the southern sky with DECam, covering a ~2400 square degree area at 20% filling factor. With its depth of 24th mag in gri (and ~23 in uz), SMASH will (a) search for the stellar components of the Magellanic Stream and Leading Arm, (b) detect and map the extended smooth components and substructure of the Magellanic Clouds, and (c) derive spatially resolved, precise star formation histories out to large radii. Our first year of data reveal (1) Large Magellanic Cloud (LMC) stellar populations extending out to a radius of at least 19 deg (~17 kpc) in several directions, (2) clear signatures of two dominant LMC star formation episodes at intermediate radii as revealed by multiple subgiant branches, and (3) evidence for an expansive stellar substructure in the Milky Way halo at a distance of ~30 kpc.
Authors: Knut A. Olsen, David Nidever, Robert A. Gruendl, Gurtina Besla, Abi Saha, Edward Olszewski, Ricardo Munoz, Carme Gallart, Matteo Monelli, Alistair R. Walker, Robert D. Blum, Catherine C. Kaleida, Kathy Vivas, Steven R. Majewski, Dennis F. Zaritsky, Roeland P. Van Der Marel, Eric F. Bell, Blair Conn, Guy S. Stringfellow, Shoko Jin, Lara Monteagudo Nervion, Maria-Rosa Cioni, Noelia Noel, Nicolas Martin, Antonela Monachesi, Thomas de Boer, You-Hua Chu, Hwihyun Kim, David Martinez-Delgado, Lent C. Johnson, Andrea Kunder
The Search for Light Echoes of Historic SNe in the Southern Hemisphere with DECam [13.22 MB PDF]
Armin Rest
In recent years, light echoes of ancient SNe have been discovered with the Mosaic II cameras at the CTIO Blanco and KPNO Mayall telescopes. We have found light echoes in the LMC (Rest et al. 2005, 2008a) and near the historical Galactic events Cas A, Tycho, and Eta Car (Rest et al. 2008b, 2011a, 2012). However, searches for light echoes near the Kepler SN and SN 1006 have not yet been successful. We have started a search for light echoes in the southern hemisphere using DECam at the CTIO Blanco telescope. DECam is an excellent light echo detection system with its larger field of view and much faster read time compared to Mosaic II. This increases the efficiency of the search by more than a factor of 10, allowing us to cover significantly larger areas of the sky. We report on strategy, progress, current coverage, and first results of our project.
Authors: Rest, A. (STScI), Bianco, F. (NYU), Chornock, R. (Ohio U.), Clocchiatti, A. (U. de Catolica), Foley, R. J. (UIUC), James, D. (CTIO), Matheson, T. (NOAO), Narayan, G. (NOAO), Olsen, K. A. (NOAO), Points, S. (CTIO), Prieto, J. L. (U. D. Portales), Smith, R. C. (CTIO), Smith, N. (U. of Arizona), Suntzeff, N. B. (Texas A&M)), Welch, D. L. (McMaster U.), Zenteno, A. (CTIO)
Exploring Milky Way Halo Substructures from Large-Area Digital Sky [1.87 MB PDF]
Ting Li
Over the last two decades, large-area digital sky surveys have provided deep photometric catalogs of stars in our Galaxy. The ability to detect and characterize substructures in our halo has increased dramatically. These substructures show that the Milky Way Galaxy is a complex and dynamic structure that is still being shaped by the accretion and merging of neighboring smaller galaxies. Sharma et al. (2010) developed a density-based hierarchical group-finding algorithm to identify stellar halo substructures in a catalog of M-giants from the Two Micron All Sky Survey (2MASS). This algorithm uncovered 16 substructures in the Milky Way halo, six of which were unknown at the time. In this talk, I will discuss the spectroscopic follow-up observations of one of the six substructure candidates. The radial velocities and the metailicities derived from the spectra show that the stars selected have kinematic and abundance signatures consistent with a disrupted merger remnant in the Galactic potential. I will also briefly discuss the application of this group-finding algorithm on a catalog of main-sequence turnoff (MSTO) stars from the Dark Energy Survey, which are more sensitive to low-luminosity events than the 2MASS M-giant sample. With higher photometric precision at the faint magnitude limit, more substructures could potentially be revealed with the future photometric surveys and provide a complete census of our Galaxy’s recent accretion history.
Authors: Ting Li, Jennifer Marshall, Kathryn Johnston, Allyson Sheffield
The Detailed Substructure of the Milky Way Stellar Streams: DECam Imaging of the Eastern Banded Structure [3.97 MB PDF]
Jonathan Hargis
Observational studies of the Milky Way's halo substructure are an integral part of understanding galaxy formation in a cosmological context. For example, the numerous stellar streams of our Galaxy have provided direct evidence of the hierarchical nature of galaxy assembly. Their detailed study reveals the nature of the Milky Way's recent progenitors, and their morphologies may contain the observational signatures of numerous low mass dark subhalos predicted by LCDM theory. I will present an overview and some initial results of our DECam imaging program to map one of the nearest stellar streams, the Eastern Banded Structure (EBS; d~10 kpc), as well as its possible progenitor. Our imaging has a limiting magnitude approximately two magnitudes deeper than SDSS, nearly five magnitudes below the main sequence turnoff. In addition, our imaging studies serve as precursor LSST science, providing a rich data set for understanding how low surface brightness structures at faint magnitudes can be quantified in the era of LSST.
Authors: Jonathan R. Hargis, B. Willman (Haverford College), D. Sand (Texas Tech University), J. Strader (Michigan State University), J. H. Yoon (Univ of California Santa Barbara), R. Fadely (New York University), Carl Grillmair (Caltech/IPAC)
“Rich Field Photometry - Techniques and Science" [4.42 MB PDF]
Abhijit Saha
I will discuss issues related to stellar photometry in very crowded fields, and the use of a priori criteria that can be used to identify false detections and measurements. I will talk about implementation of a working "pipeline" style photometry process, and bringing these methods to bear on a synoptic study of select fields in the Galactic Bulge, using DECam. Some early results from this study will be shown: how multiband photometry of RR Lyraes is being used to produce reddening corrected color-magnitude diagrams of the bulge region with the aim of disambiguating disk and spheroid populations.
Authors: A. Saha
DECam Variability Surveys of the Galactic Bulge Survey Fields [4.57 MB PDF]
Robert Hynes
The Chandra Galactic Bulge Survey (GBS) is a shallow but wide multi-wavelength survey of X-ray sources along the line-of-sight to the inner Galactic Bulge, covering 12 square degrees above and below the plane. The depth is chosen to maximize the yield of quiescent X-ray binaries relative to less luminous X-ray sources, and the latitude to minimize extinction while giving up as little as possible of the Bulge source density. The GBS has identified 1640 X-ray sources, expected to be comprised primarily of X-ray binaries, cataclysmic variables, and active stars, with smaller populations such as nearby lower activity stars, protostars, massive stars, and background active galaxies. Most of the expected sources should have variable optical/IR counterparts, so wide-field optical and near-IR variability studies are ideal for identifying these counterparts in crowded Bulge fields. I will describe the central role being played by variability surveys within the GBS project. In particular I will highlight the tremendous power of DECam in efficiently producing massively multiplexed, high-cadence lightcurves of GBS sources.
Authors: Hynes, R.I., Johnson, C.B., Britt, C.T., Jonker, P.G., Torres, M.A.P., Maccarone, T.J., Steeghs, D., Greiss, S., Wu, J., Nelemans, G., Heinke, C., and The GBS Collaboration
Substellar Mass Objects in the Belt of Orion - What DECam Does for Us [7.14 MB PDF]
Frederick Walter
OB associations are ideal sites for probing the formation of low mass objects. Our "wide-field" near-IR (JHK) survey of ~18 sq deg in the Orion OB1a and OB1b associations using the CPAPIR camera on the SMARTS/CTIO 1.5m telescope revealed thousands of potential substellar mass members of this nearby OB association. Unfortunately, JHK colors do not discriminate well between foreground M dwarfs and 1-2 Myr-old substellar mass objects, which are expected to have late-M spectral types, so foreground contamination could be a significant problem.
In December we used 2 nights with DECam to obtain deep grizY images of 12 fields in and near the belt of Orion.
The purpose is to obtain optical colors of our candidates and fainter objects. The optical colors are very good discriminants between the M and early L spectral type objects. We intended to reach the planetary mass limit,
but were given bright sky (20-30 degrees from the full moon).
I will present an overview of the program to date, a summary of the DECam data (and how I'm using IDL to deal with 900 GB of fpacked data). In return, I will ask how to do a good photometric calibration of these images.
Authors: Frederick M Walter & Jacqueline K Faherty
Variable Stars in the Sextans Dwarf Spheroidal Galaxy [3.3 MB PDF]
Kathy Vivas
Pulsating stars below the horizontal branch (aka, dwarf cepheids) provide an interesting tool to study the stellar populations and structure of dSph galaxies since stars coming from different evolutionary paths may coexist in the region of the instability strip. The detection of these variables is challenging in distant systems because of their faint brightness and very short pulsation periods. We present preliminary results of a DECam project aimed to unveil the population of faint variables in the Sextans dSph galaxy.
Authors: Kathy Vivas (CTIO), Mario Mateo (University of Michigan), Javier Alonso-García (PUC, Chile), Alistair Walker (CTIO), David Nidever (University of Michigan)
Wide-Field Photometric Survey of Young Southern Open Clusters [830 KB PDF]
Jeffrey Cummings
Star clusters are an observational foundation for stellar astrophysics, provide essential information for the study of Galactic structure and evolution, and are invaluable environments for analysis of stellar and chemical evolution.
There are few fields in astrophysics that do not in some way rely on results derived from open cluster analysis. Our project is a uniform study of young southern open clusters using DECam. We have obtained ugriz photometry of 12 carefully chosen nearby and rich clusters, where their full extent, if not the entire cluster, have previously only been poorly studied. DECam for the first time has allowed efficient and deep observation these large clusters within a single field of view. Given their young ages (ranging from 25 to 350 Myr), deep and wide-field photometry of this sample of clusters will form a strong foundation to address three outstanding astrophysical questions: 1.) What is the initial mass function (IMF) of stars and does it vary? 2.) What types of mixing and diffusion may be taking place in stellar interiors, and how do they vary with mass and metallicity? 3.) What is the threshold mass separating white dwarf formation from Type II supernovae?
Authors: Jeffrey Cummings, Douglas Geisler, Jason Kalirai, P.-E. Tremblay, F. Mauro, C. Deliyannis
Tracing Galaxy Group Assembly through Fossil Tidal Features [22.59 MB PDF]
Iraklis Konstantopoulos
Over cosmic time galaxies evolve from young, blue disks to old, red spheroids. The density of their environment plays a major role (Dressler et al., 1980, ApJ, 236, 351), hence studies have so far focussed on galaxy clusters. There, galaxies interact with multiple partners in quick succession and thus age faster than their isolated counterparts. However, the large membership of clusters results in the simultaneous action of various physical processes, therefore hindering the identification of those mechanisms that dominate galaxy evolution. Furthermore, populous clusters represent just 2% of the stellar mass in the present-day universe (Eke et al., 2005, MNRAS, 362, 1233), with looser groupings dominating in local redshift surveys (e.g., Small et al., 1999, ApJ, 524, 31).
Enter compact galaxy groups (CGs). With similar densities as clusters but few members they enable an intimate understanding of every galaxy and the physical processes at play. During semesters 2014A and B we deeply imaged eight CGs with DECam in three bands (and an additional group in one band), with the aim of tracing their assembly history. These data are deep enough, and of high-enough image quality, to serve as a legacy dataset in the pre-LSST-era, and will remain state-of-the-art for the next decade. For our science, they present an important step toward understanding whether CGs are a class of grouping that could occur at any redshift, or a privilege of the cosmological current era. With analysis now underway, preliminary results reveal tidal features in all nine groups in our sample, although one group shows no linkages between galaxies, just extensions to individual galaxy disks. This group, HCG7, has in the past been suggested as a first-infall group, one that is coming together right now, at redshift zero. I will examine this tantalising prospect and review our work toward untangling the assembly histories of the nine groups through age-dating their tidal debris and various ancillary information. Finally, I will present ideas and solicit input for methods through which the legacy value of these wide-field images can be realised.
Authors: Iraklis Konstantopoulos, Jane Charlton, Michael Rodruck, David James, Dane Kleiner
Lyman-Alpha Galaxies at the End of Reionization with DECam [4.06 MB PDF]
Zhenya Zheng
Lyα photons from galaxies are resonantly scattered by neutral inter-galactic medium (IGM), leading to an apparent decline in the luminosity function of Lyα galaxies. Our group pioneered the use of Lyα emitters to show that the IGM is ionized at z = 6.5 (Malhotra & Rhoads 2004). Several small surveys since then indicate weakening of the Lyα galaxies at z ∼ 7, implying a rapid reionization between z=7 and z=6.5. However, due to the limited survey area, very few LAEs are confirmed at z >~ 7. To take the convenience of large FOV and good performance of DECam, we are building a narrowband filter at 9700A for DECam, to effectively hunt for LAEs at z=7. In this talk, we will introduce our DECam narrowband survey, compare it with current z>~7 narrowband surveys, and present how the DECam NB survey result will constrain the ionization fraction of our Universe at z=7. Basically, we expect to detect several hundred Lya galaxies at z~7, and find the neutral fraction of our Universe through both Lya Luminosity function and Clustering, as well as the Lya line profile in the followup spectroscopic work. Our survey may also be effective to find high-z quasars, Lyman break galaxies and low-z emission line galaxies, which will help to determine the faint end (for LBG and ELG) and bright end (for quasar) of their luminosity function.
Authors: Zhenya Zheng, James Rhoads, Junxian Wang, Sangeeta Malhotra, Leopoldo Infante
Observing the electromagnetic counterparts of gravitational wave events with DECam: opportunities and potential impact
Marcelle Soares-Santos
First detections of coalescing neutron star binaries by a dedicated network of gravitational wave detectors are widely expected to happen within this decade. This long sought groundbreaking achievement will inaugurate new avenues for astrophysical studies. As discussed in this talk, DECam is in position to play a crucial role in that scenario. I describe plans to use DECam to followup gravitational wave events in search for their electromagnetic counterparts in optical bandpasses. Such hypothesized counterparts are supernova-like events resulting from the decay of neutron-rich radioactive species synthesized during the merger. They are faint, red, and fast decaying transients which impose an observational challenge for followup programs. In addition, early gravitational wave detectors provide poor sky localization for their candidate events, resulting in search regions of tens of square degrees. With a 3 square degree field of view, a 4 meter telescope, and specially red-sensitive CCDs, DECam is the ideal instrument to meet those challenges. It is also unique in the southern hemisphere. First coordinated detection of electromagnetic and gravitational radiation from merger events are a thrilling prospect for the DECam community.
Authors: Marcelle Soares-Santos
Measuring the Free-Floating Planet Mass Function with DECam and K2 [6.9 MB PDF]
Matthew Penny
The distribution of mass in free-floating planets holds vital information on the formation and subsequent evolution of the planetary systems from which they were ejected.
In the spring of 2016 the ninth campaign of K2 (the extended, two-wheel Kepler mission) will be targeted towards the Galactic bulge, where it will perform the first wide-field, space-based microlensing survey. This ~5 square degree survey will discover tens of free-floating planets by itself, but its real value will come from simultaneous ground-based observations that will provide parallax measurements. However, in order to convert these parallaxes into the first ever free-floating planet mass measurements, it is necessary to survey from the ground in more than one color at high cadence. The current dedicated microlensing survey telescopes do not have sufficient etendue to achieve the necessary depth and cadence to enable these mass measurements, but with 20x the etendue of the OGLE microlensing telescope DECam does.
The K2 microlensing survey will only happen once, and so the upcoming opportunity is the only chance we will have to measure the masses of enough free-floating planets to characterize their mass function. DECam is the only instrument in the world that can ensure this measurement is made.
The 6-square-degree, 80-night survey required to measure the free-floating planet mass function would also be a boon to other fields. The K2-DECam fields lie on the ecliptic so would enable an extremely deep search for objects like Sedna and 2012 VP113 in the inner Oort cloud, and from the survey data alone allow their orbits, colors and spin rates to be measured. The multicolor high-cadence monitoring would also enable a survey of more than 10^5 M-dwarfs to measure the energy distribution of large flares that could have a large impact on the habitability of planets orbiting the majority of the Galaxy's stars.
Authors: Matthew Penny
Probabilistic photometric redshift in the era of petascale astronomy [6.39 MB PDF]
Matias Carrasco Kind
Photometric redshifts (photo-z) are quickly becoming a critical measurement for large photometric galaxy surveys and there has been a significant development in this area in the last decade. Given the enormous amount of imaging data we are expecting to be available in the upcoming years, there is a need for fast, robust and more complex algorithms to compute and store not only a photo-z single estimate but also its probability density function.
In this talk I will review some of the state-of-the-art machine learning and data mining algorithms to compute, combine and store photo-z PDFs for large galaxy surveys. I will discuss how, a supervised machine learning technique , a unsupervised technique and a standard template fitting approach can be combined together in a Bayesian framework to improve the accuracy of the photo-z PDF as well as reducing the fraction of outliers in a completely new approach. I will also discuss how we can reduce the amount of storage of individual PDFs by using sparse representation techniques with a compression rate of 90% with an reconstruction accuracy of 99.8% using only 10 to 20 4-byte integers per galaxy which will allow us to store several techniques in a reduced amount of space which is becoming critical for current photometric surveys as several hundred million objects are expected. I will finalize by showing recent progress on how to implement and access these photo-z PDF from a SQL database using advance techniques allowing us for the first time to deal with these objects directly from the database and in fast and efficient manner with no precedents. The focus of this talk would be more into how we have integrated new functions and types to handle photo-z PDF into the DESDM Database and how this can be the foundation of including scientific scripting in SQL format making use of the DB resources.
Authors: Matias Carrasco Kind + DESDM NCSA team
The DECam System: Technical Characteristics [2.64 MB PDF]
Alistair Walker
The Dark Energy Camera (DECam)is a large-format mosaic CCD camera at the prime focus of the CTIO Blanco 4m telescope. It is well-integrated with, and reliant upon, telescope and facility systems. We describe the characteristics of the camera, what has changed with time - and what has not - over its more than two years of use. We will also cover changes that have been made to the telescope to improve the image quality.
Authors: Alistair Walker and Tim Abbott
Characteristics of DECam Data, the Usual and the Oddities [21.32 MB PDF]
Gary Bernstein
Extensive analysis of DECam engineering, science, and calibration exposures has revealed that the camera is mostly devoid of "personality," with largely stable response. I will describe the reduction steps necessary to obtain high-accuracy photometry and astrometry, mostly due to the wide field of view. DECam does have a few quirks, which can be straightforwardly corrected for the observing conditions encountered by the Dark Energy Survey. We expect to attain photometric and astrometric accuracies limited by atmospheric effects.
Authors: Gary Bernstein
Observing with DECam [21.9 MB PPTX]
David James
We present an overview of the procedures, protocols and capabilities of the Dark Energy Camera from the observer's point-of-view. A detailed description is provided of the software control system, SISPI, which allows the observer to interface with, and control, all operational aspects of the Dark Energy Camera. Specific emphasis is placed on the set-up and observing procedures of the camera, as well as how to monitor and control the observing environment to ensure a successful observing campaign for novices and experts alike.
Authors: D. James
Calibrating DECam data: the DECal and aTmCam calibration systems [1.38 MB PDF]
Jennifer Marshall
DECam has the potential to provide extremely high quality, high precision photometric measurements if the data are calibrated appropriately. Two calibration systems are now in use at CTIO that can be used to calibrate the spectral response of the DECam data. The DECal system is used ~once per month to measure and monitor the relative throughput of the telescope+DECam system as a function of wavelength and time. The aTmCam system autonomously monitors the atmospheric transmission of the site every night, producing a complete atmospheric transmission model ~once per hour. These two systems can be combined to produce photometric measurements with DECam having better than 1% precision.
Authors: Jennifer Marshall, Ting Li, Darren DePoy, David James
The DECam Community Pipeline [4.17 MB PDF]
Francisco Valdes
The DECam Community Pipeline (CP) provides calibrated science data products for all community programs through the NOAO Science Archive. This presentation describes the calibrations applied to produce the data products.
Authors: Francisco Valdes
The NOAO Science Archive - Present and Future [23.73 MB PDF]
Mark Dickinson
The NOAO Science Archive holds raw data from all NOAO telescopes and instruments, as well as pipeline-reduced data from its wide-field imagers, Mosaic, NEWFIRM and (now) DECam. It is the primary way for observers to retrieve their own data, and for other users to find valuable archival data after their proprietary periods end. Most recently, the Archive has started to incorporate and serve the reduced, calibrated data products from large DECam surveys, starting with the Year 1 data delivery from the Dark Energy Survey. I will describe the current state of the NOAO Science Archive, its likely future evolution, and its potential utility for DECam users everywhere.
Authors: Mark Dickinson
Dark Energy Survey Overview [2.43 MB PDF]
Christopher Miller
The Dark Energy Survey is using 525 nights on DECam over a 5-year period to image 5000 square degrees in 5 filters to a depth of ~24 in the r-band. I will present the current status and future plans for the survey and its footprint. I will also discuss the primary science drivers and the connections to other cosmological datasets. Finally, I will highlight new scientific results from Science Verification data.
Authors: Christopher J. Miller
Public Data Releases from the Dark Energy Survey [12.45 MB PDF]
Robert Gruendl
The Dark Energy Survey will image 5,000 square degrees in the South Galactic Cap in the grizY bands over 5 years along with a higher cadence survey of 10 supernova fields in the the griz bands. Now in the second year of the survey, the calibrated image products reduced by the DESDM pipelines at NCSA are becoming public and are available through the NOAO Science Archive. I will briefly describe the pipeline processing behind this first release, the planned improvements for future releases, and the data products being made available by the DES in this and future data releases.
Authors: Gruendl
What to Expect from DES Public Data [894 KB PDF]
Brian Yanny
The Dark Energy Survey (DES) has completed two years of data taking as of Feb 2015. In addition to all raw images becoming public one year after they are taken, DES Data Management (DESDM) is releasing detrended, calibrated single epoch exposures into the NOAO Science Archive each year. Finally, DES will have two public releases of reduced coadded exposures and fully searchable catalogs, currently scheduled for mid-year 2017 and 2020. We will discuss details of all these releases.
Authors: Brian Yanny
The Dark Energy Survey: results in Large Scale Structure from Science Verification data [4.59 MB PDF]
Ignacio Sevilla
The Dark Energy Survey (DES) is a 5000 square degree photometric survey with the goal of measuring the parameters of dark energy. In August 2013, it began survey operations using the DECam imager. Making measurements of Large Scale Structure using galaxy clustering is one of the primary science drivers of the experiment. When combined with other Dark Energy probes made with the same data, these measurements will enable either a strong validation of the current LCDM paradigm, or will show inconsistencies pointing towards a cosmology based on modified gravity or an evolving Dark Energy equation of state. Some of the more interesting results from this project will come not only from measuring the BAO scale, but also from obtaining the cross-correlation with the CMB signal, measuring the galaxy bias with high statistical precision and at multiple redshifts, and combining weak lensing and clustering measurements using the same dataset. In this contribution, we will describe ongoing efforts at making measurements using the initial Science Verification dataset (aproximately 150 square degrees) with special focus on understanding the systematics that will be important for later releases.
Authors: Ignacio Sevilla for the Dark Energy Survey Collaboration
The DECam Legacy Survey: A Progress Report [10.02 MB PDF]
Arjun Dey
I will present a progress report on the Dark Energy Camera Legacy Survey, describing the goals, current status, and lessons learned.
Authors: Arjun Dey + DECaLS Team
DECam NEO: A sensitive, wide-field search for near-Earth objects [9.03 MB PDF]
Lori Allen
Near Earth Objects (NEOs) are asteroids or comets whose perihelion distance is less than 1.3 AU. Current estimates suggest that large NEOs (diameter 140m or more) impact the earth every few thousand years on average. Smaller asteroids (30m-50m) are believed to impact the earth with an average frequency of ~100 years, but this estimate is highly uncertain, based in part on an incomplete understanding of the size distribution of NEOs below 100m. Until now, it has not been possible to measure the size distribution of these objects, because large-aperture telescopes have not been equipped with very wide-field imagers. Now, the large étendue of DECam+Blanco allows us to probe a previously unexplored region of NEO parameter space and therefore hazard space. We have recently initiated a 30-night survey with DECam, with the goal to measure the size distribution of NEOs below 100m. Here we report on preliminary results based on the first 10 nights of our survey.
Authors: L. Allen, F. Valdes, D. Trilling, D. James, D. Herrera, C. Fuentes, T. Axelrod, J. Rajagopal, M. Brown
The High cadence Transient Survey (HiTS): real-time detection of supernovae and other transients with DECam [5.57 MB PDF]
Francisco Forster
At the Center for Mathematical Modelling (CMM) of the University of Chile and the Millennium Institute for Astronomy (MAS) we have developed a novel transient detection pipeline to be used in real-time with data from the Dark Energy Camera (DECam). During five contiguous nights in the first week of March of 2014 we were able to achieve the real-time data analysis of more than 120 square degrees of the sky with a cadence of only two hours and a processing time of less than one exposure time for every image. We processed more than 400 billion pixels in total, leading to the discovery of 12 newly exploding SNe in almost real-time. We found thousands of previously unknown asteroids and hundreds of variable stars that can be used to map the structure of the outer parts of the Milky Way. In this talk I will discuss the survey design and the current status of the project, as well as some of the new tools we have developed for real time transient detection applications.
Authors: Forster, F; Maureira, J.C.; San Martin, J.; Cabrera, G.; Hamuy, M; Gonzalez-Gaitan, S.; Galbany. Ll.;Anderson, J.; de Jaeger, Th.; Bufano, M.; Kunkarayakti, H.; Hsiao, E.; Pignata, G.; Vera, E.; Smith. R.C.; Morrel, N.; Lira. P.; and PESSTO collaboration
Near-Earth Object Discovery Confirmation with DECam
Sarah Sonnett
Near-Earth Objects (NEOs) are asteroids or comets with perihelia < 1.3 AU. Discovering NEOs and determining their orbits and sizes is needed to assess the risk of an impact or explosion. NEO studies also enable detailed investigations of inner solar system objects and the processes that govern their physical and dynamical evolution. The NEOWISE space mission is currently discovering NEOs in the infrared, so that when paired with optical follow-up from the ground, precise orbits, albedos, and thermal inertia values can be calculated. We have secured a small amount of this follow-up time on DECam. Because many of our discoveries are best observed in the southern hemisphere, are very faint (V ~ 22.5), and have typically large position uncertainty maps, DECam has played a critical role in recovering our NEO discoveries. We will review our discovery and follow-up process as well as some of the science highlights from NEOs confirmed through our program.
Authors: S. Sonnett (JPL/CalTech), A. Mainzer (JPL/CalTech), J. Bauer (JPL/CalTech), T. Grav (Planetary Science Institute), J. Masiero (JPL/CalTech), C. Nugent (JPL/CalTech), E. Kramer (JPL/CalTech)
SMASH - Techniques and Science [15.78 MB PDF]
Knut Olsen
Recent work on the Magellanic Clouds has led to surprising new views of these iconic galaxies. We now know that their stellar populations extend over a vast area of sky, that they may be bound only loosely to the Milky Way, and that their mutual interaction has likely created a complex array of both gaseous and stellar tidal debris. The Survey of the MAgellanic Stellar History (SMASH) will map the structure of the Clouds and their environs with unprecedented fidelity. SMASH is imaging 480 square degrees of the southern sky with DECam, covering a ~2400 square degree area at 20% filling factor. With its depth of 24th mag in gri (and ~23 in uz), SMASH will (a) search for the stellar components of the Magellanic Stream and Leading Arm, (b) detect and map the extended smooth components and substructure of the Magellanic Clouds, and (c) derive spatially resolved, precise star formation histories out to large radii. Our first year of data reveal (1) Large Magellanic Cloud (LMC) stellar populations extending out to a radius of at least 19 deg (~17 kpc) in several directions, (2) clear signatures of two dominant LMC star formation episodes at intermediate radii as revealed by multiple subgiant branches, and (3) evidence for an expansive stellar substructure in the Milky Way halo at a distance of ~30 kpc.
Authors: Knut A. Olsen, David Nidever, Robert A. Gruendl, Gurtina Besla, Abi Saha, Edward Olszewski, Ricardo Munoz, Carme Gallart, Matteo Monelli, Alistair R. Walker, Robert D. Blum, Catherine C. Kaleida, Kathy Vivas, Steven R. Majewski, Dennis F. Zaritsky, Roeland P. Van Der Marel, Eric F. Bell, Blair Conn, Guy S. Stringfellow, Shoko Jin, Lara Monteagudo Nervion, Maria-Rosa Cioni, Noelia Noel, Nicolas Martin, Antonela Monachesi, Thomas de Boer, You-Hua Chu, Hwihyun Kim, David Martinez-Delgado, Lent C. Johnson, Andrea Kunder
The Search for Light Echoes of Historic SNe in the Southern Hemisphere with DECam [13.22 MB PDF]
Armin Rest
In recent years, light echoes of ancient SNe have been discovered with the Mosaic II cameras at the CTIO Blanco and KPNO Mayall telescopes. We have found light echoes in the LMC (Rest et al. 2005, 2008a) and near the historical Galactic events Cas A, Tycho, and Eta Car (Rest et al. 2008b, 2011a, 2012). However, searches for light echoes near the Kepler SN and SN 1006 have not yet been successful. We have started a search for light echoes in the southern hemisphere using DECam at the CTIO Blanco telescope. DECam is an excellent light echo detection system with its larger field of view and much faster read time compared to Mosaic II. This increases the efficiency of the search by more than a factor of 10, allowing us to cover significantly larger areas of the sky. We report on strategy, progress, current coverage, and first results of our project.
Authors: Rest, A. (STScI), Bianco, F. (NYU), Chornock, R. (Ohio U.), Clocchiatti, A. (U. de Catolica), Foley, R. J. (UIUC), James, D. (CTIO), Matheson, T. (NOAO), Narayan, G. (NOAO), Olsen, K. A. (NOAO), Points, S. (CTIO), Prieto, J. L. (U. D. Portales), Smith, R. C. (CTIO), Smith, N. (U. of Arizona), Suntzeff, N. B. (Texas A&M)), Welch, D. L. (McMaster U.), Zenteno, A. (CTIO)
Exploring Milky Way Halo Substructures from Large-Area Digital Sky [1.87 MB PDF]
Ting Li
Over the last two decades, large-area digital sky surveys have provided deep photometric catalogs of stars in our Galaxy. The ability to detect and characterize substructures in our halo has increased dramatically. These substructures show that the Milky Way Galaxy is a complex and dynamic structure that is still being shaped by the accretion and merging of neighboring smaller galaxies. Sharma et al. (2010) developed a density-based hierarchical group-finding algorithm to identify stellar halo substructures in a catalog of M-giants from the Two Micron All Sky Survey (2MASS). This algorithm uncovered 16 substructures in the Milky Way halo, six of which were unknown at the time. In this talk, I will discuss the spectroscopic follow-up observations of one of the six substructure candidates. The radial velocities and the metailicities derived from the spectra show that the stars selected have kinematic and abundance signatures consistent with a disrupted merger remnant in the Galactic potential. I will also briefly discuss the application of this group-finding algorithm on a catalog of main-sequence turnoff (MSTO) stars from the Dark Energy Survey, which are more sensitive to low-luminosity events than the 2MASS M-giant sample. With higher photometric precision at the faint magnitude limit, more substructures could potentially be revealed with the future photometric surveys and provide a complete census of our Galaxy’s recent accretion history.
Authors: Ting Li, Jennifer Marshall, Kathryn Johnston, Allyson Sheffield
The Detailed Substructure of the Milky Way Stellar Streams: DECam Imaging of the Eastern Banded Structure [3.97 MB PDF]
Jonathan Hargis
Observational studies of the Milky Way's halo substructure are an integral part of understanding galaxy formation in a cosmological context. For example, the numerous stellar streams of our Galaxy have provided direct evidence of the hierarchical nature of galaxy assembly. Their detailed study reveals the nature of the Milky Way's recent progenitors, and their morphologies may contain the observational signatures of numerous low mass dark subhalos predicted by LCDM theory. I will present an overview and some initial results of our DECam imaging program to map one of the nearest stellar streams, the Eastern Banded Structure (EBS; d~10 kpc), as well as its possible progenitor. Our imaging has a limiting magnitude approximately two magnitudes deeper than SDSS, nearly five magnitudes below the main sequence turnoff. In addition, our imaging studies serve as precursor LSST science, providing a rich data set for understanding how low surface brightness structures at faint magnitudes can be quantified in the era of LSST.
Authors: Jonathan R. Hargis, B. Willman (Haverford College), D. Sand (Texas Tech University), J. Strader (Michigan State University), J. H. Yoon (Univ of California Santa Barbara), R. Fadely (New York University), Carl Grillmair (Caltech/IPAC)
“Rich Field Photometry - Techniques and Science" [4.42 MB PDF]
Abhijit Saha
I will discuss issues related to stellar photometry in very crowded fields, and the use of a priori criteria that can be used to identify false detections and measurements. I will talk about implementation of a working "pipeline" style photometry process, and bringing these methods to bear on a synoptic study of select fields in the Galactic Bulge, using DECam. Some early results from this study will be shown: how multiband photometry of RR Lyraes is being used to produce reddening corrected color-magnitude diagrams of the bulge region with the aim of disambiguating disk and spheroid populations.
Authors: A. Saha
DECam Variability Surveys of the Galactic Bulge Survey Fields [4.57 MB PDF]
Robert Hynes
The Chandra Galactic Bulge Survey (GBS) is a shallow but wide multi-wavelength survey of X-ray sources along the line-of-sight to the inner Galactic Bulge, covering 12 square degrees above and below the plane. The depth is chosen to maximize the yield of quiescent X-ray binaries relative to less luminous X-ray sources, and the latitude to minimize extinction while giving up as little as possible of the Bulge source density. The GBS has identified 1640 X-ray sources, expected to be comprised primarily of X-ray binaries, cataclysmic variables, and active stars, with smaller populations such as nearby lower activity stars, protostars, massive stars, and background active galaxies. Most of the expected sources should have variable optical/IR counterparts, so wide-field optical and near-IR variability studies are ideal for identifying these counterparts in crowded Bulge fields. I will describe the central role being played by variability surveys within the GBS project. In particular I will highlight the tremendous power of DECam in efficiently producing massively multiplexed, high-cadence lightcurves of GBS sources.
Authors: Hynes, R.I., Johnson, C.B., Britt, C.T., Jonker, P.G., Torres, M.A.P., Maccarone, T.J., Steeghs, D., Greiss, S., Wu, J., Nelemans, G., Heinke, C., and The GBS Collaboration
Substellar Mass Objects in the Belt of Orion - What DECam Does for Us [7.14 MB PDF]
Frederick Walter
OB associations are ideal sites for probing the formation of low mass objects. Our "wide-field" near-IR (JHK) survey of ~18 sq deg in the Orion OB1a and OB1b associations using the CPAPIR camera on the SMARTS/CTIO 1.5m telescope revealed thousands of potential substellar mass members of this nearby OB association. Unfortunately, JHK colors do not discriminate well between foreground M dwarfs and 1-2 Myr-old substellar mass objects, which are expected to have late-M spectral types, so foreground contamination could be a significant problem.
In December we used 2 nights with DECam to obtain deep grizY images of 12 fields in and near the belt of Orion.
The purpose is to obtain optical colors of our candidates and fainter objects. The optical colors are very good discriminants between the M and early L spectral type objects. We intended to reach the planetary mass limit,
but were given bright sky (20-30 degrees from the full moon).
I will present an overview of the program to date, a summary of the DECam data (and how I'm using IDL to deal with 900 GB of fpacked data). In return, I will ask how to do a good photometric calibration of these images.
Authors: Frederick M Walter & Jacqueline K Faherty
Variable Stars in the Sextans Dwarf Spheroidal Galaxy [3.3 MB PDF]
Kathy Vivas
Pulsating stars below the horizontal branch (aka, dwarf cepheids) provide an interesting tool to study the stellar populations and structure of dSph galaxies since stars coming from different evolutionary paths may coexist in the region of the instability strip. The detection of these variables is challenging in distant systems because of their faint brightness and very short pulsation periods. We present preliminary results of a DECam project aimed to unveil the population of faint variables in the Sextans dSph galaxy.
Authors: Kathy Vivas (CTIO), Mario Mateo (University of Michigan), Javier Alonso-García (PUC, Chile), Alistair Walker (CTIO), David Nidever (University of Michigan)
Wide-Field Photometric Survey of Young Southern Open Clusters [830 KB PDF]
Jeffrey Cummings
Star clusters are an observational foundation for stellar astrophysics, provide essential information for the study of Galactic structure and evolution, and are invaluable environments for analysis of stellar and chemical evolution.
There are few fields in astrophysics that do not in some way rely on results derived from open cluster analysis. Our project is a uniform study of young southern open clusters using DECam. We have obtained ugriz photometry of 12 carefully chosen nearby and rich clusters, where their full extent, if not the entire cluster, have previously only been poorly studied. DECam for the first time has allowed efficient and deep observation these large clusters within a single field of view. Given their young ages (ranging from 25 to 350 Myr), deep and wide-field photometry of this sample of clusters will form a strong foundation to address three outstanding astrophysical questions: 1.) What is the initial mass function (IMF) of stars and does it vary? 2.) What types of mixing and diffusion may be taking place in stellar interiors, and how do they vary with mass and metallicity? 3.) What is the threshold mass separating white dwarf formation from Type II supernovae?
Authors: Jeffrey Cummings, Douglas Geisler, Jason Kalirai, P.-E. Tremblay, F. Mauro, C. Deliyannis
Tracing Galaxy Group Assembly through Fossil Tidal Features [22.59 MB PDF]
Iraklis Konstantopoulos
Over cosmic time galaxies evolve from young, blue disks to old, red spheroids. The density of their environment plays a major role (Dressler et al., 1980, ApJ, 236, 351), hence studies have so far focussed on galaxy clusters. There, galaxies interact with multiple partners in quick succession and thus age faster than their isolated counterparts. However, the large membership of clusters results in the simultaneous action of various physical processes, therefore hindering the identification of those mechanisms that dominate galaxy evolution. Furthermore, populous clusters represent just 2% of the stellar mass in the present-day universe (Eke et al., 2005, MNRAS, 362, 1233), with looser groupings dominating in local redshift surveys (e.g., Small et al., 1999, ApJ, 524, 31).
Enter compact galaxy groups (CGs). With similar densities as clusters but few members they enable an intimate understanding of every galaxy and the physical processes at play. During semesters 2014A and B we deeply imaged eight CGs with DECam in three bands (and an additional group in one band), with the aim of tracing their assembly history. These data are deep enough, and of high-enough image quality, to serve as a legacy dataset in the pre-LSST-era, and will remain state-of-the-art for the next decade. For our science, they present an important step toward understanding whether CGs are a class of grouping that could occur at any redshift, or a privilege of the cosmological current era. With analysis now underway, preliminary results reveal tidal features in all nine groups in our sample, although one group shows no linkages between galaxies, just extensions to individual galaxy disks. This group, HCG7, has in the past been suggested as a first-infall group, one that is coming together right now, at redshift zero. I will examine this tantalising prospect and review our work toward untangling the assembly histories of the nine groups through age-dating their tidal debris and various ancillary information. Finally, I will present ideas and solicit input for methods through which the legacy value of these wide-field images can be realised.
Authors: Iraklis Konstantopoulos, Jane Charlton, Michael Rodruck, David James, Dane Kleiner
Lyman-Alpha Galaxies at the End of Reionization with DECam [4.06 MB PDF]
Zhenya Zheng
Lyα photons from galaxies are resonantly scattered by neutral inter-galactic medium (IGM), leading to an apparent decline in the luminosity function of Lyα galaxies. Our group pioneered the use of Lyα emitters to show that the IGM is ionized at z = 6.5 (Malhotra & Rhoads 2004). Several small surveys since then indicate weakening of the Lyα galaxies at z ∼ 7, implying a rapid reionization between z=7 and z=6.5. However, due to the limited survey area, very few LAEs are confirmed at z >~ 7. To take the convenience of large FOV and good performance of DECam, we are building a narrowband filter at 9700A for DECam, to effectively hunt for LAEs at z=7. In this talk, we will introduce our DECam narrowband survey, compare it with current z>~7 narrowband surveys, and present how the DECam NB survey result will constrain the ionization fraction of our Universe at z=7. Basically, we expect to detect several hundred Lya galaxies at z~7, and find the neutral fraction of our Universe through both Lya Luminosity function and Clustering, as well as the Lya line profile in the followup spectroscopic work. Our survey may also be effective to find high-z quasars, Lyman break galaxies and low-z emission line galaxies, which will help to determine the faint end (for LBG and ELG) and bright end (for quasar) of their luminosity function.
Authors: Zhenya Zheng, James Rhoads, Junxian Wang, Sangeeta Malhotra, Leopoldo Infante
Observing the electromagnetic counterparts of gravitational wave events with DECam: opportunities and potential impact
Marcelle Soares-Santos
First detections of coalescing neutron star binaries by a dedicated network of gravitational wave detectors are widely expected to happen within this decade. This long sought groundbreaking achievement will inaugurate new avenues for astrophysical studies. As discussed in this talk, DECam is in position to play a crucial role in that scenario. I describe plans to use DECam to followup gravitational wave events in search for their electromagnetic counterparts in optical bandpasses. Such hypothesized counterparts are supernova-like events resulting from the decay of neutron-rich radioactive species synthesized during the merger. They are faint, red, and fast decaying transients which impose an observational challenge for followup programs. In addition, early gravitational wave detectors provide poor sky localization for their candidate events, resulting in search regions of tens of square degrees. With a 3 square degree field of view, a 4 meter telescope, and specially red-sensitive CCDs, DECam is the ideal instrument to meet those challenges. It is also unique in the southern hemisphere. First coordinated detection of electromagnetic and gravitational radiation from merger events are a thrilling prospect for the DECam community.
Authors: Marcelle Soares-Santos
Measuring the Free-Floating Planet Mass Function with DECam and K2 [6.9 MB PDF]
Matthew Penny
The distribution of mass in free-floating planets holds vital information on the formation and subsequent evolution of the planetary systems from which they were ejected.
In the spring of 2016 the ninth campaign of K2 (the extended, two-wheel Kepler mission) will be targeted towards the Galactic bulge, where it will perform the first wide-field, space-based microlensing survey. This ~5 square degree survey will discover tens of free-floating planets by itself, but its real value will come from simultaneous ground-based observations that will provide parallax measurements. However, in order to convert these parallaxes into the first ever free-floating planet mass measurements, it is necessary to survey from the ground in more than one color at high cadence. The current dedicated microlensing survey telescopes do not have sufficient etendue to achieve the necessary depth and cadence to enable these mass measurements, but with 20x the etendue of the OGLE microlensing telescope DECam does.
The K2 microlensing survey will only happen once, and so the upcoming opportunity is the only chance we will have to measure the masses of enough free-floating planets to characterize their mass function. DECam is the only instrument in the world that can ensure this measurement is made.
The 6-square-degree, 80-night survey required to measure the free-floating planet mass function would also be a boon to other fields. The K2-DECam fields lie on the ecliptic so would enable an extremely deep search for objects like Sedna and 2012 VP113 in the inner Oort cloud, and from the survey data alone allow their orbits, colors and spin rates to be measured. The multicolor high-cadence monitoring would also enable a survey of more than 10^5 M-dwarfs to measure the energy distribution of large flares that could have a large impact on the habitability of planets orbiting the majority of the Galaxy's stars.
Authors: Matthew Penny
Probabilistic photometric redshift in the era of petascale astronomy [6.39 MB PDF]
Matias Carrasco Kind
Photometric redshifts (photo-z) are quickly becoming a critical measurement for large photometric galaxy surveys and there has been a significant development in this area in the last decade. Given the enormous amount of imaging data we are expecting to be available in the upcoming years, there is a need for fast, robust and more complex algorithms to compute and store not only a photo-z single estimate but also its probability density function.
In this talk I will review some of the state-of-the-art machine learning and data mining algorithms to compute, combine and store photo-z PDFs for large galaxy surveys. I will discuss how, a supervised machine learning technique , a unsupervised technique and a standard template fitting approach can be combined together in a Bayesian framework to improve the accuracy of the photo-z PDF as well as reducing the fraction of outliers in a completely new approach. I will also discuss how we can reduce the amount of storage of individual PDFs by using sparse representation techniques with a compression rate of 90% with an reconstruction accuracy of 99.8% using only 10 to 20 4-byte integers per galaxy which will allow us to store several techniques in a reduced amount of space which is becoming critical for current photometric surveys as several hundred million objects are expected. I will finalize by showing recent progress on how to implement and access these photo-z PDF from a SQL database using advance techniques allowing us for the first time to deal with these objects directly from the database and in fast and efficient manner with no precedents. The focus of this talk would be more into how we have integrated new functions and types to handle photo-z PDF into the DESDM Database and how this can be the foundation of including scientific scripting in SQL format making use of the DB resources.
Authors: Matias Carrasco Kind + DESDM NCSA team