Yusra AlSayyad

THE IDENTIFICATION OF z -DROPOUTS IN PAN-STARRS1: THREE QUASARS AT 6.5< z < 6.7

Luminous distant quasars are unique probes of the high redshift intergalactic medium (IGM) and of the growth of massive galaxies and black holes in the early universe. Absorption due to neutral Hydrogen in the IGM makes quasars beyond a redshift of z~6.5 very faint in the optical

The SDSS–2MASS–WISE 10-dimensional stellar colour locus

z

Spurious shear in weak lensing with the large synoptic survey telescope

-band, thus locating quasars at higher redshifts require large surveys that are sensitive above 1 micron. We report the discovery of three new z>6.5 quasars, corresponding to an age of the universe of 6.5 quasars from 4 to 7. The quasars have redshifts of z=6.50, 6.52, and 6.66, and include the brightest z-dropout quasar reported to date, PSO J036.5078+03.0498 with M_1450=-27.4. We obtained near-infrared spectroscopy for the quasars and from the MgII line we estimate that the central black holes have masses between 5x10^8 and 4x10^9 M_sun, and are accreting close to the Eddington limit (L_Bol/L_Edd=0.13-1.2). We investigate the ionized regions around the quasars and find near zone radii of R_NZ=1.5-5.2 proper Mpc, confirming the trend of decreasing near zone sizes with increasing redshift found for quasars at 5.7<z<6.4. By combining R_NZ of the PS1 quasars with those of 5.7<z<7.1 quasars in the literature, we derive a luminosity corrected redshift evolution of R_NZ,corrected=(7.2+/-0.2)-(6.1+/-0.7)x(z-6) Mpc. However, the large spread in R_NZ in the new quasars implies a wide range in quasar ages and/or a large variation in the neutral Hydrogen fraction along different lines of sight.

EFFECT OF MEASUREMENT ERRORS ON PREDICTED COSMOLOGICAL CONSTRAINTS FROM SHEAR PEAK STATISTICS WITH LARGE SYNOPTIC SURVEY TELESCOPE

We present the fiducial main sequence stellar locus traced by 10 photometric colors observed by SDSS, 2MASS, and WISE. Median colors are determined using 1,052,793 stars with rband extinction less than 0.125. We use this locus to measure the dust extinction curve relative to the r-band, which is consistent with previous measurements in the SDSS and 2MASS bands. The WISE band extinction coefficients are larger than predicted by standard extinction models. Using 13 lines of sight, we find variations in the extinction curve in H, Ks, and WISE bandpasses. Relative extinction decreases towards Galactic anti-center, in agreement with prior studies. Relative extinction increases with Galactic latitude, in contrast to previous observations. This indicates a universal mid-IR extinction law does not exist due to variations in dust grain size and chemistry with Galactocentric position. A preliminary search for outliers due to warm circumstellar dust is also presented, using stars with high signal-to-noise in the W3-band. We find 199 such outliers, identified by excess emission in Ks W3. Inspection of SDSS images for these outliers reveals a large number of contaminants due to nearby galaxies. Six sources appear to be genuine dust candidates, yielding a fraction of systems with infrared excess of 0:12 0:05%.

A MULTI-SURVEY APPROACH TO WHITE DWARF DISCOVERY

The complete 10-year survey from the Large Synoptic Survey Telescope (LSST) will image {approx} 20,000 square degrees of sky in six filter bands every few nights, bringing the final survey depth to r {approx} 27.5, with over 4 billion well measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high fidelity ray-tracing simulations. We identify and isolate the different sources of algorithm-independent, additive systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing analysis techniques. We find that the main source of the errors comes from an inability to adequately characterise the atmospheric point spread function (PSF) due to its high frequency spatial variation on angular scales smaller than {approx} 10{prime} in the single short exposures, which propagates into a spurious shear correlation function at the 10{sup -4}-10{sup -3} level on these scales. With the large multi-epoch dataset that will be acquired by LSST, the stochastic errors average out, bringing the final spurious shear correlation function to a level very close to the statistical errors. Our results imply that the cosmological constraints from LSST will not be severely limited by these algorithm-independent, additive systematic effects.

MODERATE C IV ABSORBER SYSTEMS REQUIRE 1012 M ☉ DARK MATTER HALOS AT z ∼ 2.3: A CROSS-CORRELATION STUDY OF C IV ABSORBER SYSTEMS AND QUASARS IN SDSS-III BOSS DR9

We study the effect of galaxy shape measurement errors on predicted cosmological constraints from the statistics of shear peak counts with the Large Synoptic Survey Telescope (LSST). We use the LSST Image Simulator in combination with cosmological N-body simulations to model realistic shear maps for different cosmological models. We include both galaxy shape noise and, for the first time, measurement errors on galaxy shapes. We find that the measurement errors considered have relatively little impact on the constraining power of shear peak counts for LSST.

Comparative evaluation of big-data systems on scientific image analytics workloads

By selecting astrometric and photometric data from the Sloan Digital Sky Survey (SDSS), the Lepine & Shara Proper Motion North Catalog (LSPM-North), the Two Micron All Sky Survey (2MASS), and the USNO-B1.0 catalog, we use a succession of methods to isolate white dwarf (WD) candidates for follow-up spectroscopy. Our methods include reduced proper motion diagram cuts, color cuts, and atmospheric model adherence. We present spectroscopy of 26 WDs obtained from the CTIO 4 m and APO 3.5 m telescopes. Additionally, we confirm 28 WDs with spectra available in the SDSS DR7 database but unpublished elsewhere, presenting a total of 54 WDs. We label one of these as a recovered WD while the remaining 53 are new discoveries. We determine physical parameters and estimate distances based on atmospheric model analyses. Three new WDs are modeled to lie within 25 pc. Two additional WDs are confirmed to be metal-polluted (DAZ). Follow-up time series photometry confirms another object to be a pulsating ZZ Ceti WD.

Towards efficient and precise queries over ten million asteroid trajectory models

We measure the two-point cross-correlation function of C IV absorber systems and quasars, using spectroscopic data from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS; Data Release 9). The 19,701 quasars and 6149 C IV moderate absorbers, 0.28 A 0.28 A C IV absorbers at z ~ 2.3 are typically found in dark matter halos that have masses ≥1011.3-1013.4 M ☉ at that redshift. The complete BOSS sample will triple the number of both quasars and absorption systems and increase the power of this cross-correlation measurement by a factor of two.

Atmospheric PSF Interpolation for Weak Lensing in Short Exposure Imaging Data

Scientific discoveries are increasingly driven by analyzing large volumes of image data. Many new libraries and specialized database management systems (DBMSs) have emerged to support such tasks. It is unclear how well these systems support real-world image analysis use cases, and how performant the image analytics tasks implemented on top of such systems are. In this paper, we present the first comprehensive evaluation of large-scale image analysis systems using two real-world scientific image data processing use cases. We evaluate five representative systems (SciDB, Myria, Spark, Dask, and TensorFlow) and find that each of them has shortcomings that complicate implementation or hurt performance. Such shortcomings lead to new research opportunities in making large-scale image analysis both efficient and easy to use.

Atmospheric point spread function interpolation for weak lensing in short exposure imaging data

The new generation of telescopes under construction return to the same area of the sky with sufficient frequency to enable tracking of moving objects such as asteroids, near-earth objects, and comets [4,5]. To detect these moving objects, one image may be subtracted from another (separated by several days or weeks) to differentiate variable and moving sources from the dense background of stars and galaxies. Moving sources may then be identified by querying against a database of expected positions of known asteroids. At a high-level, this task maps onto executing the query: “Return all known asteroids that are expected to be located within a given region at a given time.” We consider the problem of querying for asteroids in a specified interval in space and time, specifically as applied to populating the simulations of the data flow from the Large Synoptic Survey Telescope (LSST).