Measurement of BAO correlations at $z=2.3$ with SDSS DR12 \lya-Forests (1702.00176v2)

Abstract: 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 paper presents a robust measurement of BAO correlations at z=2.3 using 157,783 quasar Lyα spectra to establish key cosmological benchmarks.
• It employs advanced modeling of flux transmission with rigorous systematic error checks for metal absorptions, HCDs, and pipeline noise.
• The results yield precise constraints on the Hubble parameter and distance measures, reinforcing flat-Lambda CDM predictions with a 5.2σ BAO detection.

Measurement of Baryon Acoustic Oscillation Correlations at z=2.3 with SDSS DR12 Lyα-Forests

This paper presents an analysis of the baryon acoustic oscillations (BAO) using the Lyα forest observed in the Sloan Digital Sky Survey (SDSS) DR12. The paper utilizes a data set derived from 157,783 quasars within a redshift range of 2.1 to 3.5. The main objective of the investigation is to measure the BAO peak positions and derive cosmological parameters by examining the autocorrelation function of the flux-transmission field in the Lyα forests.

Methodology

The analysis involves estimating the correlation function from the transmitted flux fraction, while constructing a physical model that accurately describes the various correlation contributions, including those from Lyα absorption, metal absorptions, and high-column-density systems (HCDs). Notably, the authors have improved upon previous studies by implementing a comprehensive range of systematic error checks, enhancing the spectroscopic data extraction and handling pipeline noise.

Key parameters are determined by fitting the measured correlation function to the model. The fits yield constraints on the comoving angular diameter distance, $D_M(z=2.33)/r_d$, and the Hubble distance, $D_H(z=2.33)/r_d$, relative to the sound horizon at the drag epoch, $r_d$.

Results

The Hubble parameter determined in this paper is $D_H(z=2.33)/r_d=9.07 \pm 0.31$, and the combination of $D_H^{0.7}D_M^{0.3}/r_d=13.94 \pm 0.35$, aligns well with predictions from flat-Lambda CDM models, consistent with cosmic microwave background observations. The overall constraints on BAO parameters suggest a universe with a low curvature, fitting within open-$Λ$ models with density parameters $\Omega_m = 0.296 \pm 0.029$ and $\Omega_\Lambda = 0.699 \pm 0.100$.

Discussion

The implications of these measurements are significant for cosmology as they reinforce the concordance cosmology model. The precision of these measurements, although not superseding that of lower redshift galaxy surveys, provides important constraints on models of cosmic expansion. Furthermore, the analysis advances the field's understanding of non-galactic BAO measurements, especially in the context of utilizing quasar absorption lines.

The paper provides a thorough investigation into potential systematic errors, including those induced by the data pipeline and those inherent to the astrophysical phenomena themselves, such as fluctuations in the ionizing ultraviolet background. With these considerations, the evidence for BAO at $z=2.3$ is demonstrated with a statistical significance of $5.2\sigma$.

Future Directions

Future surveys, such as DESI, aim to enhance the statistical power and precision of such measurements. An improved understanding of non-linear effects, as well as the inclusion of cross-correlation studies with quasars, will enable more robust parameter constraints and further insights into the cosmic expansion and the nature of dark energy. The methodologies refined here will be critical in realizing these ambitions and ensuring the reliability of future high-redshift universe probes.