The Lyman-\(\beta\) forest refers to a region in the spectra of distant quasars that lies between the rest-frame Lyman-\(\beta\) and Lyman-\(\gamma\) emissions. The forest in this region is dominated ...by a combination of absorption due to resonant Ly\(\alpha\) and Ly\(\beta\) scattering. When considering the 1D Ly\(\beta\) forest in addition to the 1D Ly\(\alpha\) forest, the full statistical description of the data requires four 1D power spectra: Ly\(\alpha\) and Ly\(\beta\) auto-power spectra and the Ly\(\alpha\)-Ly\(\beta\) real and imaginary cross-power spectra. We describe how these can be measured using an optimal quadratic estimator that naturally disentangles Ly\(\alpha\) and Ly\(\beta\) contributions. Using a sample of approximately 60,000 quasar sight-lines from the BOSS Data Release 9, we make the measurement of the one-dimensional power spectrum of fluctuations due to the Ly\(\beta\) resonant scattering. While we have not corrected our measurements for resolution damping of the power and other systematic effects carefully enough to use them for cosmological constraints, we can robustly conclude the following: i) Ly\(\beta\) power spectrum and Ly\(\alpha\)-Ly\(\beta\) cross spectra are detected with high statistical significance; ii) the cross-correlation coefficient is \(\approx 1\) on large scales; iii) the Ly\(\beta\) measurements are contaminated by the associated OVI absorption, which is analogous to the SiIII contamination of the Ly\(\alpha\) forest. Measurements of the Ly\(\beta\) forest will allow extension of the usable path-length for the Ly\(\alpha\) measurements while allowing a better understanding of the physics of intergalactic medium and thus more robust cosmological constraints.
A recent SeaMARC II survey along the Hanks and crest of the East Pacific Rise between 13° and 15° N (Edwards et al., 1988) provides us with a unique opportunity to compare stochastic models of the ...seafloor against bathymetric data. Stochastic models can be used to quantitatively characterize intermediate to small‐scale (<100 km) seafloor features such as abyssal hills. In a recent paper, Goff and Jordan (1988) introduced a model for the two‐point covariance function having five free parameters which describe the amplitude, orientation, characteristic wavelengths, and Hausdorff (fractal) dimension of seafloor topography. These parameters can be estimated from multibeam data such as Sea Beam by inverting auto‐ and cross‐covariance functions for the beams. The stochastic model can be used to generate synthetic topography to arbitrary resolution and scale. By assuming appropriate Sea Beam noise and response characteristics we can use the synthetic topography to produce synthetic data sets. Comparison of real and synthetic data is an important means of assessing the performance of the stochastic model. Unfortunately, the limited spatial extent of Sea Beam in the across‐track direction and lack of 100% coverage over large areas severely limit our ability to compare the full two‐dimensional stochastic model with real seafloor morphology, especially with respect to abyssal‐hill length characteristics. The recent SeaMARC II survey included sufficient off‐axis topography (over 100 km, 70,000 km2) to permit a comparison of a complete two‐dimensional synthetic topographic field with a region of abyssal hill terrain that has close to 100% data coverage. We have estimated stochastic models for various regions of the SeaMARC II survey area from several Sea Beam tracks which cross it. Synthetic fields are generated from these models using a Fourier method. These comparisons indicate the extent to which the model succeeds in characterizing seafloor topography, and the directions we will need to take to improve our modeling. A change in ridge complexity at 14° N and the location of a propagator pseudofault appear to be correlated with changes in stochastic character modeled in this region. Such correlations may provide important new constraints on the understanding of ridge processes.
The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct novel cosmological observations using the BOSS spectrograph at Apache Point Observatory. Observations will be simultaneous ...with the Time Domain Spectroscopic Survey (TDSS) designed for variability studies and the Spectroscopic Identification of eROSITA Sources (SPIDERS) program designed for studies of X-ray sources. eBOSS will use four different tracers to measure the distance-redshift relation with baryon acoustic oscillations (BAO). Using more than 250,000 new, spectroscopically confirmed luminous red galaxies at a median redshift z=0.72, we project that eBOSS will yield measurements of \(d_A(z)\) to an accuracy of 1.2% and measurements of H(z) to 2.1% when combined with the z>0.6 sample of BOSS galaxies. With ~195,000 new emission line galaxy redshifts, we expect BAO measurements of \(d_A(z)\) to an accuracy of 3.1% and H(z) to 4.7% at an effective redshift of z= 0.87. A sample of more than 500,000 spectroscopically-confirmed quasars will provide the first BAO distance measurements over the redshift range 0.9<z<2.2, with expected precision of 2.8% and 4.2% on \(d_A(z)\) and H(z), respectively. Finally, with 60,000 new quasars and re-observation of 60,000 quasars known from BOSS, we will obtain new Lyman-alpha forest measurements at redshifts z>2.1; these new data will enhance the precision of \(d_A(z)\) and H(z) by a factor of 1.44 relative to BOSS. Furthermore, eBOSS will provide improved tests of General Relativity on cosmological scales through redshift-space distortion measurements, improved tests for non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species. Here, we provide an overview of the cosmological goals, spectroscopic target sample, demonstration of spectral quality from early data, and projected cosmological constraints from eBOSS.
We report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the \Lya forest of high-redshift quasars. The ...study uses 48,640 quasars in the redshift range \(2.1\le z \le 3.5\) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift \(z=2.3\), we measure the monopole and quadrupole components of the correlation function for separations in the range \(20\hMpc<r<200\hMpc\). A peak in the correlation function is seen at a separation equal to \((1.01\pm0.03)\) times the distance expected for the BAO peak within a concordance \(\Lambda\)CDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance \(\da\) and the expansion rate \(H\) at \(z=2.3\) that, combined with priors on \(H_0\) and the baryon density, require the existence of dark energy. Combined with constraints derived from Cosmic Microwave Background (CMB) observations, this result implies \(H(z=2.3)=(224\pm8){\rm km\,s^{-1}Mpc^{-1}}\), indicating that the time derivative of the cosmological scale parameter \(\dot{a}=H(z=2.3)/(1+z)\) is significantly greater than that measured with BAO at \(z\sim0.5\). This demonstrates that the expansion was decelerating in the range \(0.7<z<2.3\), as expected from the matter domination during this epoch. Combined with measurements of \(H_0\), one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.
We present the BOSS Lyman-alpha (Lya) Forest Sample from SDSS Data Release 9, comprising 54,468 quasar spectra with zqso > 2.15 suitable for Lya forest analysis. This data set probes the ...intergalactic medium with absorption redshifts 2.0 < z_alpha < 5.7 over an area of 3275 square degrees, and encompasses an approximate comoving volume of 20 h^-3 Gpc^3. With each spectrum, we have included several products designed to aid in Lya forest analysis: improved sky masks that flag pixels where data may be unreliable, corrections for known biases in the pipeline estimated noise, masks for the cores of damped Lya systems and corrections for their wings, and estimates of the unabsorbed continua so that the observed flux can be converted to a fractional transmission. The continua are derived using a principal component fit to the quasar spectrum redwards of restframe Lya (lambda > 1216 Ang), extrapolated into the forest region and normalized by a linear function to fit the expected evolution of the Lya forest mean-flux. The estimated continuum errors are ~5% rms. We also discuss possible systematics arising from uncertain spectrophotometry and artifacts in the flux calibration; global corrections for the latter are provided. Our sample provides a convenient starting point for users to analyze clustering in BOSS Lya forest data, and it provides a fiducial data set that can be used to compare results from different analyses of baryon acoustic oscillations in the Lya forest. The full data set is available from the SDSS-III DR9 web site.
We present the Data Release 9 Quasar (DR9Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were ...targeted as quasar candidates during the survey, are spectrocopically confirmed as quasars via visual inspection, have luminosities Miz=2<-20.5 (in a \(\Lambda\)CDM cosmology with H0 = 70 km/s/Mpc, \(\Omega_{\rm M}\) = 0.3, and \(\Omega_{\Lambda}\) = 0.7) and either display at least one emission line with full width at half maximum (FWHM) larger than 500 km/s or, if not, have interesting/complex absorption features. It includes as well, known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. This catalog contains 87,822 quasars (78,086 are new discoveries) detected over 3,275 deg\(^{2}\) with robust identification and redshift measured by a combination of principal component eigenspectra newly derived from a training set of 8,632 spectra from SDSS-DR7. The number of quasars with \(z>2.15\) (61,931) is ~2.8 times larger than the number of z>2.15 quasars previously known. Redshifts and FWHMs are provided for the strongest emission lines (CIV, CIII, MgII). The catalog identifies 7,533 broad absorption line quasars and gives their characteristics. For each object the catalog presents five-band (u,g,r,i,z) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys.
We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Ly\(\alpha\)-forest flux-transmission at a mean redshift \(z=2.40\). The measurement uses ...the complete SDSS-III data sample: 168,889 forests and 234,367 quasars from the SDSS Data Release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level allowing a more accurate measurement of this cross-correlation. We also developed the first simulations of the cross-correlation allowing us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios \(D_{H}(z=2.40)/r_{d} = 9.01 \pm 0.36\) and \(D_{M}(z=2.40)/r_{d} = 35.7 \pm 1.7\), where the errors include marginalization over the non-linear velocity of quasars and the metal - quasar cross-correlation contribution, among other effects. These results are within \(1.8\sigma\) of the prediction of the flat-\(\Lambda\)CDM model describing the observed CMB anisotropies. We combine this study with the Ly\(\alpha\)-forest auto-correlation function 2017A&A...603A..12B, yielding \(D_{H}(z=2.40)/r_{d} = 8.94 \pm 0.22\) and \(D_{M}(z=2.40)/r_{d} = 36.6 \pm 1.2\), within \(2.3\sigma\) of the same flat-\(\Lambda\)CDM model.
We use flux-transmission correlations in \Lya forests to measure the imprint of baryon acoustic oscillations (BAO). The study uses spectra of 157,783 quasars in the redshift range \(2.1\le z \le ...3.5\) from the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12). Besides the statistical improvements on our previous studies using SDSS DR9 and DR11, we have implemented numerous improvements in the analysis procedure, allowing us to construct a physical model of the correlation function and to investigate potential systematic errors in the determination of the BAO peak position. The Hubble distance, \(\DHub=c/H(z)\), relative to the sound horizon is \(\DHub(z=2.33)/r_d=9.07 \pm 0.31\). The best-determined combination of comoving angular-diameter distance, \(\DM\), and the Hubble distance is found to be \(\DHub^{0.7}\DM^{0.3}/r_d=13.94\pm0.35\). This value is \(1.028\pm0.026\) times the prediction of the flat-\lcdm model consistent with the cosmic microwave background (CMB) anisotropy spectrum. The errors include marginalization over the effects of unidentified high-density absorption systems and fluctuations in ultraviolet ionizing radiation. Independently of the CMB measurements, the combination of our results and other BAO observations determine the open-\lcdm density parameters to be \(\om=0.296 \pm 0.029\), \(\ol=0.699 \pm 0.100\) and \(\Omega_k = -0.002 \pm 0.119\).
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.
