Spectra Of Quasi-stellar Objects Research Articles

Physical conditions in quasi-stellar object absorbers from fine-structure absorption lines

We calculate theoretical population ratios of the ground fine-structure levels of some atoms/ions which typically exhibit ultraviolet (UV) lines in the spectra of quasi-stellar objects (QSO) absorbers redward the Lyα forest: C0, C+, O0, Si+ and Fe+. The most reliable atomic data available are employed and a variety of excitation mechanisms are considered: collisions with several particles in the medium, direct excitation by photons from the cosmic microwave background radiation (CMBR) and fluorescence induced by a UV field present. The theoretical population ratios are compared with the corresponding column density ratios of Ci and Cii lines observed in damped Lyα (DLA) and Lyman Limit (LL) systems, collected in the recent literature, to infer their physical conditions. The volumetric density of neutral hydrogen in DLA systems is constrained to be lower than tens of cm−3 (or a few cm−3 in the best cases), and upper limits to the UV radiation field intensities to be about two orders of magnitude bigger than the radiation field of the Galaxy (one order of magnitude in the best cases). Their characteristic sizes are higher than a few pc (tens of pc in the best cases) and lower limits for their total masses vary from 100 to 105 solar masses. For the only LL system in our sample, the electronic density is constrained to be . We suggest that the fine-structure lines may be used to discriminate between the current accepted picture of the UV extragalactic background as the source of ionization in these systems and a local origin for the ionizing radiation as supported by some authors. We also investigate the validity of the temperature–redshift relation of the CMBR predicted by the standard model and study the case for alternative models.

A Uniform Analysis of the Lyα Forest at z = 0–5. II. Measuring the Mean Intensity of the Extragalactic Ionizing Background Using the Proximity Effect

Moderate-resolution data for 40 quasi-stellar objects (QSOs) at z ≈ 2 were combined with spectra of comparable resolution of 59 QSOs with redshifts greater than 1.7 found in the literature to form a large, homogeneous sample of moderate-resolution (~1 A) QSO spectra. These spectra were presented and the statistics of the Lyα forest were discussed in Paper I. In this analysis, we demonstrate that a proximity effect is present in the data; i.e., there exists a significant (5.5 σ) deficit of lines at zabs ≈ zem. Within 1.5 h-1 Mpc of the QSO emission redshift, the significance does depend on QSO luminosity, in accordance with the theory that this effect is caused by enhanced ionization of hydrogen in the vicinity of the QSO from UV photons from the QSO itself. The photoionization model of Bajtlik, Duncan, & Ostriker permits an estimate of the mean intensity of the extragalactic background radiation at the Lyman limit. We compare the results of this standard analysis with those obtained using a maximum likelihood technique. If the spectrum of the background is assumed to be identical to that of each individual QSO, and if this background is assumed to be constant over the redshift range 1.7 < z < 3.8, then the best-fit value for J(ν0) is found to be 1.4 × 10-21 ergs s-1 cm-2 Hz-1 sr-1, using QSO redshifts based on the Lyα emission line. Systemic QSO redshifts based on the [O III] λ5007 emission line for 19 objects in our sample show an average redshift of ~400 km s-1 with respect to Lyα emission. Using redshifts based on [O III] or Mg II for the 35 objects for which they are measured and adding 400 km s-1 to the remaining QSO Lyα redshifts gives a lower value of J(ν0), 7.0 × 10-22 ergs s-1 cm-2 Hz-1 sr-1. This value is in reasonable agreement with the predictions of various models of the ionizing background based on the integrated quasar luminosity function. Allowing for the fact that individual QSOs have different spectral indices that may also be different from that of the background, we use the standard methods to solve for the H I photoionization rate, Γ, and the parameters describing its evolution with redshift. The best-fit value for the H I ionization rate we derive is 1.9 × 10-12 s-1, in good agreement with models of the background that incorporate QSOs only. Finally, we use simulated Lyα forest spectra including the proximity effect to investigate curve-of-growth effects in the photoionization model used in the analysis. We find that the presence of lines on the saturated part of the curve of growth could cause our estimates of the background intensity to be overestimated by a factor of 2-3. This large absorption-line sample and these techniques for measuring the background and understanding the systematics involved allow us to place what we believe are the firmest limits on the background at these redshifts.

Broadening of spectral lines due to dynamic multiple scattering and the Tully-Fisher relation

The frequency shift of spectral lines is most often explained by the Doppler effect in terms of relative motion, whereas the Doppler broadening of a particular line mainly depends on the absolute temperature. The Wolf effect, on the other hand, deals with the correlation-induced spectral change and explains both the broadening and shift of the spectral lines. In this framework a relation between the width of the spectral line is related to the redshift z for the line and hence with the distance. For smaller values of z a relation similar to the Tully-Fisher relation can be obtained and for larger values of z a more general relation can be constructed. The derivation of this kind of relation based on dynamic multiple-scattering theory may play a significant role in explaining the overall spectra of quasistellar objects. We emphasize that this mechanism is not applicable for nearby galaxies, $z&lt;~1$.

THE LYMAN ALPHA FOREST IN THE SPECTRA OF QUASISTELLAR OBJECTS

▪ Abstract Observations of redshifted Lyman α (Lyα) forest absorption in the spectra of quasistellar objects (QSOs) provide a highly sensitive probe of the distribution of gaseous matter in the universe. Over the past two decades, optical spectroscopy with large ground-based telescopes, and more recently ultraviolet (UV) spectroscopy from space, have yielded a wealth of information on what appears to be a gaseous, photoionized intergalactic medium (IGM), partly enriched by the products of stellar nucleosynthesis, residing in coherent structures over many hundreds of kiloparsecs. Recent progress with cosmological hydro-simulations based on hierarchical structure formation models has led to important insights into the physical structures giving rise to the forest. If these ideas are correct, a truly inter- and protogalactic medium [at high redshift (z ∼ 3), the main repository of baryons] collapses under the influence of dark matter gravity into flattened or filamentary structures, which are seen in absorption against background QSOs. With decreasing redshift, galaxies forming in the denser regions may contribute an increasing part of the Lyα absorption cross section. Comparisons between large data samples from the new generation of telescopes and artificial Lyα forest spectra from cosmological simulations promise to become a useful cosmological tool.

A Catalog of Absorption in the Spectra of Quasi-stellar Objects: Erratum (Orig. paper in 77, 203, 47-B1 (1991))

view Abstract Citations (4) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Catalog of Absorption in the Spectra of Quasi-stellar Objects: Erratum (Orig. paper in 77, 203, 47-B1 (1991)) Junkkarinen, V. ; Hewitt, A. ; Burbidge, G. Abstract In the paper entitled "A Catalog of Absorption in the Spectra of Quasi- stellar Objects" by V. Junkkarinen, A. Hewitt, & G. Burbidge (ApJS, 77,203(1991]) there is an error in Table l. Because of an error in the computer program used to generate the final version of Table 1, the J2000 coordinates for all the objects are incorrect. The error involves the printed values for the J2000 seconds of time in right ascension and the J2000 seconds of arc in declination. The following table gives corrected J2000 coordinates for all the objects in Table 1 of our paper. Table 1 should be consulted for the 1950 coordinates and to check for coordinates which are poorly known. The J2000 coordinate names in Table 1 are correct (except that a few may change as more accurate coordinates become available for those QSOs with poorly determined coordinates), and the B1950 coordinates and coordinate names are not affected by the programming error. Additional corrections: In Table 3, 1040+015 should be QNB1:49, not QNB1:22. Two references were omitted (the numbers appear in Table 1, but the references are not listed): 1720. Djorgovski, S., Strauss, M. A., Perley, R. A., Spinrad, H., and McCarthy, P. 1987, AJ, 93,1318. 2115. Turnshek, D. A., Wolfe, A. M., Lanzetta, K. M., Briggs, F. H., Cohen, R. D., Foltz, C. B., Smith, H. E., and Wilkes, B. J. 1989, ApJ, 344,567. We would like to thank Marion Schmitz (IPAC) for pointing out the missing references and QNB1:49. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1992 DOI: 10.1086/191699 Bibcode: 1992ApJS...81..409J Keywords: ERRATA; ADDENDA full text sources ADS | Related Materials (1) Original Paper: 1991ApJS...77..203J

A catalog of absorption in the spectra of quasi-stellar objects

view Abstract Citations (63) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Catalog of Absorption in the Spectra of Quasi-stellar Objects Junkkarinen, V. ; Hewitt, A. ; Burbidge, G. Abstract This paper contains a compilation of basic information on QSO absorption systems. A total of 724 QSOs are listed in three tables. Table 1 contains 353 QSOs that have absorption-line systems with measured redshifts. The numerous Lyα forest systems based only on narrow hydrogen lines are excluded from Table 1. Absorption systems with multiple components are listed only once if all of the components fall within a span of 500 km s^-1^. A total of 862 systems with narrow metal lines which we consider to be reliably identified are listed in Table 1. Table 1 contains an additional 260 systems consisting of less certain systems, damped Lyα systems, and Lyman limit systems that have no detected narrow metal lines. In Table 2 we list 146 broad absorption line QSOs. Fifteen of these have narrow absorption line systems identified, and thus they also appear in Table 1. In Table 3 we give an inhomogeneous list of 240 QSOs in which absorption systems have been seen but not measured. Also shown are histograms of emission redshift, absorption redshift, and (1 + Z_em_)/( 1 + Z_abs_) for the reliably identified narrow metal line systems. Several selection effects are apparent in this collection of data. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1991 DOI: 10.1086/191602 Bibcode: 1991ApJS...77..203J Keywords: Absorption Spectra; Astronomical Catalogs; Astronomical Spectroscopy; Quasars; Emission Spectra; Lyman Alpha Radiation; Red Shift; Astrophysics; GALAXIES: REDSHIFTS; LINE IDENTIFICATIONS; QUASARS full text sources ADS | data products NED (1454) SIMBAD (633) CDS (1) Related Materials (1) Erratum: 1992ApJS...81..409J

An inhomogeneous reference catalogue of identified intervening heavy element systems in spectra of QSOs

Identifications of heavy element line systems, observed in spectra of quasi-stellar objects between 1965 and 1989 inclusive, are collected and tabulated with references. Each system is assigned a quality grade based on the apparent reliability of the data. The highest quality systems are used to characterize the absorbers as a sample. We confirm a decrease in C IV line strength with redshift (z), and the corresponding decrease in line density per unit z with z. The weakest C IV systems, at high z, are accompanied by relatively stronger Si IV lines, compared to the relative line strengths at low z. The space density of systems with strong lines of first ions is nearly independent of z below z = 3, though it drops at z > 3. Preliminary tests for quasar lensing by intervening systems and for clustering of absorbers on large scales are presented.

Absorption lines at Z over 2.3 in spectra of quasi-stellar objects

A magnitude-limited sample of nine QSOs with redshifts z over about 3 was selected to look for intervening absorbers with z about 2.3-3.0. Thirty-five possible systems are found, 22 of which were not previously known. The main purpose was to search for a change in the number of the absorbers with redshift. A simple power law does not fit the data, owing to an excess of absorbers at z = 2 to 2.5. In an equivalent path length Delta z about 1.0 at z approximately 2.4, four intervening absorbers are found, whereas in Delta z about 1 at z about 3.2, no intervening absorbers are found. In addition, a slight lowering of ionization with z is found, and an increase in the relative number of weak C IV systems is found as z increases. 22 refs.

On the identification of absorption lines with small red shifts in the spectra of quasistellar objects

The reliability of identifications of narrow absorption lines with small red shifts is analyzed statistically on the basis of literature data on spectra with high spectral resolution for 38 quasi-stellar objects. The identifications were made using a reference spectrum including the most pronounced lines of the interstellar medium. Particular attention is devoted to the case of quasi-stellar objects in the region + or - 10 deg from the supergalactic equator or coincident in position on the celestial sphere with high-latitude high-velocity hydrogen clouds, and also situated at small angular distances from nearby galaxies. It is shown that in the majority of cases identifications with the line pairs of Ca II and Na I are random.

Neutral hydrogen absorption in the spectra of quasi-stellar objects - A search for absorption due to clusters of galaxies

view Abstract Citations (17) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral hydrogen absorption in the spectra of quasistellar objects: a search for absorption due to clusters of galaxies. Peterson, B. M. Abstract A search for neutral hydrogen absorption in the spectra of 17 QSOs appearing in 16 different Abell clusters of galaxies has been performed to determine whether the low-ionization absorption systems observed in QSO spectra arise in rich clusters of galaxies. Cluster redshifts are derived from optical spectra for the 11 clusters without previously reported redshifts. The radio observations reveal no redshifted 21-cm H I features in any of the QSO spectra, indicating that low-ionization absorption systems rarely, if ever, arise in rich clusters. It is suggested that if the low-ionization systems are not intrinsic to the QSOs, they arise in or near isolated galaxies or small groups. The observations are also used to investigate neutral hydrogen absorption systems in the clusters. The lack of detection is shown to support the previous conclusion that clusters of galaxies are not gravitationally bound by optically thick clouds of neutral hydrogen. Publication: The Astrophysical Journal Pub Date: August 1978 DOI: 10.1086/156307 Bibcode: 1978ApJ...223..740P Keywords: Absorption Spectra; Galactic Clusters; Hydrogen Clouds; Quasars; Radio Sources (Astronomy); Red Shift; H Lines; Hydrogen Atoms; Infrared Radiation; Luminous Intensity; Neutral Particles; Astrophysics; Absorption Lines:Quasars; Clusters of Galaxies:Neutral Hydrogen; Clusters of Galaxies:Quasars; Clusters of Galaxies:Redshifts; Quasars:Redshifts full text sources ADS | data products SIMBAD (63) NED (47)

ABSORPTION IN THE SPECTRA OF QUASI-STELLAR OBJECTS AND BL LACERTAE OBJECTS.

ABSTRACT Observations of absorption in the spectra of 64 QSOs and two BL Lac objects are reviewed. Criteria for selecting the absorption-line objects are discussed along with line identifications, properties of identified absorption systems, the observed absence of variability in the absorption lines, the redshift distribution, line locking, and absorption shortward of the Lyman limit. The possibility of noncosmological redshifts is noted, and two interpretations of the absorption-line data are considered: (1) the 'intrinsic' hypothesis that the absorptions arise in gas associated with the QSOs and (2) the 'intervening' hypothesis that they are produced by intervening galaxies, galactic halos, or intergalactic clouds intersected by the line of sight to a QSO. Direct observational tests for the location of the absorbing hydrogen in several individual objects are described. It is concluded that no conclusive observational evidence exists which is capable of establishing whether the absorption is intrinsic or intervening.

Absorption in the Spectra of Quasi-Stellar Objects

A review of the key discoveries concerning absorption lines in QSOs is given. A number of recent studies bearing on the nature and origin of the absorption are discussed. It is concluded that it is most likely that the bulk of the absorption is intrinsic to the QSOs.

Luminosity Indicators in the Spectra of Quasi-Stellar Objects

Luminosity Indicators in the Spectra of Quasi-Stellar Objects

Interacting galaxies and QSO absorption lines

THE spectra of quasi-stellar objects are observed to have absorption lines with redshifts mostly below the redshift of the emission lines1. The absorbing clouds are thought to be either near the QSO1–5 or at cosmological distances from it6–8. On the first interpretation, the clouds are supposed to be accelerated to high velocities (≲ 0.5c away from the QSO) by radiation pressure. However, the small internal velocity dispersions inferred for the clouds from the absorption line widths (∼ 50 km s−1) pose serious problems to this model9 and we consider here the second interpretation. The interception cross section of intervening galaxies for QSO photons has hitherto been calculated10 on the assumption that the galaxies do not evolve. The data so far available (Fig. 1), although probably contaminated by selection effects1, seem to indicate that the number of absorption redshift systems increases more rapidly as a function of the emission line redshift than can be accounted for without such evolution. The possibility has been considered7,8 that the intervening clouds are collapsing protogalaxies, but we think it likely that most galaxies form11 before z = 5 and, instead, attribute the rapid increase in the number of redshift systems to tidal interaction of galaxies at earlier epochs. Because galaxies were closer together in the past, chance collisions were more frequent and the effects of these interactions were more pronounced.

Possibility of a gravitational effect in the spectra of quasi-stellar objects. III

For pt.II see Indian J. Pure Appl. Phys., no.12, p.451 of 1974. It is shown that quasi-stellar objects are most probably situated at cosmological distances. The large redshifts of these objects cannot be due to surface gravitational effects. The Hoyle-Fowler model perhaps holds a last hope of attributing redshift to gravity. Different cluster solutions have been analysed to formulate a suitable Hoyle-Fowler model. A modified Hoyle-Fowler model may explain the emission spectrum of quasars, but such a model fails to give a satisfactory explanation of absorption spectra. However, a Hoyle-Fowler model at cosmological distance may possibly explain sharpness and depth of absorption lines. The Hoyle-Fowler model which was originally designed to provide a non-cosmological model of quasi-stellar objects provides a more satisfactory result if it is at a cosmological distance.

Possibility of a gravitational effect in the spectra of quasi-stellar objects. II

For pt.II see Indian J. Pure Appl. Phys., no.12, p.451 of 1974. It is shown that quasi-stellar objects are most probably situated at cosmological distances. The large redshifts of these objects cannot be due to surface gravitational effects. The Hoyle-Fowler model perhaps holds a last hope of attributing redshift to gravity. Different cluster solutions have been analysed to formulate a suitable Hoyle-Fowler model. A modified Hoyle-Fowler model may explain the emission spectrum of quasars, but such a model fails to give a satisfactory explanation of absorption spectra. However, a Hoyle-Fowler model at cosmological distance may possibly explain sharpness and depth of absorption lines. The Hoyle-Fowler model which was originally designed to provide a non-cosmological model of quasi-stellar objects provides a more satisfactory result if it is at a cosmological distance.

Possibility of a gravitational effect in the spectra of quasi-stellar objects. I

In quasi-stellar objects the redshifts of spectral lines are generally different in absorption and emission. The possibility that the redshift difference in most cases is gravitational is not ruled out. The effect can be seen in a Fowler-Hoyle type model. There exists the possibility that most (but not all) of lines with zab<zem might be associated with quasistellar objects.

Absorption Lines in the Spectra of Quasi-stellar Objects

Weymann and Wilcox1 have recently claimed that there is no evidence that the true occurrence of absorption lines in quasi-stellar objects (QSOs) is a function of red-shift. Such a conclusion, if true, might be considered as evidence against the screening hypothesis discussed by several authors2–4. We feel, however, that the discussion of the data presented by Weymann and Wilcox does not warrant their strongly worded conclusion, and in fact that the data available indicate that the presence of C IV in absorption can be explained by the screening hypothesis.

Concerning Redshifts in the Spectra of Quasi-Stellar Objects

Concerning Redshifts in the Spectra of Quasi-Stellar Objects