Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra

Lenz, Dawn D.; Ayres, Thomas R.

doi:10.1086/133096

Cited by 120 publications

(73 citation statements)

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“…4 we indicate, for all performed fits, the error on the velocity dispersion ∆v FWHM and on radial velocity ∆v LOS as a function of the lines S/N. On average our uncertainties on v FWHM and v LOS follow the scaling laws expected for fitting Gaussian profiles to noisy emission-line spectra Landman et al 1982;Lenz & Ayres 1992). For reference, at our minimum S /N = 6 we have typical errors of ∆v FWHM ≈ 30 km s −1 and ∆v LOS ≈ 10 km s −1 , and at the median (mean) S/N of our data -S /N median = 22 (S /N mean = 50), we obtain ∆v FWHM ≈ 7 km s −1 (≈3 km s −1 ) and ∆v LOS ≈ 3 km s −1 (≈1 km s −1 ).…”

Section: Hα Velocity Fieldsmentioning

confidence: 70%

The Lyman alpha reference sample

Herenz

Gruyters

Orlitová

et al. 2016

A&A

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We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z ∼ 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer α (Hα) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Lyα radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope Hα and Lyman α (Lyα) images. We can conjecture a causal connection between spatially resolved Hα kinematics and Lyα photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion σ 0 , the shearing velocity v shear , and the v shear /σ 0 ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s −1 median) and low shearing velocities (65 km s −1 median). The v shear /σ 0 values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v shear /σ 0 < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Lyα properties, we find that dispersion-dominated systems show higher Lyα equivalent widths and higher Lyα escape fractions than systems with v shear /σ 0 > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Lyα radiation.

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Section: Hα Velocity Fieldsmentioning

confidence: 70%

The Lyman alpha reference sample

Herenz

Gruyters

Orlitová

et al. 2016

A&A

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“…Lenz & Ayres (1992) found this relation to be applicable independent of the noise model assumed, whether pure poissonian or with such deviations from poissonian as are found in typical astronomical instruments.…”

Section: Estimation Of Uncertaintymentioning

confidence: 70%

“…The ratio of the peak flux of each line to the RMS of the residuals at the wavelength of the line is then taken to be the signal to noise ratio at the centre of the line. The code then applies the empirical relation described by Lenz & Ayres (1992) for estimating the uncertainty on a line fit based on the signal to noise ratio at the centre of a line. The relation is…”

Section: Estimation Of Uncertaintymentioning

confidence: 99%

alfa: an automated line fitting algorithm

Wesson

2016

Mon. Not. R. Astron. Soc.

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I present the Automated Line Fitting Algorithm, ALFA, a new code which can fit emission line spectra of arbitrary wavelength coverage and resolution, fully automatically. In contrast to traditional emission line fitting methods which require the identification of spectral features suspected to be emission lines, ALFA instead uses a list of lines which are expected to be present to construct a synthetic spectrum. The parameters used to construct the synthetic spectrum are optimised by means of a genetic algorithm. Uncertainties are estimated using the noise structure of the residuals.An emission line spectrum containing several hundred lines can be fitted in a few seconds using a single processor of a typical contemporary desktop or laptop PC. I show that the results are in excellent agreement with those measured manually for a number of spectra. Where discrepancies exist, the manually measured fluxes are found to be less accurate than those returned by ALFA. Together with the code NEAT (Wesson et al. 2012), ALFA provides a powerful way to rapidly extract physical information from observations, an increasingly vital function in the era of highly multiplexed spectroscopy. The two codes can deliver a reliable and comprehensive analysis of very large datasets in a few hours with little or no user interaction.

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“…9 In the subsequent fits, the line FWHMs were fixed at these values. Line features were fitted as Gaussians, with central wavelength and peak amplitude allowed to vary; errors were determined using the formula- tions of Lenz & Ayres (1992). We used the solar photospheric abundances of Grevesse & Sauval (1998.…”

Section: Determining Abundances and The Emission Measure Distributionmentioning

confidence: 99%

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Osten

Ayres

Brown

et al. 2003

ApJ

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We present the results of a coordinated observing campaign on the short-period RS CVn binary 2 Coronae Borealis (F6V þ G0V; P orb ¼ 1:14 days) with the Very Large Array, the Extreme Ultraviolet Explorer, and the Chandra X-Ray Observatory High-Energy Transmission Grating Spectrometer. The radio emission is consistent with previously determined quiescent gyrosynchrotron properties. Multiple flares were seen with Extreme Ultraviolet Explorer, five occurring within two consecutive orbital periods. The first of these flares was observed with Chandra. The Chandra observations of 2 CrB showed no systematic variations of line fluxes, widths, or Doppler shifts with orbital phase, nor any response in line width or offset due to the flare. This is consistent with both stars being equally active coronal emitters. We have developed a self-consistent method of spectral analysis to derive information from the line and continuum emissions concerning the distribution of plasma with temperature and elemental abundances. A bimodal temperature distribution is appropriate for both quiescent and flare intervals, with a stable peak at 6-8 MK and another variable enhancement at higher temperatures, with evidence for significant contribution from temperatures up to 50 MK during the flare, compared to 30 MK during quiescence. The iron abundance is subsolar during quiescence but is enriched by about a factor of 2 during a large flare seen with Chandra. The noble gas elements neon and argon show elevated abundances with respect to iron, but there is no clear evidence for any first ionization potential-based abundance pattern during quiescence or the flare. We have determined coronal electron densities from the helium-like ions O vii, Ne ix, Mg xi, and Si xiii, which imply densities !10 10 cm À3 . There is a small enhancement in the electron densities derived for the flare, but it is not statistically significant. We call attention to electron temperature constraints provided by the ratios of 1s 2 1 S 0 -1snp 1 P 1 transitions of the helium-like ions O vii, Ne ix, Mg xi, and Si xiii. The derived coronal electron pressures change by 1-2 orders of magnitude over a 25% change in temperature, implying nonisobaric coronal conditions. We find no evidence for significant departures from the effectively thin coronal assumption. The electron densities inferred from the soft X-ray spectra are inconsistent with cospatial gyrosynchrotron emission; further observations are necessary to discriminate the relative locations of the radio and soft X-ray-emitting plasma.

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Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra

Abstract: Landman et al. developed prescriptions to predict profile fitting errors for Gaussian emission lines perturbed by white noise. We show that their scaling laws can be generalized to more complicated signal-dependent "noise models" of common astronomical detector systems.

Cited by 120 publications

References 3 publications

The Lyman alpha reference sample

The Lyman alpha reference sample

alfa: an automated line fitting algorithm

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

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Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra

Abstract: Landman et al. developed prescriptions to predict profile fitting errors for Gaussian emission lines perturbed by white noise. We show that their scaling laws can be generalized to more complicated signal-dependent "noise models" of common astronomical detector systems.

Cited by 120 publications

References 3 publications

The Lyman alpha reference sample

The Lyman alpha reference sample

alfa: an automated line fitting algorithm

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ2Coronae Borealis

Contact Info

Product

Resources

About

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis