A new measurement of the mean transmitted flux in the Ly α and Ly β forest

Author:

Ding Jiani12,Madau Piero13,Prochaska J Xavier14

Affiliation:

1. Department of Astronomy and Astrophysics, University of California , Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 , USA

2. Department of Astronomy, Tsinghua University , Beijing 100084 , China

3. Dipartimento di Fisica ‘G. Occhialini’, Università degli Studi di Milano-Bicocca , Piazza della Scienza 3, I-20126 Milano , Italy

4. Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), 5-1-5 Kashiwanoha, Kashiwa 277-8583 , Japan

Abstract

ABSTRACT We present new measurements of the mean transmitted flux in the hydrogen $\rm {Ly\,\alpha }$ and a relative transmitted flux measurement in $\rm {Ly\,\beta }$ using 27 008 quasar spectra from the Fourteenth Data Release (DR14) of the Extended Baryon Oscillation Spectroscopic Survey. Individual spectra are first combined into 16 composites with mean redshifts in the range of $2.8\lt z\lt 4.9$. We then apply Markov Chain Monte Carlo (MCMC) inference to produce a piecewise fit of the effective $\tau _{\rm {Ly\,\alpha }}$ (corrected for metal lines and optically thick absorption) assuming a spline point distribution. We also perform a relative $\Delta \tau _{\rm {Ly\,\beta }}$ measurement with the same data set, finding $\Delta \tau _{\rm {Ly\,\beta }}\lt 0.35$ at $z\lt 4.8$. The 6–8  per cent precision measurements in the rest frame 1075–1150 Å at ${\it z} \ \lt \rm {4.0}$ and 10–12 per cent precision measurements in the same region at ${\it z} \ \gt \rm {4.0}$ on $\tau _{\rm {Ly\,\alpha }}$, and our determinations of $\Delta \tau _{\rm {Ly\,\beta }}$, are dominated by systematic errors, likely arising from bias and uncertainties in estimates of the quasar continuum. Our $\tau _{\rm {Ly\,\alpha }}$ values show a smooth increase by a factor of 5 over the redshift range $z=2.4-4.4$.

Funder

NASA

National Science Foundation of China

Publisher

Oxford University Press (OUP)

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