Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe BOSS-WiggleZ overlap region I: Baryon Acoustic Oscillations
487
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the large-scale clustering of galaxies in the overlap region of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS sample and the WiggleZ Dark Energy Survey. We calculate the auto-correlation and cross-correlation functions in the overlap region of the two datasets and detect a Baryon Acoustic Oscillation (BAO) signal in each of them. The BAO measurement from the cross-correlation function represents the first such detection between two different galaxy surveys. After applying density-field reconstruction we report distance-scale measurements $D_V r_s^{rm fid} / r_s = (1970 pm 47, 2132 pm 67, 2100 pm 200)$ Mpc from CMASS, the cross-correlation and WiggleZ, respectively. We use correlated mock realizations to calculate the covariance between the three BAO constraints. The distance scales derived from the two datasets are consistent, and are also robust against switching the displacement fields used for reconstruction between the two surveys. This approach can be used to construct a correlation matrix, permitting for the first time a rigorous combination of WiggleZ and CMASS BAO measurements. Using a volume-scaling technique, our result can also be used to combine WiggleZ and future CMASS DR12 results. Finally, we use the cross-correlation function measurements to show that the relative velocity effect, a possible source of systematic uncertainty for the BAO technique, is consistent with zero for our samples.
rate research
Read More
The anisotropic galaxy 2-point correlation function (2PCF) allows measurement of the growth of large-scale structures from the effect of peculiar velocities on the clustering pattern. We present new measurements of the auto- and cross- correlation function multipoles of 69,180 WiggleZ and 46,380 BOSS-CMASS galaxies sharing an overlapping volume of ~0.2 (Gpc/h)^3. Analysing the redshift-space distortions (RSD) of galaxy 2-point statistics for these two galaxy tracers, we test for systematic errors in the modelling depending on galaxy type and investigate potential improvements in cosmological constraints. We build a large number of mock galaxy catalogues to examine the limits of different RSD models in terms of fitting scales and galaxy type, and to study the covariance of the measurements when performing joint fits. For the galaxy data, fitting the monopole and quadrupole of the WiggleZ 2PCF on scales 24<s<80 Mpc/h produces a measurement of the normalised growth rate $fsigma_8$(z=0.54)=0.409$pm$0.059, whereas for the CMASS galaxies we found a consistent constraint of $fsigma_8$(z=0.54)=0.466$pm$0.074. When combining the measurements, accounting for the correlation between the two surveys, we obtain $fsigma_8$(z=0.54)=0.413$pm$0.054, in agreement with the LCDM-GR model of structure growth and with other survey measurements.
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 $2.1le z le 3.5$ 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 $20hMpc<r<200hMpc$. A peak in the correlation function is seen at a separation equal to $(1.01pm0.03)$ 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 $H(z=2.3)=(224pm8){rm km,s^{-1}Mpc^{-1}}$, 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 $zsim0.5$. 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 report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly{alpha} forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1le z le 3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28pm0.65(1sigma)^{+2.8}_{-1.2}(2sigma)$ and $D_H/r_d=9.18pm0.28(1sigma)pm0.6(2sigma)$ where $D_H=c/H$. The optimal combination, $sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $sim2%$. For the value $r_d=147.4~{rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662pm96(1sigma)~{rm Mpc}$ and $H(z=2.34)=222pm7(1sigma)~{rm km,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly{alpha} forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $Lambda$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $approx 2.5sigma$.
We present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey. We combine our correlation function with lower-redshift measurements from the 6-degree Field Galaxy Survey and Sloan Digital Sky Survey, producing a stacked survey correlation function in which the statistical significance of the detection of the baryon acoustic peak is 4.9-sigma relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) dataset comprising six distance-redshift data points, and compare the results to similar fits to the latest compilation of supernovae (SNe) and Cosmic Microwave Background (CMB) data. The BAO and SNe datasets produce consistent measurements of the equation-of-state w of dark energy, when separately combined with the CMB, providing a powerful check for systematic errors in either of these distance probes. Combining all datasets we determine w = -1.03 +/- 0.08 for a flat Universe, consistent with a cosmological constant model. Assuming dark energy is a cosmological constant and varying the spatial curvature, we find Omega_k = -0.004 +/- 0.006.
Baryon Acoustic Oscillations (BAO) are frozen relics left over from the pre-decoupling universe. They are the standard rulers of choice for 21st century cosmology, providing distance estimates that are, for the first time, firmly rooted in well-understood, linear physics. This review synthesises current understanding regarding all aspects of BAO cosmology, from the theoretical and statistical to the observational, and includes a map of the future landscape of BAO surveys, both spectroscopic and photometric.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
