Browsing by Subject "surveys"

Now showing 1 - 12 of 12
  • Thumbnail Image
    Item
    Open Access
    A catalogue of galaxies behind the southern Milky Way: II. The Crux and Great Attractor regions ($lapprox$ 289° to 338°)
    (2001) Woudt, P A; Kraan-Korteweg, R C
    In this second paper of the catalogue series of galaxies behind the southern Milky Way, we report on the deep optical galaxy search in the Crux region (
  • Thumbnail Image
    Item
    Open Access
    A new approach to the optimal target selection problem
    (2007) Elson, E C; Bassett, B A; van der Heyden, K; Vilakazi, Z Z
    Context.This paper addresses a common problem in astronomy and cosmology: to optimally select a subset of targets from a larger catalog. A specific example is the selection of targets from an imaging survey for multi-object spectrographic follow-up.Aims.We present a new heuristic optimisation algorithm, HYBRID, for this purpose and undertake detailed studies of its performance.Methods.HYBRID combines elements of the simulated annealing, MCMC and particle-swarm methods and is particularly successful in cases where the survey landscape has multiple curvature or clustering scales.Results.HYBRID consistently outperforms the other methods, especially in high-dimensionality spaces with many extrema. This means many fewer simulations must be run to reach a given performance confidence level and implies very significant advantages in solving complex or computationally expensive optimisation problems.Conclusions.HYBRID outperforms both MCMC and SA in all cases including optimisation of high dimensional continuous surfaces indicating that HYBRID is useful far beyond the specific problem of optimal target selection. Future work will apply HYBRID to target selection for the new 10 m Southern African Large Telescope in South Africa.
  • Thumbnail Image
    Item
    Open Access
    Deep Ks -near-infrared surface photometry of 80 dwarf irregular galaxies in the local volume
    (2010) Fingerhut, Robin L; McCall, Marshall L; Argote, Mauricio; Cluver, Michelle E; Nishiyama, Shogo; Rekola, Rami T F; Richer, Michael G; Vaduvescu, Ovidiu; Woudt, Patrick A
    We present deep near-infrared (K_s) images and surface photometry for 80 dwarf irregular galaxies (dIs) within ~5 Mpc of the Milky Way. The galaxy images were obtained at five different facilities between 2004 and 2006. The image reductions and surface photometry have been performed using methods specifically designed for isolating faint galaxies from the high and varying near-infrared sky level. Fifty-four of the 80 dIs have surface brightness profiles which could be fit to a hyperbolic-secant (sech) function, while the remaining profiles could be fit to the sum of a sech and a Gaussian function. From these fits, we have measured central surface brightnesses, scale lengths, and integrated magnitudes. This survey is part of a larger study of the connection between large-scale structure and the global properties of dIs, the hypothesized building-blocks of more massive galaxies.
  • Thumbnail Image
    Item
    Restricted
    Demographic profile and perceived INSET needs of secondary Mathematics teachers in Limpopo province
    (2010) Laugksch, Rudiger
    The findings of a study on the demographic profile and perceived INSET needs of secondary Mathematics teachers in Limpopo province are described. The survey instrument employed was the Science Teacher Inventory of Needs for Limpopo province (STIN-LP). Most teachers who responded to this survey teach at a rural or township school, are between 20 and 40 years old, and have between four and ten years experience in teaching Mathematics. Standard 10 is the highest academic qualification of half of the teachers, with 67% of teachers having an M+3 as their highest professional qualification. Teachers indicated interest in all the 38 INSET need items included in the STIN-LP with motivating learners to learn Mathematics, using audio-visual equipment and applying mathematics to daily life of learners among the most important need. The least support was indicated, among others, for needs related to the history of mathematics, improving content knowledge, how mathematics is used in society, and teaching large classes. Poor communication of INSET activities was reported to be the greatest barrier to INSET participation. Implications of the findings are discussed.
  • Thumbnail Image
    Item
    Open Access
    Extragalactic large-scale structures behind the southern Milky Way: IV. Redshifts obtained with MEFOS
    (2004) Woudt, P A; Kraan-Korteweg, R C; Cayatte, V; Balkowski, C; Felenbok, P
    Abbreviated: As part of our efforts to unveil extragalactic large-scale structures behind the southern Milky Way, we here present redshifts for 764 galaxies in the Hydra/Antlia, Crux and Great Attractor region (266deg < l < 338deg, < 10deg), obtained with the Meudon-ESO Fibre Object Spectrograph (MEFOS) at the 3.6-m telescope of ESO. The observations are part of a redshift survey of partially obscured galaxies recorded in the course of a deep optical galaxy search behind the southern Milky Way. A total of 947 galaxies have been observed, a small percentage of the spectra (N=109, 11.5%) were contaminated by foreground stars, and 74 galaxies (7.8%) were too faint to allow a reliable redshift determination. With MEFOS we obtained spectra down to the faintest galaxies of our optical galaxy survey, and hence probe large-scale structures out to larger distances (v <~ 30000 km/s) than our other redshift follow-ups. The most distinct large-scale structures revealed in the southern Zone of Avoidance are discussed in context to known structures adjacent to the Milky Way.
  • Thumbnail Image
    Item
    Open Access
    NTT and NOT spectroscopy of SDSS-II supernovae
    (2011) Östman, L; Nordin, J; Goobar, A; Amanullah, R; Smith, M; Sollerman, J; Stanishev, V; Stritzinger, M D; Bassett, B A; Davis, T M; Edmondson, E; Frieman, J A; Garnavich, P M; Lampeitl, H; Leloudas, G; Marriner, J; Nichol, R C; Romer, K; Sako, M; Schneider, D P; Zheng, C
    Context. The Sloan Digital Sky Survey II (SDSS-II) Supernova Survey, conducted between 2005 and 2007, was designed to detect a large number of type Ia supernovae around z ∼ 0.2, the redshift “gap” between low-z and high-z supernova searches. The survey has provided multi-band (ugriz) photometric lightcurves for variable targets, and supernova candidates were scheduled for spectroscopic observations, primarily to provide supernova classification and accurate redshifts. We present supernova spectra obtained in 2006 and 2007 using the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT). Aims. We provide an atlas of supernova spectra in the range z = 0.03−0.32 that complements the well-sampled lightcurves from SDSS-II in the forthcoming three-year SDSS supernova cosmology analysis. The sample can, for example, be used for spectral studies of type Ia supernovae, which are critical for understanding potential systematic effects when supernovae are used to determine cosmological distances. Methods. The spectra were reduced in a uniform manner, and special care was taken in estimating the uncertainties for the different processing steps. Host-galaxy light was subtracted when possible and the supernova type fitted using the SuperNova IDentification code (SNID). We also present comparisons between spectral and photometric dating using SALT lightcurve fits to the photometry from SDSS-II, as well as the global distribution of our sample in terms of the lightcurve parameters: stretch and colour. Results. We report new spectroscopic data from 141 type Ia supernovae, mainly between −9 and +15 days from lightcurve maximum, including a few cases of multi-epoch observations. This homogeneous, host-galaxy subtracted, type Ia supernova spectroscopic sample is among the largest such data sets and unique in its redshift interval. The sample includes two potential SN 1991T-like supernovae (SN 2006on and SN 2007ni) and one potential SN 2002cx-like supernova (SN 2007ie). In addition, the new compilation includes spectra from 23 confirmed type II and 8 type Ib/c supernovae.
  • Thumbnail Image
    Item
    Open Access
    Parkes H I observations of galaxies behind the southern Milky Way II. The Crux and Great Attractor regions (l ≈ 289◦ to 338◦)***
    (2009) Schröder, A C; Kraan-Korteweg, R C; Henning, P A
    As part of our programme to map the large-scale distribution of galaxies behind the southern Milky Way, we observed 314 optically-selected, partially-obscured galaxies in the Zone of Avoidance (ZOA) in the Crux and Great Attractor (GA) regions. An additional 29 galaxies were observed in the Vela ZOA survey region (because of the small numbers they are not discussed any further). The observations were conducted with the Parkes 64 m (210 ft) radio telescope, in a single-pixel pointed mode, reaching an rms noise level of typically $2{-}6$ mJy over the velocity search range of 400 < v < 10 500 km s-1. A total of 162 galaxies were detected (plus 14 galaxies in the Vela region). The detection rate is slightly higher than for the Hydra/Antlia region (52% versus 45%) observed in the same way. This can be explained by the prominence of the GA overdensity in the survey regions, which leads to a relatively higher fraction of nearby galaxies. It is also evident from the quite narrow velocity distribution (largely confined to $3000{-}6000$ km s-1) and deviates significantly from the expectation of a uniform galaxy distribution for the given sensitivity and velocity range. No systematic differences were found between detections and non-detections, in terms of latitude, foreground extinction, or environment, except for the very central part of the rich Norma cluster, where hardly any galaxies were detected. A detailed investigation of the H i content of the galaxies reveals strong H i deficiency at the core of the Norma cluster (within about a 0.4 Abell radius), similar to what has been found in the Coma cluster. The redshifts obtained by this observing technique result in a substantial reduction of the so-called redshift ZOA. This is obvious when analysing the large-scale structure of the new H i data in combination with data from other (optical) ZOA redshift surveys. The lower latitude detections provide further evidence of the extension of the Norma Wall, across the ZOA, in particular its bending towards the Cen-Crux clusters above the Galactic plane at slightly higher redshift, rather than a straight continuation towards the Centaurus clusters.
  • Thumbnail Image
    Item
    Open Access
    The GMRT 150 MHz all-sky radio survey: First alternative data release TGSS ADR1
    (2017) Intema, H T; Jagannathan, P; Mooley, K P; Frail, D A
    We present the first full release of a survey of the 150 MHz radio sky, observed with the Giant Metrewave Radio Telescope (GMRT) between April 2010 and March 2012 as part of the TIFR GMRT Sky Survey (TGSS) project. Aimed at producing a reliable compact source survey, our automated data reduction pipeline efficiently processed more than 2000 h of observations with minimal human interaction. Through application of innovative techniques such as image-based flagging, direction-dependent calibration of ionospheric phase errors, correcting for systematic offsets in antenna pointing, and improving the primary beam model, we created good quality images for over 95 percent of the 5336 pointings. Our data release covers 36 900 deg2 (or 3.6 π steradians) of the sky between −53° and +90° declination (Dec), which is 90 percent of the total sky. The majority of pointing images have a noise level below 5 mJy beam-1 with an approximate resolution of 25′′×25′′ (or 25′′×25′′/ cos(Dec−19°) for pointings south of 19° declination). We have produced a catalog of 0.62 Million radio sources derived from an initial, high reliability source extraction at the seven sigma level. For the bulk of the survey, the measured overall astrometric accuracy is better than two arcseconds in right ascension and declination, while the flux density accuracy is estimated at approximately ten percent. Within the scope of the TGSS alternative data release (TGSS ADR) project, the source catalog, as well as 5336 mosaic images (5°×5°) and an image cutout service, are made publicly available at the CDS as a service to the astronomical community. Next to enabling a wide range of different scientific investigations, we anticipate that these survey products will provide a solid reference for various new low-frequency radio aperture array telescopes (LOFAR, LWA, MWA, SKA-low), and can play an important role in characterizing the epoch-of-reionisation (EoR) foreground. The TGSS ADR project aims at continuously improving the quality of the survey data products. Near-future improvements include replacement of bright source snapshot images with archival targeted observations, using new observations to fill the holes in sky coverage and replace very poor quality observational data, and an improved flux calibration strategy for less severely affected observational data.
  • Thumbnail Image
    Item
    Open Access
    The LOFAR Two-metre Sky Survey: I. Survey description and preliminary data release⋆
    (2017) Shimwell, T W; Röttgering, H J A; Best, P N; Williams, W L; Dijkema, T J; de Gasperin, F; Hardcastle, M J; Heald, G H; Hoang, D N; Horneffer, A; Intema, H; Mahony, E K; Mandal, S; Mechev, A P; Morabito, L; Oonk, J B R; Rafferty, D; Retana-Montenegro, E; Sabater, J; Tasse, C; van Weeren, R J; BrYggen, M; Brunetti, G; Chyży, K T; Conway, J E; Haverkorn, M; Jackson, N; Jarvis, M J; McKean, J P; Miley, G K; Morganti, R; White, G J
    598
  • Thumbnail Image
    Item
    Open Access
    The Nainital-Cape Survey: IV. A search for pulsational variability in 108 chemically peculiar stars⋆
    (2016) Joshi, S; Martinez, P; Chowdhury, S; Chakradhari, N K; Joshi, Y C; van Heerden, P; Medupe, T; Kumar, Y B; Kuhn, R B
    Context. The Nainital-Cape Survey is a dedicated ongoing survey program to search for and study pulsational variability in chemically peculiar (CP) stars to understand their internal structure and evolution.
  • Thumbnail Image
    Item
    Open Access
    The sixth data release of the Sloan digital sky survey
    (2008) Adelman‐McCarthy, Jennifer K; AgYeros, Marcel A; Allam, Sahar S; Allende Prieto, Carlos; Anderson, Kurt S J; Anderson, Scott F; Annis, James; Bahcall, Neta A; Bailer‐Jones, C A L; Baldry, Ivan K; Barentine, J C; Bassett, Bruce A; Becker, Andrew C; Beers, Timothy C; Bell, Eric F; Berlind, Andreas A; Bernardi, Mariangela; Blanton, Michael R; Bochanski, John J; Boroski, William N; Brinchmann, Jarle; Brinkmann, J; Brunner, Robert J; Budavári, Tamás; Carliles, Samuel; Carr, Michael A; Castander, Francisco J; Cinabro, David; Cool, R J; Covey, Kevin R; Csabai, István; Cunha, Carlos E
    This paper describes the Sixth Data Release of the Sloan Digital Sky Survey. With this data release, the imaging of the northern Galactic cap is now complete. The survey contains images and parameters of roughly 287 million objects over 9583 deg2 , including scans over a large range of Galactic latitudes and longitudes. The survey also includes 1.27 million spectra of stars, galaxies, quasars, and blank sky (for sky subtraction) selected over 7425 deg2 . This release includes much more stellar spectroscopy than was available in previous data releases and also includes detailed estimates of stellar temperatures, gravities, and metallicities. The results of improved photometric calibration are now available, with uncertainties of roughly 1% in g, r, i, and z, and 2% in u, substantially better than the uncertainties in previous data releases. The spectra in this data release have improved wavelength and flux calibration, especially in the extreme blue and extreme red, leading to the qualitatively better determination of stellar types and radial velocities. The spectrophotometric fluxes are now tied to point-spread function magnitudes of stars rather than fiber magnitudes. This gives more robust results in the presence of seeing variations, but also implies a change in the spectrophotometric scale, which is now brighter by roughly 0.35 mag. Systematic errors in the velocity dispersions of galaxies have been fixed, and the results of two independent codes for determining spectral classifications and redshifts are made available. Additional spectral outputs are made available, including calibrated spectra from individual 15 minute exposures and the sky spectrum subtracted from each exposure. We also quantify a recently recognized underestimation of the brightnesses of galaxies of large angular extent due to poor sky subtraction; the bias can exceed 0.2 mag for galaxies brighter than r ¼ 14 mag.
  • Thumbnail Image
    Item
    Open Access
    Towards automatic classification of all WISE sources
    (2016) Kurcz, A; Bilicki, M; Solarz, A; Krupa, M; Pollo, A; Małek, K
    592