arXiv subjects

C. Fechner

Publications and source records attributed to C. Fechner.

23 records · Page 2Linked to original sources

arXiv2005

Nitrogen-deficient and iron-rich associated absorbers with oversolar metallicities towards the quasar HE0141-3932

HE0141-3932 (zem=1.80) is a bright blue radio-quite quasar which reveals an emission line spectrum with an unusually weak Ly-alpha line. In addition, large redshift differences (Delta z=0.05) are observed between high ionization and low ionization emission lines. Absorption systems identified at z=1.78, 1.71, and 1.68 show mild oversolar metallicities (Z ~= 1-2Zsolar) and can be attributed to the associated gas clouds ejected from the circumnuclear region. The joint analysis of the emission and absorption lines leads to the conclusion that this quasar is seen almost pole-on. Its apparent luminosity may be Doppler boosted by ~10 times. The absorbing gas shows high abundance of Fe, Mg, and Al ([Fe, Mg, Al/C] ~= 0.15+/-0.10) along with underabundance of N ([N/C]<=-0.5). This abundance pattern is at variance with current chemical evolution models of QSOs predicting [N/C]>0 and [Fe/C]<0 at Z ~ Zsolar. Full details of this work are given in Reimers et al. (2005).

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arXiv2005

HE 0141-3932: a bright QSO with an unusual emission line spectrum and associated absorption

HE 0141-3932 (zem = 1.80) is a bright blue radio-quite quasar with an unusually weak Ly-alpha emission line. Large redshift differences (Delta z = 0.05) are observed between high ionization and low ionization emission lines. Absorption systems identified at zabs = 1.78, 1.71, and 1.68 show mild oversolar metallicities (Z ~= 1-2Zsolar) and can be attributed to the associated gas clouds ejected from the circumnuclear region. The joint analysis of the emission and absorption lines leads to the conclusion that this quasar is seen almost pole-on. Its apparent luminosity may be Doppler boosted by ~10 times. The absorbing gas shows a high abundance of Fe, Mg and Al ([Fe, Mg, Al/C] ~= 0.15 +/- 0.10) along with underabundance of N ([N/C] <= -0.5). This abundance pattern is at variance with current chemical evolution models of QSOs predicting [N/C] >= 0$ and [Fe/C] < 0 at Z ~ Zsolar.

astro-ph↗

arXiv2004

A Concordance Model of the Lyman-alpha Forest at z = 1.95

We present 40 fully hydrodynamical numerical simulations of the intergalactic gas that gives rise to the Ly-alpha forest. We make artificial spectra from each and measure three output parameters: the mean flux, a measure of the most common Ly-alpha line width (b-value), and the 1D power spectrum of the flux on scales from 0.01 - 0.1 s/km. We investigate how these output parameters are correlated with the input parameters that describe the simulations. These input parameters include the main cosmological parameters; and two astrophysical parameters gammah and gammahe. The parameter gammah controls the rate of ionization of H I, He I and He II while gammahe controls the rate of heating. We compare the output from the simulations to data from HIRES and UVES spectra and we give a new measurement of the flux power from these spectra at z=1.95. We find that simulations with a wide variety of sigma_8 values, from at least 0.8 - 1.1, can fit the small scale flux power and b-values when we adjust gammahe to compensate for the sigma_8 change. We can also use gammah to adjust the H I ionization rate to simultaneously match the mean flux. We derive scaling relations that give the output parameter values expected for a variety of input parameters with errors of 2% for optical depth and 1.4% for b-balues. We can break the degeneracy between gammahe and sigma_8 using large scale power or other data to fix sigma_8.

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arXiv2004

The HeII Lyman alpha forest: evaluation of simulated data

Using an artificial HI Lyman alpha spectrum we simulate the corresponding HeII forest with fixed values of eta and a Doppler parameter consisting of a thermal and a turbulent part. In addition metal lines with line strengths and line density as expected in the case of HS 1700+6416 are superimposed. FUSE-like noise is added. The analysis of the simulated spectra in terms of Doppler profiles recovers the input eta = N(HeII)/N(HI) with a scatter by a factor of 10. About 10 % have significantly lower eta-values for various reasons. The majority of the extremely high eta-values (up to 1000) are evidently caused by metal lines. We conclude that part of the scatter in eta of previous analyses of the HeII forest in HE 2347-4342 can be regarded as an artifact. However, we confirm that the correlation between small column densities (in voids) and high eta-values is not a methodical artifact and appears to be a true phenomenon.

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arXiv2004

FUSE observations of the HeII Lyman alpha forest towards HS1700+6416

We present FUSE observations of the HeII Lyman alpha forest in the redshift range 2.3 < z < 2.7 towards HS1700+6416. Between October 2002 and February 2003, the brightness of the QSO increased by a factor 2. Therefore, with an exposure time of 203 ks during orbital night, the quality of the resulting spectrum is comparable to the HE2347-4342 data. This second line of sight with a resolved HeII Lyman alpha forest reveals a similar variation of several orders of magnitude of the column density ratio eta = N(HeII)/N(HI) and confirms the results of previous studies. The well-known metal line spectrum of HS1700+6416 permits to examine the influence of metal line absorption on the HeII column densities.

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