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Jeffrey A. Munn

Publications and source records attributed to Jeffrey A. Munn.

43 records · Page 3Linked to original sources

Astrometric Calibration of the Sloan Digital Sky Survey

The astrometric calibration of the Sloan Digital Sky Survey is described. For point sources brighter than r ~ 20 the astrometric accuracy is 45 milliarcseconds (mas) rms per coordinate when reduced against the USNO CCD Astrograph Catalog, and 75 mas rms when reduced against Tycho-2, with an additional 20 - 30 mas systematic error in both cases. The rms errors are dominated by anomalous refraction and random errors in the primary reference catalogs. The relative astrometric accuracy between the r filter and each of the other filters (u g i z) is 25 - 35 mas rms. At the survey limit (r ~ 22), the astrometric accuracy is limited by photon statistics to approximately 100 mas rms for typical seeing. Anomalous refraction is shown to contain components correlated over two or more degrees on the sky.

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The Galaxy Luminosity Function and Luminosity Density at Redshift z=0.1

Using a catalog of 147,986 galaxy redshifts and fluxes from the Sloan Digital Sky Survey (SDSS) we measure the galaxy luminosity density at z=0.1 in five optical bandpasses corresponding to the SDSS bandpasses shifted to match their restframe shape at z=0.1. We denote the bands {0.1}{u}, {0.1}{g}, {0.1}{r}, {0.1}{i}, {0.1}{z}, with λ_{eff} = [3216, 4240, 5595, 6792, 8111] Angstroms respectively. We use a maximum likelihood method which allows for a general form for the shape of the luminosity function, simple luminosity and number evolution, incorporates flux uncertainties, and accounts for the flux limits of the survey. We find luminosity densities at z=0.1 in absolute AB magnitudes in a Mpc^3 of [-14.10 \pm 0.15, -15.18 \pm 0.03, -15.90 \pm 0.03, -16.24 \pm 0.03, -16.56 \pm 0.02] in [{0.1}{u}, {0.1}{g}, {0.1}{r}, {0.1}{i}, {0.1}{z}], respectively, using Ω_0 =0.3, Ω_Λ=0.7, and h=1, and using Petrosian magnitudes. Similar results are obtained using Sersic model magnitudes, suggesting that flux from outside the Petrosian apertures is not a major correction. In the {0.1}{r} band, the best fit Schechter function to our results has ϕ_\ast = (1.49 \pm 0.04) \times 10^{-2} h^3 Mpc^{-3}, M_\ast - 5\log_{10} h = -20.44 \pm 0.01, and α= -1.05\pm 0.01. In solar luminosities, the luminosity density in {0.1}{r} is (1.84 \pm 0.04) h 10^8 L_{{0.1}{r},\odot} Mpc^{-3}. Our results are consistent with other estimates of the luminosity density, from the Two-degree Field Galaxy Redshift Survey and the Millenium Galaxy Catalog. They represent a substantial change (\sim 0.5 mag) from earlier SDSS luminosity density results based on commissioning data, almost entirely because of the inclusion of evolution in the luminosity function model.

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Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar

We present moderate resolution Keck spectroscopy of quasars at z=5.82, 5.99 and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Ly Alpha absorption in the spectra of these quasars evolves strongly with redshift. To z~5.7, the Ly Alpha absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest redshift object, SDSSp J103027.10+052455.0 (z=6.28), the average transmitted flux is 0.0038+-0.0026 times that of the continuum level over 8450 A < lambda < 8710 A (5.95 150, and is consistent with zero flux in the Ly Alpha forest region immediately blueward of the Ly Alpha emission line, compared with a drop by a factor of ~10 at z(abs)~5.3. A similar break is seen at Ly Beta; because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, tau(eff) > 20, on the optical depth to Ly Alpha absorption at z=6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Ly Alpha forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z~5 to 6, and the universe is approaching the reionization epoch at z~6.

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Galaxy Mass and Luminosity Scaling Laws Determined by Weak Gravitational Lensing

We present new measurements of scaling laws relating the luminosity of galaxies to the amplitude and shape of their dark matter halos. Early imaging and spectroscopic data from the Sloan Digital Sky Survey are used to make weak lensing measurements of the surface mass density contrast Delta Sigma_+ around classes of lens objects. This surface mass density contrast as a function of radius is a measure of the galaxy-mass correlation function (GMCF). Because spectroscopic redshifts are available for all lens objects, the mass and distance scales are well constrained. The GMCF measured around ~31,000 lenses is well fit by a power law of the form Delta Sigma_+ = (2.5+0.7-0.6) (R/1 Mpc)^{-0.8+-0.2} h M_sun pc^-2. We compare this GMCF to galaxy luminosity, type, and environment, and find that it varies strongly with all three. We quantify these variations by comparing the normalization of a fit to the inner 260 h^-1 kpc, M_260, to the galaxy luminosity. While M_260 is not strongly related to luminosity in bluest band u', there is a simple, linear relation between M_260 and luminosity in redder bands (g', r', i', and z'). We test the universality of these mass-to-light scalings by independently measuring them for spiral and elliptical galaxies,and for galaxies in a variety of environments. We find remarkable consistency in these determinations in the red bands, especially i' and z'. This consistency across a wide range of systems suggests that the measured scaling represents an excellent cosmic average, and that the integrated star formation history of galaxies is strongly related to the dark matter environments in which they form.

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Weak Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky Survey (SDSS) commissioning data. Cluster candidates are selected optically from SDSS imaging data and confirmed for this study by matching to X-ray sources found independently in the ROSAT all sky survey (RASS). Five color SDSS photometry is used to make accurate photometric redshift estimates that are used to rescale and combine the lensing measurements. The mean shear from these clusters is detected to 2 h-1 Mpc at the 7-sigma level, corresponding to a mass within that radius of 4.2 +/- 0.6 x 10^14 h-1 M_sun. The shear profile is well fit by a power law with index -0.9 +/- 0.3, consistent with that of an isothermal density profile. This paper demonstrates our ability to measure ensemble cluster masses from SDSS imaging data.

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Spectroscopy of Quasar Candidates from SDSS Commissioning Data

The Sloan Digital Sky Survey has obtained images in five broad-band colors for several hundred square degrees. We present color-color diagrams for stellar objects, and demonstrate that quasars are easily distinguished from stars by their distinctive colors. Follow-up spectroscopy in less than ten nights of telescope time has yielded 22 new quasars, 9 of them at $z> 3.65$, and one with $z = 4.75$, the second highest-redshift quasar yet known. Roughly 80% of the high-redshift quasar candidates selected by color indeed turn out to be high-redshift quasars.

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The Luminosity Function for L>L* Galaxies at z > 3

Through use of multiband (U, B, R, I) photometry we have isolated high redshift (3.0 L* luminosity function for z = 3-5 galaxies obtained by a photometric redshift analysis of the Hubble Deep Field (HDF) by Gwyn & Hartwick (1996). Our results at R ~ 23 are more consistent with the photometric redshift analysis of the faint HDF galaxies by Sawicki & Yee (1996), but our present upper limits at the brightest magnitudes (R < 21.5, M(R) < -24) allow more generous volume densities of these super-L* galaxies.

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