Browsing by Author "Ivezic, Zeljko"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    The LSST DESC DC2 Simulated Sky Survey
    (2021) Abolfathi, Bela; Alonso, David; Armstrong, Robert; Aubourg, Eric; Awan, Humna; Babuji, Yadu N.; Bauer, Franz Erik; Bean, Rachel; Beckett, George; Biswas, Rahul; Bogart, Joanne R.; Boutigny, Dominique; Chard, Kyle; Chiang, James; Claver, Chuck F.; Cohen-Tanugi, Johann; Combet, Celine; Connolly, Andrew J.; Daniel, Scott F.; Digel, Seth W.; Drlica-Wagner, Alex; Dubois, Richard; Gangler, Emmanuel; Gawiser, Eric; Glanzman, Thomas; Gris, Phillipe; Habib, Salman; Hearin, Andrew P.; Heitmann, Katrin; Hernandez, Fabio; Hlozek, Renee; Hollowed, Joseph; Ishak, Mustapha; Ivezic, Zeljko; Jarvis, Mike; Jha, Saurabh W.; Kahn, Steven M.; Kalmbach, J. Bryce; Kelly, Heather M.; Kovacs, Eve; Korytov, Danila; Krughoff, K. Simon; Lage, Craig S.; Lanusse, Francois; Larsen, Patricia; Le Guillou, Laurent; Li, Nan; Longley, Emily Phillips; Lupton, Robert H.; Mandelbaum, Rachel; Mao, Yao-Yuan; Marshall, Phil; Meyers, Joshua E.; Moniez, Marc; Morrison, Christopher B.; Nomerotski, Andrei; O'Connor, Paul; Park, HyeYun; Park, Ji Won; Peloton, Julien; Perrefort, Daniel; Perry, James; Plaszczynski, Stephane; Pope, Adrian; Rasmussen, Andrew; Reil, Kevin; Roodman, Aaron J.; Rykoff, Eli S.; Sanchez, F. Javier; Schmidt, Samuel J.; Scolnic, Daniel; Stubbs, Christopher W.; Tyson, J. Anthony; Uram, Thomas D.; Villarreal, Antonio; Walter, Christopher W.; Wiesner, Matthew P.; Wood-Vasey, W. Michael; Zuntz, Joe
    We describe the simulated sky survey underlying the second data challenge (DC2) carried out in preparation for analysis of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) by the LSST Dark Energy Science Collaboration (LSST DESC). Significant connections across multiple science domains will be a hallmark of LSST; the DC2 program represents a unique modeling effort that stresses this interconnectivity in a way that has not been attempted before. This effort encompasses a full end-to-end approach: starting from a large N-body simulation, through setting up LSST-like observations including realistic cadences, through image simulations, and finally processing with Rubin's LSST Science Pipelines. This last step ensures that we generate data products resembling those to be delivered by the Rubin Observatory as closely as is currently possible. The simulated DC2 sky survey covers six optical bands in a wide-fast-deep area of approximately 300 deg(2), as well as a deep drilling field of approximately 1 deg(2). We simulate 5 yr of the planned 10 yr survey. The DC2 sky survey has multiple purposes. First, the LSST DESC working groups can use the data set to develop a range of DESC analysis pipelines to prepare for the advent of actual data. Second, it serves as a realistic test bed for the image processing software under development for LSST by the Rubin Observatory. In particular, simulated data provide a controlled way to investigate certain image-level systematic effects. Finally, the DC2 sky survey enables the exploration of new scientific ideas in both static and time domain cosmology.
  • No Thumbnail Available
    Item
    Variable faint optical sources discovered by comparing the POSS and SDSS catalogs
    (2006) Sesar, Branimir; Svilkovic, Domjan; Ivezic, Zeljko; Lupton, Robert H.; Munn, Jeffrey A.; Finkbeiner, Douglas; Steinhardt, William; Siverd, Rob; Johnston, David E.; Knapp, Gillian R.; Gunn, James E.; Rockosi, Constance M.; Schlegel, David; Vanden Berk, Daniel E.; Hall, Pat; Schneider, Donald P.; Brunner, Robert J.
    We present a study of variable faint optical sources discovered by comparing the Sloan Digital Sky Survey (SDSS) and the Palomar Observatory Sky Survey (POSS) catalogs. We use SDSS measurements to photometrically recalibrate several publicly available POSS catalogs (USNO-A2.0, USNO-B1.0, DPOSS [the Digitized Second Palomar Observatory Sky Survey], and GSC2.2 [the Guide Star Catalog 2.2]). A piecewise recalibration of the POSS data in 100 arcmin(2) patches (one SDSS field) generally results in an improvement of photometric accuracy (rms) by nearly a factor of 2, compared to the original data. In addition to the smaller core width of the error distribution, the tails of the distribution become much steeper after the recalibration. These improvements are mostly due to the very dense grid of calibration stars provided by SDSS, which rectifies the intrinsic inhomogeneities of Schmidt plates. We find that the POSS I magnitudes can be improved to similar to 0.15 mag accuracy, and POSS II magnitudes to similar to 0.10 mag accuracy. The smallest final errors are obtained with the GSC2.2 catalog, for which they approach 0.07 mag at the bright end. We use the recalibrated catalogs for the similar to 3300 deg(2) of sky in the SDSS Data Release 2 to construct a catalog of similar to 60,000 sources that are variable on timescales of 10-50 yr, and make it publicly available. Using this catalog, we find that at least 1% of faint optical sources appear variable at the > 0.25 mag level, and that about 20% of the variable population are quasars, although they represent only 0.6% of all point sources in the adopted flux-limited sample (g < 19). A series of statistical tests based on the morphology of SDSS color-magnitude and color-color diagrams, as well as visual comparison of images and comparison with repeated SDSS observations, demonstrate the robustness of the selection methods: three out of four candidate variable sources are correctly recognized to vary. We also demonstrate that candidate RR Lyrae stars trace the same halo structures, such as the Sgr dwarf tidal stream, that were discovered using repeated SDSS observations. We utilize the POSS-SDSS selected candidates to constrain the halo structure in the parts of sky for which repeated SDSS observations do not exist. We quantify the distribution of variable sources in the SDSS color-color diagrams and the variability characteristics of quasars. The observed long-term quasar variability ( structure function) is smaller than predicted by the extrapolation of the power law measured for short timescales using repeated SDSS imaging (0.35 vs. 0.60 mag for SDSS-POSS I and 0.24 vs. 0.35 mag for SDSS-POSS II, rms). This turnover in structure function suggests that the characteristic timescale for quasar variability is on the order of 1 yr in the rest frame.