This award will provide funds for two groups to participate in the planning for the Large Synoptic Survey Telescope (LSST). The LSST is a facility under consideration that will address the nature of Dark Matter and Dark Energy which are observed to be fundamental components of the Universe that do not fit within the otherwise stunningly successful Standard Model of particle physics. LSST will address these issues in a uniquely powerful way and is planned to be the most ambitious sky survey in the visible band. It will be a large, wide-field, ground-based system designed to obtain multiple images covering the sky. The survey will feature precision astrometry and photometry and thus will be ideal for measurements of weak lensing and the construction of transient object light curves which is ideal for Supernovae Ia cosmology.
The PIs are members of the LSST project and besides their work on the LSST calibration system they are also members of the LSST Supernova and Large Scale Structure Science collaborations. They are working on a simulation of the LSST calibration to define parameters for design and construction, and during the time frame of this award this work will transition to implementation of a calibration pipeline which will be tested on both simulated LSST raw data and real sky data.
There are several broader impacts of this activity. At Wayne State, undergraduates are included in research via an REU/RET program. At Cincinnati, there is an active QuarkNet program which involves K-12 teachers in research and develops content that they include in their class rooms.
The University of Cincinnati (UC) group was directed by two PI's, Michael Sokoloff (MS) and Brian Meadows (BM). Also in the group there have been two students (Bogdan Popescu, and Randa Asad) who have graduated with PhD's in astrophysics. A third graduate student (Adam Davis) began work with us, but chose to move on to work on the LHCb experiment at CERN. Zachary Huard, a postdoctoral fellow, worked in this group for a year. The UC group collaborated with other US scientists from Wayne State University, University of Washington, SLAC National Accelerator Laboratory, Harvard University and Brookhaven National Laboratory in the design of the photometric calibration system for the Large Synoptic Survey Telescope to be built at Cerro Pachón, an 8,800-foot mountain peak in northern Chile. The 8 m LSST will be able to cover the entire Southern sky once, on average, every three nights - an unprecented rate. The superior optical design of the LSST is well matched to the world's largest telescope camera with three billion CCD pixels. The exceptional sensitivity will make observation of galaxies at distances probing the far reaches of the universe. The LSST has been rated by the 2010 decadal survey panel as the most important ground based survey, and a wide variety of scientific studies are possible with such a facility. Our interest at UC is in attempting to probe the distribution of dark matter in the universe. Little is known about dark matter (DM) and its identity is a complete mystery. It emits no light of its own, but it can be observed through its gravitational interaction with ordinary matter and with light. Light from distant galaxies can be gravitationally deflected by any DM that exists between the galaxy and an Earth observer. This "weak lensing" results in distortion of the galaxy image observed. Elliptical stretching of a cluster of galaxies observed from the Earth can be interpreted in terms of the amount of intervening DM, and a map of the DM distribution in the universe can, in principal, be made. Such a map would be an invaluable source of information of the evolution of the universe and provide a clue to the nature of DM and of dark energy. Scientific requirements on the LSST performance are demanding. Clearly, exceptional astrometric precision is necessary for weak lensing measurements. Photometric precision is also essential so that distance scales can be precisely determined, and overlapping images resolved. The UC group has worked in the LSST photometric calibration group. We joined at the time it had been decided that three sources of data would be required. These are individual star images from the LSST; spectra from "standard stars" obtained using an auxiliary telescope; and data from LSST exposed to a flat, uniformly illuminated disc. The UC group worked on the first two of these. First, the LSST operation will guarantee an immense set of multiple images of main sequence stars. Basic properties (magnitude or spectral distribution) of any star will be virtually unchanged between visits, but the observations may differ due to variations in, for example, mirror reflectivity, amplifier gain, atmospheric transmission, etc.. The purpose of the calibration process is to provide a way to track these effects. The visit-to-visit stability of the stars provides the means to do this. The UC group provided the first simulation of the LSST operation to generate basic star data that could be used to test the algorithms involved. The second source of calibration data will come from a high resolution spectrometer mounted on an auxiliary telescope aimed at a number of standard stars (main sequence stars or white dwarfs whose spectra are well known). In any one LSST pointing, very few such stars will appear and the spectral range will only be delineated in broad ranges by a set of 7 fliters. A comparison between observed and expected spectral response can be used to build models of the transmission of Earth's atmosphere as a function of direction and time. UC has contributed a study of the way to build such models. A flat disc ("Dome Flat"), uniformly illuminated by a tunable laser is the third component in the LSST calibration. This will provide a means to factor out the throughput of the LSST itself. It can be placed in or near the LSST aperture at times, to be decided, when normal exposures are halted. These might be when filters are changed or, perhaps, during the daytime. This grant has made it possible for a group of particle experimentalists to play a role in the design of a world class observational cosmology project. The two students who earned PhD's have each moved on to other positions in astrophysics. The postdoctoral fellow and the two PI's have learned much about a new field.
