scholarly journals Evolution of the EUV Background from Quasar Absorption Line Studies

1996 ◽  
Vol 168 ◽  
pp. 237-244
Author(s):  
Jill Bechtold
Keyword(s):  
Ionizing Radiation ◽  
Absorption Line ◽  
Radiation Field ◽  
Proximity Effect ◽  
Reasonable Agreement ◽  
Extreme Ultraviolet ◽  
High Redshift ◽  
Absorption Lines ◽  
Quasar Absorption Lines ◽  
Quasar Spectra

The integrated extreme ultraviolet (EUV) radiation from quasars and other high redshift sources provides an ambient ionizing radiation field which may photoionize the gas seen as quasar absorption lines. In particular, the observed evolution of the Lyα forest clouds probably results in part from the evolution of the EUV metagalactic field. Estimates of the EUV field as a function of redshift can be made from measuring the “proximity effect” in quasar spectra; uncertainties in these estimates may be large. Given the uncertainties, the estimated EUV field at z≈3 derived from the proximity effect is in reasonable agreement with the expected contribution from luminous quasars.

scholarly journals Limits on the Variation of Physical Constants Derived from Molecular Absorption Lines

1999 ◽  
Vol 183 ◽  
pp. 167-167 ◽  
Author(s):  
T. Wiklind ◽  
F. Combes
Keyword(s):  
Absorption Line ◽  
High Redshift ◽  
Absorption Lines ◽  
Frequency Resolution ◽  
Radio Lines ◽  
Molecular Absorption ◽  
Diagnostic Application ◽  
Physical Constants ◽  
Resonance Transitions ◽  
Electronic Resonance

A potential diagnostic application of molecular rotational absorption lines at high redshift is to test the invariance of physical constants. This can be done by comparing the observed redshifted frequency of a molecular absorption line with redshifted lines from other types of transitions such as the 21cm hyperfine transition or electronic resonance transitions. In order to set stringent limits, it is necessary to achieve the greatest possible frequency resolution. This makes radio lines well suited for this purpose.

scholarly journals Absorption Systems in High Redshift QSOs

1977 ◽  
Vol 74 ◽  
pp. 193-222 ◽  
Author(s):  
A. Boksenberg
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
High Redshift ◽  
Ground Level ◽  
Emission Lines ◽  
Absorption Lines ◽  
Absorption System ◽  
Characteristic Emission

In addition to the characteristic emission lines, absorption lines frequently are seen in the spectra of QSOs, usually those with high redshift (zem ≳ 1.8). About 10 percent of all QSOs listed in the compilation of Burbidge et al. (1976a) are recorded as having at least one ‘identified’ absorption system, meaning that a pattern of several selected observed lines can be matched with the apparent wavelengths of transitions (generally from the ground level) in a physical plausible group of atoms or ions at the same, although arbitrary, redshift (Bahcall 1968, Aaronson et al. 1975). Identified absorption line redshifts range from being comparable with the associated emission line redshifts, to having very much smaller values with relative velocities exceeding 0.5c in the QSO frame. Added to this, there are many QSOs having absorption lines not yet recognised as belonging to identified systems, both those objects already having one or more identifications, and others with none.

Observational estimate of the partial covering probability of quasar emission regions by distant H2 absorption clouds

2020 ◽  
Vol 493 (4) ◽  
pp. 5743-5760
Author(s):  
V V Klimenko ◽  
P Petitjean ◽  
A V Ivanchik
Keyword(s):  
High Redshift ◽  
Absorption Lines ◽  
High Spectral Resolution ◽  
Continuum Source ◽  
Partial Coverage ◽  
Reverberation Mapping ◽  
Quasar Spectra ◽  
Observational Estimate ◽  
Partial Covering ◽  
Case Part

ABSTRACT We have searched high spectral resolution spectra of quasars known to exhibit high redshift (z > 1.7) intervening H2-bearing damped Lyman-α (DLA) systems for partial coverage of the quasar emission by intervening H2 clouds. Partial coverage manifests itself by the presence of non-zero residual flux in the core of saturated H2 absorption lines. The residual flux can be observed either only at the bottom of absorption lines redshifted on top of quasar emission lines, in which case part of the broad line region (BLR) is not covered, or in all absorption lines, in case some continuum source is not covered. Among 35 H2 absorption clouds in 14 quasar spectra obtained with the VLT-UVES or Keck-HIRES spectrographs, we detect partial coverage of the BLR for 13 clouds. This result suggests that the probability of partial coverage of the QSO BLR by a distant H2 absorption cloud is about 40 per cent. For four systems towards Q 0013−0029, Q 0405−4418, Q 0812+3208, and J 2100−0641, partial coverage is detected for the first time. We determine the theoretical probability of partial coverage of the BLR by a distant H2 cloud as a function of the ratio between the cloud and the BLR sizes. Using this model, we obtain an estimate of the characteristic BLR radius of $50^{+19}_{-23}\,\rm{light \,days}$. This is similar to the estimate of the BLR size obtained by reverberation-mapping analysis $({\sim}100\,\rm{light\, days})$.

scholarly journals 21cm Absorption Lines at High Redshift from Intervening Galaxies

2002 ◽  
Vol 199 ◽  
pp. 83-90 ◽  
Author(s):  
F. H. Briggs
Keyword(s):  
Absorption Line ◽  
High Redshift ◽  
Neutral Hydrogen ◽  
Radio Galaxies ◽  
Hydrogen Gas ◽  
Absorption Lines ◽  
Radio Sources ◽  
Evolution Of Galaxies ◽  
Neutral Gas ◽  
Extended Radio

Radio absorption line observations of neutral hydrogen gas against extended radio sources offers the means to measure sizes and kinematics in intervening galaxies at all redshifts up to the maximum redshift where radio galaxies are detected. Such observations can therefore trace the evolution of galaxies at redshifts z ≳ 2 where the damped Lyman — α statistics indicate that the mass in neutral gas exceeded the mass in stars.

scholarly journals Absorption-Line Spectroscopy of Close Pairs of QSOs

1983 ◽  
Vol 104 ◽  
pp. 369-370
Author(s):  
P. A. Shaver ◽  
J. G. Robertson
Keyword(s):  
Absorption Line ◽  
Cross Sections ◽  
High Redshift ◽  
The Other ◽  
Absorption Lines ◽  
Clusters Of Galaxies ◽  
Absorption Cross ◽  
Powerful Approach ◽  
Metal Absorption ◽  
Close Pairs

Close pairs of QSOs (separations ≲ 1–5 arcmin) provide a powerful approach to the study of narrow absorption lines in QSO spectra. By looking for absorption in the spectrum of the higher-redshift QSO at the redshift of the other (“associated absorption”), or absorption in both spectra at the same redshift (“common absorption”), one may address several issues: the cosmological nature of QSO redshifts, the origin of the narrow absorption lines of high redshift and excitation (intrinsic or intervening), the clustering of absorbing systems (with each other, and with QSOs), the sizes of the absorbing regions (for metal absorption lines and for Lyα lines; absorption cross-sections of individual galaxies and of clusters of galaxies), and the presence and nature of gaseous halos around QSOs.

scholarly journals Reionisation and High-Redshift Galaxies: The View from Quasar Absorption Lines

2015 ◽  
Vol 32 ◽  
Author(s):  
George D. Becker ◽  
James S. Bolton ◽  
Adam Lidz
Keyword(s):  
Intergalactic Medium ◽  
High Redshift ◽  
Absorption Lines ◽  
Metal Line ◽  
Quasar Absorption Lines ◽  
History Of ◽  
Low Mass ◽  
To Come ◽  
First Galaxies ◽  
High Redshift Universe

AbstractDetermining when and how the first galaxies reionised the intergalactic medium promises to shed light on both the nature of the first objects and the cosmic history of baryons. Towards this goal, quasar absorption lines play a unique role by probing the properties of diffuse gas on galactic and intergalactic scales. In this review, we examine the multiple ways in which absorption lines trace the connection between galaxies and the intergalactic medium near the reionisation epoch. We first describe how the Ly α forest is used to determine the intensity of the ionising ultraviolet background and the global ionising emissivity budget. Critically, these measurements reflect the escaping ionising radiation from all galaxies, including those too faint to detect directly. We then discuss insights from metal absorption lines into reionisation-era galaxies and their surroundings. Current observations suggest a buildup of metals in the circumgalactic environments of galaxies over z ~ 6 to 5, although changes in ionisation will also affect the evolution of metal line properties. A substantial fraction of metal absorbers at these redshifts may trace relatively low-mass galaxies. Finally, we review constraints from the Ly α forest and quasar near zones on the timing of reionisation. Along with other probes of the high-redshift Universe, absorption line data are consistent with a relatively late end to reionisation (5.5 ≲ z ≲ 7); however, the constraints are still fairly week. Significant progress is expected to come through improved analysis techniques, increases in the number of known high-redshift quasars from optical and infrared sky surveys, large gains in sensitivity from next-generation observing facilities, and synergies with other probes of the reionisation era.

scholarly journals H2/HD molecular data for analysis of quasar spectra in search of varying constants

2019 ◽  
Vol 622 ◽  
pp. A127 ◽  
Author(s):  
W. Ubachs ◽  
E. J. Salumbides ◽  
M. T. Murphy ◽  
H. Abgrall ◽  
E. Roueff
Keyword(s):  
Vacuum Ultraviolet ◽  
High Redshift ◽  
Sensitivity Coefficient ◽  
Molecular Data ◽  
Oscillator Strengths ◽  
Absorption Lines ◽  
Electron Mass ◽  
Mass Ratio ◽  
Quasar Spectra ◽  
Varying Constants

Context. Absorption lines of H2 and HD molecules observed at high redshift in the line of sight towards quasars are a test ground to search for variation of the proton-to-electron mass ratio μ. For this purpose, results from astronomical observations are compared with a compilation of molecular data of the highest accuracy, obtained in laboratory studies as well as in first-principles calculations. Aims. A comprehensive line list is compiled for H2 and HD absorption lines in the Lyman (B1Σu+ − X1Σg+) and Werner (C1Πu − X1Σg+) band systems up to the Lyman cutoff at 912 Å. Molecular parameters listed for each line i are the transition wavelength λi, the line oscillator strength fi, the radiative damping parameter of the excited state Γi, and the sensitivity coefficient Ki for a variation of the proton-to-electron mass ratio. Methods. The transition wavelengths λi for the H2 and HD molecules are determined by a variety of advanced high-precision spectroscopic experiments involving narrowband vacuum ultraviolet lasers, Fourier-transform spectrometers, and synchrotron radiation sources. Results for the line oscillator strengths fi, damping parameters Γi, and sensitivity coefficients Ki are obtained in theoretical quantum chemical calculations. Results. A new list of molecular data is compiled for future analyses of cold clouds of hydrogen absorbers, specifically for studies of μ-variation from quasar data. The list is applied in a refit of quasar absorption spectra of B0642–5038 and J1237+0647 yielding constraints on a variation of the proton-to-electron mass ratio Δμ/μ consistent with previous analyses.

scholarly journals CAN UVB VARIATIONS RECONCILE SIMULATED QUASAR ABSORPTION LINES AT HIGH REDSHIFT?

2020 ◽  
Vol 56 (1) ◽  
pp. 97-107
Author(s):  
L. A. Garcı́a ◽  
E. V. Ryan-Weber
Keyword(s):  
Metal Ions ◽  
High Redshift ◽  
Statistical Properties ◽  
Absorption Lines ◽  
Quasar Absorption Lines ◽  
Synthetic Metal ◽  
Absorption Features

In this work we present new calculations of the observables associated with synthetic metal and HI absorption lines in the spectra of high redshift quasars, in-spired by questions and limitations raised in work with a uniform Haardt-Madau 2012 ultraviolet background (UVB). We introduce variations at z ≈ 6 to the UVB and HI self–shielding and explore the sensitivity of the absorption features to modifications of the hardness of the UVB. We find that observed SiIV and low ionization states (e.g. CII, SiII, OI) are well represented by a soft UV ionizing field at z = 6, but this same prescription, fails to reproduce the statistical properties of the observed CIV ion absorber population. We conclude that small variations in the UVB (not greater than a dex below Haardt-Madau 2012 emissivity at 1 Ryd) and HI SSh at z ≈ 6 play a major role in improving the estimation of metal ions and HI statistics at high z.

NARROW QUASAR ABSORPTION LINES AND THE HISTORY OF THE UNIVERSE

1994 ◽  
Vol 03 (04) ◽  
pp. 723-729 ◽  
Author(s):  
DIERCK-EKKEHARD LIEBSCHER
Keyword(s):  
Cosmological Model ◽  
Column Density ◽  
Absorption Lines ◽  
Quasar Absorption Lines ◽  
Quasar Spectra ◽  
Size Number ◽  
Wide Range ◽  
History Of ◽  
The Universe ◽  
Fast Evolution

In order to get an estimation of the parameters of the cosmological model the statistics of narrow absorption lines in quasar spectra is evaluated. To this end a phenomenological model of the evolution of the corresponding absorbers in density, size, number and dimension is presented and compared with the observed evolution in the spectral density of the lines and their column density seen in the equivalent width. In spite of the wide range of possible models, the Einstein-deSitter model is shown to be unlikely because of the implied fast evolution in mass.

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