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Register a new userBaryon acoustic oscillations from the complete SDSS-III Ly$alpha$-quasar cross-correlation function at $z=2.4$
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H\\'elion Du Mas Des Bourboux
Publication date
2017
fields
Physics
and research's language is
English
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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 $1.8sigma$ 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 $2.3sigma$ of the same flat-$Lambda$CDM model.
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The 2-point angular correlation function $w(theta)$ (2PACF), where $theta$ is the angular separation between pairs of galaxies, provides the transversal Baryon Acoustic Oscillation (BAO) signal almost model-independently. In this paper we use 409,337 luminous red galaxies in the redshift range $z = [0.440,0.555]$ obtained from the tenth data release of the Sloan Digital Sky Survey (SDSS DR10) to estimate $theta_{rm{BAO}}(z)$ from the 2PACF at six redshift {shells}. Since noise and systematics can hide the BAO signature in the $w - theta$ plane, we also discuss some criteria to localize the acoustic bump. We identify two sources of model-dependence in the analysis, namely, the value of the acoustic scale from Cosmic Microwave Background (CMB) measurements and the correction in the $theta_{rm{BAO}}(z)$ position due to projection effects. Constraints on the dark energy equation-of-state parameter w$(z)$ from the $theta_{rm{BAO}}(z)$ diagram are derived, as well as from a joint analysis with current CMB measurements. We find that the standard $Lambda$CDM model as well as some of its extensions are in good agreement with these $theta_{rm{BAO}}(z)$ measurements.
We present a measurement of the baryon acoustic oscillation (BAO) scale at redshift $z=2.35$ from the three-dimensional correlation of Lyman-$alpha$ (Ly$alpha$) forest absorption and quasars. The study uses 266,590 quasars in the redshift range $1.77<z<3.5$ from the Sloan Digital Sky Survey (SDSS) Data Release 14 (DR14). The sample includes the first two years of observations by the SDSS-IV extended Baryon Oscillation Spectroscopic Survey (eBOSS), providing new quasars and re-observations of BOSS quasars for improved statistical precision. Statistics are further improved by including Ly$alpha$ absorption occurring in the Ly$beta$ wavelength band of the spectra. From the measured BAO peak position along and across the line of sight, we determined the Hubble distance $D_{H}$ and the comoving angular diameter distance $D_{M}$ relative to the sound horizon at the drag epoch $r_{d}$: $D_{H}(z=2.35)/r_{d}=9.20pm 0.36$ and $D_{M}(z=2.35)/r_{d}=36.3pm 1.8$. These results are consistent at $1.5sigma$ with the prediction of the best-fit spatially-flat cosmological model with the cosmological constant reported for the Planck (2016) analysis of cosmic microwave background anisotropies. Combined with the Ly$alpha$ auto-correlation measurement presented in a companion paper, the BAO measurements at $z=2.34$ are within $1.7sigma$ of the predictions of this model.
The clustering properties of the Universe at large-scales are currently being probed at various redshifts through several cosmological tracers and with diverse statistical estimators. Here we use the three-point angular correlation function (3PACF) to probe the baryon acoustic oscillation (BAO) features in the quasars catalogue from the twelfth data release of the Sloan Digital Sky Survey, with mean redshift z = 2.225, detecting the BAO imprint with a statistical significance of 2.9{sigma}, obtained using lognormal mocks. Following a quasi model-independent approach for the 3PACF, we find the BAO transversal signature for triangles with sides $theta_1 = 1.0^circ$ and $theta_2 = 1.5^circ$ and the angle between them of $alpha = 1.59 pm 0.17$ rad, a value that corresponds to the angular BAO scale ${theta}_{BAO} = 1.82^circ pm 0.21^circ$ , in excellent agreement with the value found in a recent work (${theta}_{BAO} = 1.77^circ pm 0.31^circ$ ) applying the 2PACF to similar data. Moreover, we performed two type of tests: one to confirm the robustness of the BAO signal in the 3PACF through random displacements in the dataset, and the other to verify the suitability of our random samples, a null test that in fact does not show any signature that could bias our results.
We measure the imprint of primordial baryon acoustic oscillations (BAO) in the correlation function of Ly$alpha$ absorption in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) and the extended BOSS (eBOSS) in Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS)-IV. In addition to 179,965 spectra with absorption in the Lyman-$alpha$ (Ly$alpha$) region, we use, for the first time, Ly$alpha$ absorption in the Lyman-$beta$ region of 56,154 spectra. We measure the Hubble distance, $D_H$, and the comoving angular diameter distance, $D_M$, relative to the sound horizon at the drag epoch $r_d$ at an effective redshift $z=2.34$. Using a physical model of the correlation function outside the BAO peak, we find $D_H(2.34)/r_d=8.86pm 0.29$ and $D_M(2.34)/r_d=37.41pm 1.86$, within 1$sigma$ from the flat-$Lambda$CDM model consistent with CMB anisotropy measurements. With the addition of polynomial broadband terms, the results remain within one standard deviation of the CMB-inspired model. Combined with the quasar-Ly$alpha$ cross-correlation measurement presented in a companion paper Blomqvist19, the BAO measurements at $z=2.35$ are within 1.7$sigma$ of the predictions of this model.
Following a quasi model-independent approach we measure the transversal BAO mode at high redshift using the two-point angular correlation function (2PACF). The analyses done here are only possible now with the quasar catalogue from the twelfth data release (DR12Q) from the Sloan Digital Sky Survey, because it is spatially dense enough to allow the measurement of the angular BAO signature with moderate statistical significance and acceptable precision. Our analyses with quasars in the redshift interval z = [2.20,2.25] produce the angular BAO scale theta_BAO = 1.77 +- 0.31 deg with a statistical significance of 2.12 sigma (i.e., 97% confidence level), calculated through a likelihood analysis performed using the theoretical covariance matrix sourced by the analytical power spectra expected in the LCDM concordance model. Additionally, we show that the BAO signal is robust -although with less statistical significance- under diverse bin-size choices and under small displacements of the quasars angular coordinates. Finally, we also performed cosmological parameter analyses comparing the theta_BAO predictions for wCDM and w(a)CDM models with angular BAO data available in the literature, including the measurement obtained here, jointly with CMB data. The constraints on the parameters Omega_M, w_0 and w_a are in excellent agreement with the LCDM concordance model.
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