The Baryon Oscillation Spectroscopic Survey of SDSS-III

TL;DR

The BOSS survey (SDSS-III) targets BAO via a massive spectroscopic campaign that combines a galaxy redshift sample (LOWZ/CMASS) to z<0.7 with a dense Lyα forest quasar grid at z>2.15, enabling precise measurements of cosmic distances. It introduces an optimized target selection, tiling, and plate design, paired with a robust data-reduction pipeline, to maximize BAO signal while controlling systematics. Early DR9 results include the first 3D Lyα clustering detections and a 1.7% distance measurement at z=0.57, illustrating the method’s power and validating the survey design. The work demonstrates the potential of large-volume BAO studies to constrain dark energy and cosmology, providing a framework for future surveys that aim to map cosmic expansion across a broad redshift range.”

Abstract

The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000 quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyman alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance D_A to an accuracy of 1.0% at redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyman alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.

Figures (16)

• Figure 1: Location of pointing centers for the 2208 spectroscopic plates in the BOSS survey footprint in an Aitoff projection in J2000 equatorial coordinates. Gray circles represent the location of plates that remained to be drilled after Summer 2011. Blue circles represent plates that were drilled and were ready to observe in the third year of the survey. Red circles represent the plates that were completed in either the first or second year of the survey, whose observations are released in DR9.
• Figure 2: Image of plate 3552 immediately after the marking stage. Bundles are separated by black bounded edges, and holes are marked blue to reduce contamination between nearby emission line galaxies or quasars. Holes for guide star fibers are marked in black and denoted by the corresponding number ranging from 1-16.
• Figure 3: An example of the diagnostic from a series of four science exposures of plate 3775 that are produced in the quick reductions of data at APO. Similar plots become available to the observers less than five minutes after the end of an exposure. Left: Cumulative signal-to-noise ratio (S/N in the figure captions) as a function of $g_{\rm fib2}$ (top) and $i_{\rm fib2}$ (bottom). Fibers from the two spectrographs are indicated by the blue symbol "x" (spectrograph 1) and a magenta square (spectrograph 2). The intercept of the linear fit of log(S/N) as a function of magnitude and RMS of that fit are computed for each spectrograph separately. Only fibers with fiber2 magnitudes in the range 21-22 (20-21) for the blue (red) cameras are used in the fit as indicated by the vertical dotted lines. The slope is held fixed at $-0.3$ as empirically determined from fits to the larger sample. This magnitude range is near the region of sky-limited noise and near the faint end of the main galaxy and quasar samples for the red and blue cameras respectively. Right: The spatial profile of SNR over the plate. Red symbols represent fibers that fall below the best fit of the SNR linear solution that is represented by the solid line in the left hand panels. Green symbols represent fibers that fall above the best linear fit of the SNR solution. The size of the symbol relates to the amount by which the fiber deviates, growing larger for fibers with larger deviation from the best fit. Guiding problems or other systematics can appear as coherent structure in this diagram. The distribution of objects that fall below the best-fit line is fairly uniform, indicating a lack of such effects for this particular plate.
• Figure 4: Left: Distribution of plates in the BOSS footprint binned in 15 minute increments in Right Ascension. Right: Number of hours of observing time available as a function of LST (black line) and the simulated time required at each LST to observe the full survey (blue line). The observing time is sampled in 15 minute increments and assumes a uniformly distributed 45% efficiency after weather loss. The discrete sum of the entries under the black line is equal to 3585 hours. The final simulated LST distribution shown in blue is discussed in §\ref{['subsec:thresholds']}.
• Figure 5: The fraction of completed plates as a function of SNR$^2$ as reported by SOS. The SNR$^2$ for the first year of data is shown as a solid line while the SNR$^2$ for the simulated survey, with somewhat lower thresholds as described in §\ref{['subsec:thresholds']}, is shown as the broken line. In both cases, the SNR$^2$ for the red cameras is shown in red while the SNR$^2$ for blue cameras is shown in blue.