Lyman Edge Research Articles

Detection of Lyman continuum absorption in the BL Lacertae object PKS 0735+178

view Abstract Citations (15) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Lyman continuum absorption in the BL Lacertae object PKS0735+178. Bregman, J. N. ; Glassgold, A. E. ; Huggins, P. J. Abstract The detection of the Lyman edge in the BL Lac object PKS 0735+178 at the absorption red shift determined by optical measurements leads to a lower limit for the column density of atomic hydrogen, N(H I) not less than 4(17)/sq cm. The Lyman-alpha absorption line appears to have been detected, but only an approximate upper limit can be obtained from the data, of the order of 2(19)/sq cm. This amount of atomic hydrogen is less than that for a line of sight through the disk of a normal spiral galaxy. It is suggested that the absorbing material exists either in the halo of a galaxy or in the tenuous, extended, gaseous disk of a galaxy. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159253 Bibcode: 1981ApJ...249...13B Keywords: Bl Lacertae Objects; Lyman Spectra; Quasars; Ultraviolet Absorption; Absorption Spectra; Gas Density; Hydrogen Atoms; Iue; Red Shift; Astronomy full text sources ADS | data products SIMBAD (1) NED (1) MAST (1)

IUE Observations of Quasars

Spectra of six quasars have been obtained with the International Ultraviolet Explorer Satellite. Five of the six show no evidence for strong Lyα absorption between the redshifted and rest wavelengths, for .23≤ zem ≤1.72. In addition, the quasar PG 1115+080 at z=1.72 shows no evidence for strong He I absorption from the resonance transition at λ584 Å. These results confirm that the intergalactic medium must be both tenuous and hot enough to produce an optical depth <0.1 in neutral hydrogen and helium. In no case was the Lyman edge detected in absorption near zem. Four of the objects produce an average Lyα/Hβ intensity ratio of 6.3, in disagreement with the theoretical prediction for Case B optically thick recombination of 30. Also, two of the objects show Lyγ in emission, a result unexpected from Case B line transfer assumptions. The Lyα emission line in 3C 351 shows the identical sharp core plus 20,000 km s−1 broad wings observed in Hβ and Mg II, implying a common origin in the same dynamical ensemble of emitting regions. These quasars show systematically steeper spectral indices when the energy distributions are fit from the ultraviolet through the visible than those derived from the visible spectra alone. PG 1115+080 shows a featureless continuum down to an observed λ1173 Å. The ionizing spectrum, with fν αν−2.0, therefore persists beyond 2 Rydbergs. The spectrum of PG 1247+268, with z=2.038, contains a strong absorption line at observed λ2697 Å, with no net flux detected from λ2000 Å down to the observed limit at λ1150 Å. This result is interpreted as absorption in Lyα and the Ly edge at z=1.218. Low dispersion optical spectra show no evidence for Mg II or C IV absorption in the same system; the signal to noise ratio is too low in the IUE spectrum to confirm Lyβ. We conclude that the line of sight intersects a metal-poor cloud with τ ≲ 1 in the Ly continuum, at (1+zem)/(1 + zabs) = 1.37.

Radiative shock dynamics. I - The Lyman continuum

view Abstract Citations (35) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative shock dynamics. I. The Lyman continuum. Klein, R. I. ; Stein, R. F. ; Kalkofen, W. Abstract The paper investigates coupled non-LTE radiative transfer and nonlinear hydrodynamics by considering a shock propagating outward through an atmosphere of pure hydrogen in which the hydrogen atoms have one bound level and a continuum. Self-consistent numerical solutions are obtained for the nonlinear hydrodynamic equations, the transfer equation for Lyman continuum radiation, and the time-dependent population equation for atoms with one bound level plus continuum. Results are discussed for a piston-driven shock propagating through a static atmosphere in radiative and statistical equilibrium, with attention given to the formation of the ionization front, the ionization contour, and the radiation intensity at the Lyman edge. The structure of the temperature spike developed by the shock is compared for the three cases of adiabatic, collisional, and radiating shocks. It is shown that the escape of recombination radiation narrows the temperature spike at small optical depth and that low postshock densities in the upper atmosphere reduce the three-body recombination rate and produce a large plateau of nearly constant ionization behind the shock. Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154304 Bibcode: 1976ApJ...205..499K Keywords: Hydrodynamics; Hydrogen Atoms; Lyman Spectra; Radiative Transfer; Shock Wave Propagation; Stellar Atmospheres; Atmospheric Models; Continuous Radiation; Finite Difference Theory; Gas Ionization; Hydrodynamic Equations; Temperature Profiles; Thermodynamic Equilibrium; Astrophysics full text sources ADS |