Simulation analysis of Lyα forest spectra. I. Empirical description at z ≈ 3

Adam Dobrzycki, Jill Bechtold

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

We present moderate-resolution (∼50 km s-1 FWHM) spectra of the Lyα forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Lyα clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN ∝ N and dN/db ∝ exp [-(b - 〈6〉)2/2 σb2], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive β = 1.4 ± 0.1 for N ranging from 1013 to 1016 cm-2 and 〈b〉 = 30 ± 15 km s-1. Most previous studies based on line lists indicated β = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for 〈b〉, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind.

Original languageEnglish (US)
Pages (from-to)102-110
Number of pages9
JournalAstrophysical Journal
Volume457
Issue number1 PART I
StatePublished - 1996

Fingerprint

simulation
quasars
flattening
absorption spectrum
lists
signal-to-noise ratio
spectrographs
density distribution
analysis
counting
signal to noise ratios
sampling
grids
distribution
telescopes
hydrogen
mirrors
wavelength
absorption spectra
parameter

Keywords

  • Cosmology: observations
  • Intergalactic medium
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Simulation analysis of Lyα forest spectra. I. Empirical description at z ≈ 3. / Dobrzycki, Adam; Bechtold, Jill.

In: Astrophysical Journal, Vol. 457, No. 1 PART I, 1996, p. 102-110.

Research output: Contribution to journalArticle

@article{51543df5ba3b4728aa65b5a6be4de37a,
title = "Simulation analysis of Lyα forest spectra. I. Empirical description at z ≈ 3",
abstract = "We present moderate-resolution (∼50 km s-1 FWHM) spectra of the Lyα forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Lyα clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN ∝ N-β and dN/db ∝ exp [-(b - 〈6〉)2/2 σb2], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive β = 1.4 ± 0.1 for N ranging from 1013 to 1016 cm-2 and 〈b〉 = 30 ± 15 km s-1. Most previous studies based on line lists indicated β = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for 〈b〉, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind.",
keywords = "Cosmology: observations, Intergalactic medium, Quasars: absorption lines",
author = "Adam Dobrzycki and Jill Bechtold",
year = "1996",
language = "English (US)",
volume = "457",
pages = "102--110",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 PART I",

}

TY - JOUR

T1 - Simulation analysis of Lyα forest spectra. I. Empirical description at z ≈ 3

AU - Dobrzycki, Adam

AU - Bechtold, Jill

PY - 1996

Y1 - 1996

N2 - We present moderate-resolution (∼50 km s-1 FWHM) spectra of the Lyα forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Lyα clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN ∝ N-β and dN/db ∝ exp [-(b - 〈6〉)2/2 σb2], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive β = 1.4 ± 0.1 for N ranging from 1013 to 1016 cm-2 and 〈b〉 = 30 ± 15 km s-1. Most previous studies based on line lists indicated β = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for 〈b〉, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind.

AB - We present moderate-resolution (∼50 km s-1 FWHM) spectra of the Lyα forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Lyα clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN ∝ N-β and dN/db ∝ exp [-(b - 〈6〉)2/2 σb2], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive β = 1.4 ± 0.1 for N ranging from 1013 to 1016 cm-2 and 〈b〉 = 30 ± 15 km s-1. Most previous studies based on line lists indicated β = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for 〈b〉, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind.

KW - Cosmology: observations

KW - Intergalactic medium

KW - Quasars: absorption lines

UR - http://www.scopus.com/inward/record.url?scp=0008131555&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0008131555&partnerID=8YFLogxK

M3 - Article

VL - 457

SP - 102

EP - 110

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 PART I

ER -