Baryon acoustic oscillations at z = 2.34 from the correlations of Ly$α$ absorption in eBOSS DR14 (1904.03400v2)

Abstract: 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 $D_H(2.34)/r_d=8.86\pm 0.29$ and $D_M(2.34)/r_d=37.41\pm 1.86$, 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.

Baryon Acoustic Oscillations from Lyα Absorption in eBOSS DR14

This paper investigates the measurement of baryon acoustic oscillations (BAO) using Lyα absorption in quasar spectra from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) in Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS-IV). Utilizing 179,965 quasar spectra in the Lyα absorption region and 56,154 spectra in the Lyβ region, the paper measures cosmological distances at an effective redshift of z=2.34. This provides insights into the Universe's expansion history, complementing other BAO methodologies that employ galaxies and quasars as discrete tracers of cosmic structures.

Measurement and Methodology

The research utilizes both Lyα and Lyβ absorption lines in quasar spectra to enhance the statistical power of BAO detection. This paper introduces a refined physical model to account for correlations outside the BAO peak and to manage absorptions in the Lyman-β region. The data analysis relies heavily on constructing a precise flux-transmission field, δq(λ), which measures variations around an average transmitted flux spectrum using an assessment of continuum uncertainties and high column density (HCD) absorptions.

The correlation function is meticulously derived by correlating flux fluctuations as a function of angular and radial separations. A significant challenge addressed is the contamination from intergalactic metals, and the paper extensively models these effects to ensure accurate detection of the BAO feature.

Results

The paper yields measurements of the Hubble distance, $D_H$, and the comoving angular diameter distance, $D_M$, relative to the sound horizon at the drag epoch, $r_d$. The results are $D_H(2.34)/r_d=8.86±0.29$ and $D_M(2.34)/r_d=37.41±1.86$, which are in agreement with predictions from the flat-ΛCDM model supported by Cosmic Microwave Background (CMB) data.

Implications

These measurements, particularly the combination of Lyα and Lyβ regions, contribute to sharpening the constraints on the Universe's expansion history and dark energy models. The results are consistent with the ΛCDM model and reinforce the utility of BAO measurements in high redshift regimes, facilitating cross-validation of cosmological parameters estimated from CMB observations. The paper highlights that the combined analysis with quasar-Lyα absorption cross-correlation strengthens the robustness of the cosmological model, remaining consistent within 1.7σ of the ΛCDM predictions.

Future Perspectives

eBOSS DR14 represents a step towards improved precision in BAO measurements, a critical endeavor as the upcoming DESI and WEAVE-QSO surveys prepare to deliver even more comprehensive datasets. Future analyses will focus on minimizing systematic uncertainties, such as those posed by metal line absorptions and continuum fitting biases, ultimately aiming to uncover finer details of the Universe's expansion dynamics.

In summary, this paper establishes the effectiveness of using the Lyα forest in studying cosmological distances and underscores the role of advanced modeling techniques in interpreting complex astronomical data. The findings remain instrumental in strengthening the empirical foundation for our understanding of the Universe's structural evolution.