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Register a new userThe one-dimensional power spectrum from the SDSS DR14 Ly$alpha$ forests
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Nathalie Palanque-Delabrouille
Publication date
2018
fields
Physics
and research's language is
English
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We present a measurement of the 1D Ly$alpha$ forest flux power spectrum, using the complete Baryon Oscillation Spectroscopic Survey (BOSS) and first extended-BOSS (eBOSS) quasars at $z_{rm qso}>2.1$, corresponding to the fourteenth data release (DR14) of the Sloan Digital Sky Survey (SDSS). Our results cover thirteen bins in redshift from $z_{rm Lyalpha}=2.2$ to 4.6, and scales up to $k=0.02rm ,(km/s)^{-1}$. From a parent sample of 180,413 visually inspected spectra, we selected the 43,751 quasars with the best quality; this data set improves the previous result from the ninth data release (DR9), both in statistical precision (achieving a reduction by a factor of two) and in redshift coverage. We also present a thorough investigation of identified sources of systematic uncertainties that affect the measurement. The resulting 1D power spectrum of this work is in excellent agreement with the one from the BOSS DR9 data.
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We have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-$alpha$ forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from $<z> = 2.2$ to $<z> = 4.4$, and scales from 0.001 $rm(km/s)^{-1}$ to $0.02 rm(km/s)^{-1}$. We determine the methodological and instrumental systematic uncertainties of our measurements. We provide a preliminary cosmological interpretation of our measurements using available hydrodynamical simulations. The improvement in precision over previously published results from SDSS is a factor 2--3 for constraints on relevant cosmological parameters. For a $Lambda$CDM model and using a constraint on $H_0$ that encompasses measurements based on the local distance ladder and on CMB anisotropies, we infer $sigma_8 =0.83pm0.03$ and $n_s= 0.97pm0.02$ based on ion{H}{i} absorption in the range $2.1<z<3.7$.
We present a new compilation of inferences of the linear 3D matter power spectrum at redshift $z,{=},0$ from a variety of probes spanning several orders of magnitude in physical scale and in cosmic history. We develop a new lower-noise method for performing this inference from the latest Ly$alpha$ forest 1D power spectrum data. We also include cosmic microwave background (CMB) temperature and polarization power spectra and lensing reconstruction data, the cosmic shear two-point correlation function, and the clustering of luminous red galaxies. We provide a Dockerized Jupyter notebook housing the fairly complex dependencies for producing the plot of these data, with the hope that groups in the future can help add to it. Overall, we find qualitative agreement between the independent measurements considered here and the standard $Lambda$CDM cosmological model fit to the {it Planck} data
The impact of cosmic reionization on the Ly$alpha$ forest power spectrum has recently been shown to be significant even at low redshifts ($z sim 2$). This memory of reionization survives cosmological time scales because high-entropy mean-density gas is heated to $sim 3times10^4$ K by reionization, which is inhomogeneous, and subsequent shocks from denser regions. In the near future, the first measurements of the Ly$alpha$ forest 3D power spectrum will be very likely achieved by upcoming observational efforts such as the Dark Energy Spectroscopic Instrument (DESI). In addition to abundant cosmological information, these observations have the potential to extract the astrophysics of reionization from the Ly$alpha$ forest. We forecast, for the first time, the accuracy with which the measurements of Ly$alpha$ forest 3D power spectrum can place constraints on the reionization parameters with DESI. Specifically, we demonstrate that the constraints on the ionization efficiency, $zeta$, and the threshold mass for haloes that host ionizing sources, $m_{rm turn}$, will have the $1sigma$ error at the level of $zeta = 25.0 pm 11.6$ and $log_{10} (m_{rm turn}/{rm M}_odot) = 8.7^{+0.36}_{-0.70}$, respectively. The Ly$alpha$ forest 3D power spectrum will thus provide an independent probe of reionization, probably even earlier in detection with DESI, with a sensitivity only slightly worse than the upcoming 21 cm power spectrum measurement with the Hydrogen Epoch of Reionization Array (HERA), i.e. $sigma_{rm DESI} / sigma_{rm HERA} approx 1.5$ for $zeta$ and $sigma_{rm DESI}/sigma_{rm HERA} approx 2.0$ for $log_{10}(m_{rm turn} / $M$_odot)$. Nevertheless, the Ly$alpha$ forest constraint will be improved about three times tighter than the current constraint from reionization observations with high-z galaxy priors.
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.
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.
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