11 research outputs found
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 deg^2 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 First Hour of Extra-galactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster
On 26 May 1999, one of the Sloan Digital Sky Survey (SDSS) fiber-fed
spectrographs saw astronomical first light. This was followed by the first
spectroscopic commissioning run during the dark period of June 1999. We present
here the first hour of extra-galactic spectroscopy taken during these early
commissioning stages: an observation of the Coma cluster of galaxies. Our data
samples the Southern part of this cluster, out to a radius of 1.5degrees and
thus fully covers the NGC 4839 group. We outline in this paper the main
characteristics of the SDSS spectroscopic systems and provide redshifts and
spectral classifications for 196 Coma galaxies, of which 45 redshifts are new.
For the 151 galaxies in common with the literature, we find excellent agreement
between our redshift determinations and the published values. As part of our
analysis, we have investigated four different spectral classification
algorithms: spectral line strengths, a principal component decomposition, a
wavelet analysis and the fitting of spectral synthesis models to the data. We
find that a significant fraction (25%) of our observed Coma galaxies show signs
of recent star-formation activity and that the velocity dispersion of these
active galaxies (emission-line and post-starburst galaxies) is 30% larger than
the absorption-line galaxies. We also find no active galaxies within the
central (projected) 200 h-1 Kpc of the cluster. The spatial distribution of our
Coma active galaxies is consistent with that found at higher redshift for the
CNOC1 cluster survey. Beyond the core region, the fraction of bright active
galaxies appears to rise slowly out to the virial radius and are randomly
distributed within the cluster with no apparent correlation with the potential
merger of the NGC 4839 group. [ABRIDGED]Comment: Accepted in AJ, 65 pages, 20 figures, 5 table
The Multi-Object, Fiber-Fed Spectrographs for SDSS 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 Lyman-alpha
absorption of 160,000 high redshift quasars over 10,000 square degrees 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 = \lambda/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 < \lambda < 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.Comment: 43 pages, 42 figures, revised according to referee report and
accepted by AJ. Provides background for the instrument responsible for SDSS
and BOSS spectra. 4th in a series of survey technical papers released in
Summer 2012, including arXiv:1207.7137 (DR9), arXiv:1207.7326 (Spectral
Classification), and arXiv:1208.0022 (BOSS Overview
Galaxy Clustering in Early SDSS Redshift Data
We present the first measurements of clustering in the Sloan Digital Sky
Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies
with redshifts 5,700 km/s < cz < 39,000 km/s, distributed in several long but
narrow (2.5-5 degree) segments, covering 690 square degrees. For the full,
flux-limited sample, the redshift-space correlation length is approximately 8
Mpc/h. The two-dimensional correlation function \xi(r_p,\pi) shows clear
signatures of both the small-scale, ``fingers-of-God'' distortion caused by
velocity dispersions in collapsed objects and the large-scale compression
caused by coherent flows, though the latter cannot be measured with high
precision in the present sample. The inferred real-space correlation function
is well described by a power law, \xi(r)=(r/6.1+/-0.2 Mpc/h)^{-1.75+/-0.03},
for 0.1 Mpc/h < r < 16 Mpc/h. The galaxy pairwise velocity dispersion is
\sigma_{12} ~ 600+/-100 km/s for projected separations 0.15 Mpc/h < r_p < 5
Mpc/h. When we divide the sample by color, the red galaxies exhibit a stronger
and steeper real-space correlation function and a higher pairwise velocity
dispersion than do the blue galaxies. The relative behavior of subsamples
defined by high/low profile concentration or high/low surface brightness is
qualitatively similar to that of the red/blue subsamples. Our most striking
result is a clear measurement of scale-independent luminosity bias at r < 10
Mpc/h: subsamples with absolute magnitude ranges centered on M_*-1.5, M_*, and
M_*+1.5 have real-space correlation functions that are parallel power laws of
slope ~ -1.8 with correlation lengths of approximately 7.4 Mpc/h, 6.3 Mpc/h,
and 4.7 Mpc/h, respectively.Comment: 51 pages, 18 figures. Replaced to match accepted ApJ versio
Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System
We present an empirical investigation of the colors of quasars in the Sloan
Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625
quasars with SDSS photometry. The quasars are distributed in a 2.5 degree wide
stripe centered on the Celestial Equator covering square degrees.
Positions and SDSS magnitudes are given for the 898 quasars known prior to SDSS
spectroscopic commissioning. New SDSS quasars represent an increase of over
200% in the number of known quasars in this area of the sky. The ensemble
average of the observed colors of quasars in the SDSS passbands are well
represented by a power-law continuum with (). However, the contributions of the bump
and other strong emission lines have a significant effect upon the colors. The
color-redshift relation exhibits considerable structure, which may be of use in
determining photometric redshifts for quasars. The range of colors can be
accounted for by a range in the optical spectral index with a distribution
(95% confidence), but there is a red tail in the
distribution. This tail may be a sign of internal reddening. Finally, we show
that there is a continuum of properties between quasars and Seyfert galaxies
and we test the validity of the traditional division between the two classes of
AGN.Comment: 66 pages, 15 figures (3 color), accepted by A
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THE MULTI-OBJECT, FIBER-FED SPECTROGRAPHS FOR THE SLOAN DIGITAL SKY SURVEY AND THE BARYON OSCILLATION SPECTROSCOPIC SURVEY
Improved Retrievals of Carbon Dioxide from the Orbiting Carbon Observatory-2 with the version 8 ACOS algorithm [Discussion paper]
Since September 2014, NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite has been taking measurements of reflected solar spectra and using them to infer atmospheric carbon dioxide levels. This work provides details of the OCO-2 retrieval algorithm, versions 7 and 8, used to derive the column-averaged dry air mole fraction of atmospheric CO2 (XCO2) for the roughly 100,000 cloud-free measurements recorded by OCO-2 each day. The algorithm is based on the Atmospheric Carbon Observations from Space (ACOS) algorithm which has been applied to observations from the Greenhouse Gases Observing SATellite (GOSAT) since 2009, with modifications necessary for OCO-2. Because high accuracy, better than 0.25%, is required in order to accurately infer carbon sources and sinks from XCO2, significant errors and regional-scale biases in the measurements must be minimized. We discuss efforts to filter out poor quality measurements, and correct the remaining good quality measurements to minimize regional-scale biases. Updates to the radiance calibration and retrieval forward model in version 8 have improved many aspects of the retrieved data products. The version 8 data appear to have reduced regionalscale biases overall, and demonstrate a clear improvement over the version 7 data. In particular, error variance with respect to TCCON was reduced by 20% over land and 40% over ocean between versions 7 and 8, and nadir and glint observations over land are now more consistent. While this paper documents the significant improvements in the ACOS algorithm, it will continue to evolve and improve as the CO2 data record continues to expand.Part of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) for the Orbiting Carbon Observatory-2 Project. Work at Colorado State University and the Geology and Planetary Sciences Department at the California Institute of Technology was supported by subcontracts
from the OCO-2 Project
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Colors of 2625 Quasars at 0 < z < 5 Measured in the Sloan Digital Sky Survey Photometric System
We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry: 1759 quasars found during SDSS spectroscopic commissioning and SDSS follow-up observations on other telescopes, 50 matches to FIRST quasars, 573 matches to quasars from the NASA Extragalactic Database, and 243 quasars from two or more of these sources. The quasars are distributed in a 2fdg5 wide stripe centered on the celestial equator covering ~529 deg2. Positions (accurate to 0farcs2) and SDSS magnitudes are given for the 898 quasars known prior to SDSS spectroscopic commissioning. New SDSS quasars, which range in brightness from i* = 15.39 to the photometric magnitude limit of the survey, represent an increase of over 200% in the number of known quasars in this area of the sky. The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with αν = -0.5 (fν ∝ να) and are close to those predicted by previous simulations. However, the contributions of the "small blue (or λ3000) bump" and other strong emission lines have a significant effect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars from their colors alone. The range of colors at a given redshift can generally be accounted for by a range in the optical spectral index with a distribution αν = -0.5 ± 0.65 (95% confidence), but there is a red tail in the distribution. This tail may be a sign of internal reddening, especially since fainter objects at a given redshift tend to exhibit redder colors than the average. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies, and we test the validity of the traditional dividing line (MB = -23) between the two classes of active galactic nuclei.Astronom