Mean-flux Regulated PCA Continuum Fitting of SDSS Lyman-alpha Forest Spectra

Abstract

Continuum fitting is an important aspect of Lyman-alpha forest science, since errors in the estimated optical depths scale with the fractional continuum error. However, traditional methods of estimating continua in noisy and moderate-resolution spectra (S/N < 10 pixel^-1 and R ~ 2000, respectively, such as SDSS) using power-law extrapolation or the mean spectrum, achieve no better than ~ 10-15% RMS accuracy. To improve on this, we introduce mean-flux regulated/principal component analysis (MF-PCA) continuum fitting. In this technique, PCA fitting is carried out redwards of the quasar Lyman-alpha line in order to provide a prediction for the shape of the Lyman-alpha forest continuum. The slope and amplitude of this continuum prediction is then corrected using external constraints for the Lyman-alpha forest mean-flux. From tests on mock spectra, we find that MF-PCA reduces the errors to 8% RMS in S/N ~ 2 spectra, and < 5% RMS in spectra with S/N > 5. The residual Fourier power in the continuum is decreased by a factor of a few in comparison with dividing by the mean continuum, enabling Lyman-alpha flux power spectrum measurements to be extended to ~2x larger scales. Using this new technique, we make available continuum fits for 12,069 z>2.3 Lyman-alpha forest spectra from SDSS DR7 for use by the community. This technique is also applicable to future releases of the ongoing BOSS survey, which is obtaining spectra for ~ 150,000 Lyman-alpha forest spectra at low signal-to-noise (S/N ~ 2).

14 pages; 11 figures; submitted to AJ. Continua publicly available via anonymous FTP or Data Conservancy repository

References in corpus (9)

• SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
• A Catalog of Quasar Properties from SDSS DR7
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• A Direct Precision Measurement of the Intergalactic Lyman-alpha Opacity at 2<z<4.2
• A strong redshift dependence of the broad absorption line quasar fraction
• Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-alpha forest
• A Principal Component Analysis of quasar UV spectra at z~3
• The Probability Distribution of the Lya transmitted flux from a sample of SDSS quasars
• Threshold Clustering Functions and Thermal Inhomogeneities in the Lyman-Alpha Forest

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