Toward unbiased determination of the redshift evolution of Lyman-alpha forest clouds

Abstract

view Abstract Citations (12) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Toward Unbiased Determination of the Redshift Evolution of Lyman-Alpha Forest Clouds Lu, Limin ; Zuo, Lin Abstract The possibility of using D_A_, the mean depression of a quasar spectrum due to Lyα forest absorption, to study the number density evolution of the Lyα forest clouds is examined in some detail. Current D_A_ measurements are made against a continuum that is a power- law extrapolation from the continuum longward of Lyα emission. Compared to the line-counting approach, the D_A_-method has the advantage that the D_A_ measurements are not affected by line-blending effects. However, we find using low-redshift quasar spectra obtained with the Hubble Space Telescope (HST), where the true continuum in the Lyα forest can be estimated fairly reliably because of the much lower density of the Lyα forest lines, that the extrapolated continuum often deviates systematically from the true continuum in the forest region. Such systematic continuum errors introduce large errors in the D_A_ measurements. The current D_A_ measurements may also be significantly biased by the possible presence of the Gunn-Peterson absorption. We propose a modification to the existing D_A_-method, namely, to measure D_A_ against a locally established continuum in the Lyα forest. Under conditions that the quasar spectrum has good resolution and S/N to allow for a reliable estimate of the local continuum in the Lyα forest, the modified D_A_ measurements should be largely free of the systematic uncertainties suffered by the existing D_A_ measurements. We also introduce a formalism based on the work of Zuo (1993) to simplify the application of the D_A_-method(s) to real data. We discuss the merits and limitations of the modified D_A_-method, and conclude that it is a useful alternative. Our findings that the extrapolated continuum from longward of Lyα emission often deviates systematically from the true continuum in the Lyα forest present a major problem in the study of the Gunn- Peterson absorption. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/174086 Bibcode: 1994ApJ...426..502L Keywords: Absorption Spectra; Intergalactic Media; Line Spectra; Lyman Alpha Radiation; Quasars; Red Shift; Spectrum Analysis; Bias; Cosmology; Errors; Estimates; Evolution (Development); Astronomy; COSMOLOGY: OBSERVATIONS; GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS | data products SIMBAD (7) NED (7) MAST (1) ESA (1)