Mark U. SubbaRao

The multi-object, fiber-fed spectrographs for the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyα absorption of 160,000 high redshift quasars over 10,000 deg2 of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = λ/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < λ < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.

The evolution of the global star formation history as measured from the Hubble Deep Field

The Hubble Deep Field (HDF) is the deepest set of multicolor optical photometric observations ever undertaken, and it offers a valuable data set with which to study galaxy evolution. Combining the optical WFPC2 data with ground-based near-infrared photometry, we derive photometrically estimated redshifts for HDF galaxies with J 2, and they bridge the redshift gap between those two samples. The overall star formation or metal enrichment rate history is consistent with the theoretical models of White and Frenk and the predictions of Pei and Fall based on the evolving H I content of Lyα QSO absorption line systems.

The sloan digital sky survey quasar catalog. IV. Fifth data release

We present the fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog contains 77,429 objects; this is an increase of over 30,000 entries since the previous edition. The catalog consists of the objects in the SDSS Fifth Data Release that have luminosities larger than Mi = -22.0 (in a cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), have at least one emission line with FWHM larger than 1000 km s-1 or have interesting/complex absorption features, are fainter than i ≈ 15.0, and have highly reliable redshifts. The area covered by the catalog is ≈5740 deg2. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the catalog includes 891 quasars at redshifts greater than 4, of which 36 are at redshifts greater than 5. Approximately half of the catalog quasars have i < 19; nearly all have i < 21. For each object the catalog presents positions accurate to better than 0.2 rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains basic radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 A at a spectral resolution of 2000; the spectra can be retrieved from the public database using the information provided in the catalog. The average SDSS colors of quasars as a function of redshift, derived from the catalog entries, are presented in tabular form. Approximately 96% of the objects in the catalog were discovered by the SDSS.

Early-type galaxies in the SDSS. III. The Fundamental Plane

A magnitude-limited sample of nearly 9000 early-type galaxies in the redshift range 0.01 ≤ z ≤ 0.3 was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. The fundamental plane relation in this sample is Ro ∝ σ1.49±0.05I in the r* band. It is approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only a little. If the fundamental plane is used to quantify this evolution, then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population that formed the bulk of its stars about 9 Gyr ago. One of the principal advantages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The fundamental plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.

The Sloan Digital Sky Survey Quasar Catalog III. Third Data Release

We present the third edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than Mi = -22 (in a cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), have at least one emission line with FWHM larger than 1000xa0kmxa0s-1 or are unambiguously broad absorption line quasars, are fainter than i = 15.0, and have highly reliable redshifts. The area covered by the catalog is ≈4188xa0deg2. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than 4, of which 17 are at redshifts greater than 5. For each object the catalog presents positions accurate to better than 02 rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03xa0mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800–9200 A at a spectral resolution of 2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.

The sloan digital sky survey quasar catalog. II. First data release

We present the second edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 16,713 objects in the SDSS First Data Release that have luminosities larger than Mi = -22 (in a cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), have at least one emission line with FWHM larger than 1000 km s-1, and have highly reliable redshifts. The area covered by the catalog is ≈1360 deg2. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.43. For each object, the catalog presents positions accurate to better than 02 rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains some radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. Calibrated digital spectra of all objects in the catalog, covering the wavelength region 3800–9200 A at a spectral resolution of 1800–2100, are available. This publication supersedes the first SDSS Quasar Catalog, which was based on material from the SDSS Early Data Release. A summary of corrections to current quasar databases is also provided. The majority of the objects were found in SDSS commissioning data using a multicolor selection technique. Since the quasar selection algorithm was undergoing testing during the entire observational period covered by this catalog, care must be taken when assembling samples from the catalog for use in statistical studies. A total of 15,786 objects (94%) in the catalog were discovered by the SDSS; 12,173 of the SDSS discoveries are reported here for the first time. Included in the new discoveries are five quasars brighter than i = 16.0 and 17 quasars with redshifts larger than 4.5.

A Blind Test of Photometric Redshift Prediction

Results of a blind test of photometric redshift predictions against spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck Telescope are presented. The best photometric redshift schemes predict spectroscopic redshifts with a redshift accuracy of Δz < 0.1 for more than 68% of sources and with Δz < 0.3 for 100%, when single-feature spectroscopic redshifts are removed from consideration. This test shows that photometric redshift schemes work well, at least when the photometric data are of high quality and when the sources are at moderate redshifts.

The Near-Infrared Number Counts and Luminosity Functions of Local Galaxies

This study presents a wide-field near-infrared (K-band) survey in two fields: SA 68 and Lynx 2. The survey covers an area of 0.6 deg2, complete to K = 16.5. A total of 867 galaxies are detected in this survey of which 175 have available redshifts. The near-infrared number counts to K = 16.5 mag are estimated from the complete photometric survey and are found to be in close agreement with other available studies. The sample is corrected for incompleteness in redshift space, using selection function in the form of a Fermi-Dirac distribution. This is then used to estimate the local near-infrared luminosity function (IRLF) of galaxies. A Schechter fit to the infrared data gives M*K=-25.1±0.3, α = -1.3 ± 0.2, and * = (1.5 ± 0.5) × 10-3 Mpc-3 (for H0 = 50 km s-1 Mpc-1 and q0 = 0.5). When reduced to α = -1, this agrees with other available estimates of the local IRLF. We find a steeper slope for the faint end of the infrared luminosity function when compared to previous studies. This is interpreted as being due to the presence of a population of faint but evolved (metal-rich) galaxies in the local universe. However, it is not from the same population as the faint blue galaxies found in the optical surveys. The characteristic magnitude (M*K) of the local IRLF indicates that the bright red galaxies (MK ~ -27 mag) have a space density of ≤5 × 10-5 Mpc-3 and, hence, are not likely to be local objects.

Planetary-Scale Terrain Composition

Many interrelated planetary height map and surface image map data sets exist, and more data are collected each day. Broad communities of scientists require tools to compose these data interactively and explore them via real-time visualization. While related, these data sets are often unregistered with one another, having different projection, resolution, format, and type. We present a GPU-centric approach to the real-time composition and display of unregistered-but-related planetary-scale data. This approach employs a GPGPU process to tessellate spherical height fields. It uses a render-to-vertex-buffer technique to operate upon polygonal surface meshes in image space, allowing geometry processes to be expressed in terms of image processing. With height and surface map data processing unified in this fashion, a number of powerful composition operations may be uniformly applied to both. Examples include adaptation to nonuniform sampling due to projection, seamless blending of data of disparate resolution or transformation regardless of boundary, and the smooth interpolation of levels of detail in both geometry and imagery. Issues of scalability and precision are addressed, giving out-of-core access to giga-pixel data sources, and correct rendering at scales approaching one meter.

Luminosity Functions From Photometric Redshifts. I. Techniques

The determination of the galaxy luminosity function is an active and fundamental field in observational cosmology. In this paper we propose a cost effective way of measuring galaxy luminosity functions at faint magnitudes. Our technique employs the use of galaxy redshifts estimated from their multicolor photometry (Connolly et al. 1995). Associated with the redshift estimate is a well defined error distribution. We have derived a variant of Lynden-Bells (1971) C--method that considers, for each galaxy, the probability distribution in absolute magnitude resultant from the redshift error. This technique is tested through simulations and potential biases are quantified. We then apply the technique to a sample of galaxies with multicolor photometric data at moderately faint (B=23) limits, and compare the results to a subset of these data with spectroscopic redshifts. We find that the luminosity function derived from the photometric redshifts is consistent with that determined from spectroscopic redshifts.