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Search Results: 1 - 10 of 185372 matches for " James E. Gunn "
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The propagation of uncertainties in stellar population synthesis modeling III: model calibration, comparison, and evaluation
Charlie Conroy,James E. Gunn
Physics , 2009, DOI: 10.1088/0004-637X/712/2/833
Abstract: Stellar population synthesis (SPS) provides the link between the stellar and dust content of galaxies and their observed spectral energy distributions. In the present work we perform a comprehensive calibration of our own flexible SPS (FSPS) model against a suite of data. Several public SPS models are intercompared, including the models of Bruzual & Charlot (BC03), Maraston (M05) and FSPS. The relative strengths and weaknesses of these models are evaluated, with the following conclusions: 1) The FSPS and BC03 models compare favorably with MC data at all ages, whereas M05 colors are too red and the age-dependence is incorrect; 2) All models yield similar optical and near-IR colors for old metal-poor systems, and yet they all provide poor fits to the integrated J-K and V-K colors of both MW and M31 star clusters; 4) All models predict ugr colors too red, D4000 strengths too strong and Hdelta strengths too weak compared to massive red sequence galaxies, under the assumption that such galaxies are composed solely of old metal-rich stars; 5) FSPS and, to a lesser extent, BC03 can reproduce the optical and near-IR colors of post-starburst galaxies, while M05 cannot. Reasons for these discrepancies are explored. The failure at predicting the ugr colors, D4000, and Hdelta strengths can be explained by some combination of a minority population of metal-poor stars, young stars, blue straggler and/or blue horizontal branch stars, but not by appealing to inadequacies in either theoretical stellar atmospheres or canonical evolutionary phases (e.g., the main sequence turn-off). We emphasize that due to a lack of calibrating star cluster data in regions of the metallicity-age plane relevant for galaxies, all of these models continue to suffer from serious uncertainties that are difficult to quantify. (ABRIDGED)
Volume phase holographic gratings for the Subaru Prime Focus Spectrograph: performance measurements of the prototype grating set
Robert Barkhouser,James Arns,James E. Gunn
Physics , 2014, DOI: 10.1117/12.2057337
Abstract: The Prime Focus Spectrograph (PFS) is a major instrument under development for the 8.2 m Subaru telescope. Four identical spectrograph modules are located in a room above one Nasmyth focus. A 55~m fiber optic cable feeds light to the spectrographs from a robotic positioner at the prime focus, behind the wide-field corrector developed for Hyper Suprime-Cam. The positioner contains 2400 fibers and covers a 1.3~degree hexagonal field of view. The spectrograph optical design consists of a Schmidt collimator, two dichroic beamsplitters to split the light into three channels, and for each channel a volume phase holographic (VPH) grating and a dual-corrector, modified Schmidt reimaging camera. This design provides a 275~mm collimated beam diameter, wide simultaneous wavelength coverage from 380~nm to 1.26~\textmu m, and good imaging performance at the fast f/1.05 focal ratio required from the cameras to avoid oversampling the fibers. The three channels are designated as the blue, red, and near-infrared (NIR), and cover the bandpasses 380--650~nm (blue), 630--970~nm (red), and 0.94--1.26~\textmu m (NIR). A mosaic of two Hamamatsu 2k$\times$4k, 15~\textmu m pixel CCDs records the spectra in the blue and red channels, while the NIR channel employs a 4k$\times$4k, substrate-removed HAWAII-4RG array from Teledyne, with 15~\textmu m pixels and a 1.7~\textmu m wavelength cutoff. VPH gratings were an obvious choice for PFS and a set of three prototype VPH gratings (one each of the blue, red, and NIR designs) was ordered and has been recently delivered. In this paper we present the design and specifications for the PFS gratings, the plan and setups used for testing both the prototype and final gratings, and results from recent optical testing of the prototype grating set.
The Sloan Digital Sky Survey
James E. Gunn,David H. Weinberg
Physics , 1994,
Abstract: We summarize the plans for and the current status of the Sloan Digital Sky Survey, a digital imaging and spectroscopic survey of $\pi$ steradians in the northern Galactic cap. The CCD photometric survey will produce images in five bands to limiting magnitudes of order 23. The spectroscopic survey will obtain redshifts of $10^6$ galaxies (a complete sample to a limiting magnitude $r' \sim 18$) and $10^5$ quasars ($g' \sim 19$). Repeated imaging of a 200 deg$^2$ strip in the southern Galactic cap will yield information about variable objects and a co-added photometric catalog roughly two magnitudes deeper than the northern survey. A dedicated 2.5-meter telescope, a large multi-CCD camera, and two fiber-fed double spectrographs are under construction and should be operational by fall of 1995. The main galaxy redshift sample will have a median redshift $\langle z \rangle \approx 0.1$.
The propagation of uncertainties in stellar population synthesis modeling II: The challenge of comparing galaxy evolution models to observations
Charlie Conroy,Martin White,James E. Gunn
Physics , 2009, DOI: 10.1088/0004-637X/708/1/58
Abstract: Models for the formation and evolution of galaxies readily predict physical properties such as the star formation rates, metal enrichment histories, and, increasingly, gas and dust content of synthetic galaxies. Such predictions are frequently compared to the spectral energy distributions of observed galaxies via the stellar population synthesis (SPS) technique. Substantial uncertainties in SPS exist, and yet their relevance to the task of comparing galaxy evolution models to observations has received little attention. In the present work we begin to address this issue by investigating the importance of uncertainties in stellar evolution, the initial stellar mass function (IMF), and dust and interstellar medium (ISM) properties on the translation from models to observations. We demonstrate that these uncertainties translate into substantial uncertainties in the ultraviolet, optical, and near-infrared colors of synthetic galaxies. Aspects that carry significant uncertainties include the logarithmic slope of the IMF above 1 Msun, dust attenuation law, molecular cloud disruption timescale, clumpiness of the ISM, fraction of unobscured starlight, and treatment of advanced stages of stellar evolution including blue stragglers, the horizontal branch, and the thermally-pulsating asymptotic giant branch. The interpretation of the resulting uncertainties in the derived colors is highly non-trivial because many of the uncertainties are likely systematic, and possibly correlated with the physical properties of galaxies. We therefore urge caution when comparing models to observations.
A Catalog of Digital Images of 113 Nearby Galaxies
Zsolt Frei,Puragra Guhathakurta,James E. Gunn,J. Anthony Tyson
Physics , 1995, DOI: 10.1086/117771
Abstract: We present a digital catalog of images of 113 galaxies in this paper. These galaxies are all nearby, bright, large and well resolved. All images were recorded with charge coupled devices (CCDs) at the Palomar Observatory with the 1.5 meter telescope and at the Lowell Observatory with the 1.1 meter telescope. At Palomar we used the Thuan--Gunn g, r and i photometric bands to take 3 images each of 31 spiral galaxies; at Lowell we used the B_J and R bands (2 images per galaxy) of the photometric system by Gullixson et al. (1995) to observe 82 spirals and ellipticals. The galaxies were selected to span the Hubble classification classes. All data are photometrically calibrated with foreground stars removed. Important data on these galaxies published in the "Third Reference Catalog of Bright Galaxies" (RC3) are recorded in the FITS file headers. All files are available through anonymous FTP from ftp://astro.princeton.edu/, through WWW at http://astro.princeton.edu/~frei/galaxy_catalog.html, and Princeton University Press will soon publish the data on CD-ROM.
Confirmation of general relativity on large scales from weak lensing and galaxy velocities
Reinabelle Reyes,Rachel Mandelbaum,Uros Seljak,Tobias Baldauf,James E. Gunn,Lucas Lombriser,Robert E. Smith
Physics , 2010, DOI: 10.1038/nature08857
Abstract: Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect3. Here we report that EG = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG $\approx$ 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.
CCD Readout Electronics for the Subaru Prime Focus Spectrograph
Stephen C. Hope,James E. Gunn,Craig P. Loomis,Roger E. Fitzgerald,Grant O. Peacock
Physics , 2014, DOI: 10.1117/12.2057166
Abstract: We present details of the design for the CCD readout electronics for the Subaru Telescope Prime Focus Spectrograph (PFS). The spectrograph is comprised of four identical spectrograph modules, each collecting roughly 600 spectra. The spectrograph modules provide simultaneous wavelength coverage over the entire band from 380 nm to 1260 nm through the use of three separate optical channels: blue, red, and near infrared (NIR). A camera in each channel images the multi-object spectra onto a 4k x 4k, 15 um pixel, detector format. The two visible cameras use a pair of Hamamatsu 2k x 4k CCDs with readout provided by custom electronics, while the NIR camera uses a single Teledyne HgCdTe 4k x 4k detector and ASIC Sidecar to read the device. The CCD readout system is a custom design comprised of three electrical subsystems: the Back End Electronics (BEE), the Front End Electronics (FEE), and a Pre-amplifier. The BEE is an off-the-shelf PC104 computer, with an auxiliary Xilinx FPGA module. The computer serves as the main interface to the Subaru messaging hub and controls other peripheral devices associated with the camera, while the FPGA is used to generate the necessary clocks and transfer image data from the CCDs. The FEE board sets clock biases, substrate bias, and CDS offsets. It also monitors bias voltages, offset voltages, power rail voltage, substrate voltage and CCD temperature. The board translates LVDS clock signals to biased clocks and returns digitized analog data via LVDS. Monitoring and control messages are sent from the BEE to the FEE using a standard serial interface. The Pre-amplifier board resides behind the detectors and acts as an interface to the two Hamamatsu CCDs. The Pre-amplifier passes clocks and biases to the CCDs, and analog CCD data is buffered and amplified prior to being returned to the FEE.
Characterisation of Sloan Digital Sky Survey Stellar Photometry
Masataka Fukugita,Naoki Yasuda,Mamoru Doi,James E. Gunn,Donald G. York
Physics , 2010, DOI: 10.1088/0004-6256/141/2/47
Abstract: We study the photometric properties of stars in the data archive of the Sloan Digital Sky Survey (SDSS), the prime aim being to understand the photometric calibration over the entire data set. It is confirmed that the photometric calibration for point sources has been made overall tightly against the SDSS standard stars. We have also confirmed that photometric synthesis of the SDSS spectrophotometric data gives broad band fluxes that agree with broad band photometry with errors no more than 0.04 mag and little tilt along the wide range of colours, verifying that the response functions of the SDSS 2.5 m telescope system are well characterised. We locate stars in the SDSS photometric system, so that stars can roughly be classified into spectral classes from the colour information. We show how metallicity and surface gravity affect colours, and that stars contained in the SDSS general catalogue, plotted in colour space, show the distribution that matches well with what is anticipated from the variations of metallicity and surface gravity. The colour-colour plots are perfectly consistent among the three samples, stars in the SDSS general catalogue, SDSS standard stars and spectrophotometric stars of Gunn & Stryker, especially when some considerations are taken into account of the differences (primarily metallicity) of the samples. We show that the g-r - inverse temperature relation is tight and can be used as a good estimator of the effective temperature of stars over a fairly wide range of effective temperatures. We also confirm that the colours of G2V stars in the SDSS photometric system match well with the Sun.
A Study of Quasar Clustering at z>2.7 from the Palomar Transit Grism Survey
Andrew W. Stephens,Donald P. Schneider,Maarten Schmidt,James E. Gunn,David H. Weinberg
Physics , 1997, DOI: 10.1086/118450
Abstract: The quest for structure indicators at earlier and earlier times in the evolution of the universe has led to the search for objects with ever higher redshifts. The Palomar Transit Grism Survey has produced a large sample of high redshift quasars ($z>2.7$), allowing statistical analysis of correlation between quasar positions. In this study, clustering is identified through comparison with $100 000$ Monte Carlo generated, randomly populated volumes, which are identical to the observed region in spatial coordinates, redshift distribution, and number of quasars. Three pairs have been observed with comoving separations of 11.34, 12.97, and 24.13 h_{50}^{-1}Mpc (assuming $q_0=0.5$), smaller separations than would be expected to arise by chance in an unclustered distribution. Selection effects are ruled out as a false source of clustering by scrambling the observed quasar coordinates and redshifts, which gives a pair separation distribution nearly identical to that of the Monte Carlo distribution. Tests using the distribution of pair separations and nearest neighbor distances show that the observed pairs have a probability less than 0.1% of arising in an unclustered distribution. Using a maximum likelihood technique to estimate the correlation length $r_0$, assuming $\xi(r) = (r/r_0)^{-1.8}$, we find $r_0 = 35\pm15 h_{50}^{-1}Mpc$ (comoving, $q_0=0.5$, 1$\sigma$ errors), a value much larger than the correlation length of present-day galaxies.
A photometricity and extinction monitor at the Apache Point Observatory
David W. Hogg,Douglas P. Finkbeiner,David J. Schlegel,James E. Gunn
Physics , 2001, DOI: 10.1086/323103
Abstract: An unsupervised software ``robot'' that automatically and robustly reduces and analyzes CCD observations of photometric standard stars is described. The robot measures extinction coefficients and other photometric parameters in real time and, more carefully, on the next day. It also reduces and analyzes data from an all-sky $10 \mu m$ camera to detect clouds; photometric data taken during cloudy periods are automatically rejected. The robot reports its findings back to observers and data analysts via the World-Wide Web. It can be used to assess photometricity, and to build data on site conditions. The robot's automated and uniform site monitoring represents a minimum standard for any observing site with queue scheduling, a public data archive, or likely participation in any future National Virtual Observatory.
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