A Spectroscopic Study of UM 673 A and B: On the Size of Lyman-Alpha Clouds
Abstract
We present a study of the Lyα forest spectra (2 A resolution) obtained for the A and B images of the gravitationally lensed high- redshift quasar UM 673. We also present higher resolution data of the brightest (A) image. In the 2 A resolution spectra, all the absorption lines detected at 5 σ in the spectrum of the fainter B image are present in the A image; however, we find two anticoincidences, i.e., two lines in A which do not have a counterpart in B at more than a 3 σ confidence level. Given the fact that corresponding Lyα lines in the spectra of A and B have their equivalent widths well correlated, this proves that both light beams actually cross the same clouds. Most of the velocity differences between corresponding lines are compatible with 0 km s^-1^ within the error bars, with a standard deviation of 17 km s^-1^. As the comoving linear separation increases from virtually 0h^-1^_50_ kpc (H_0_ = 50h_50_ km s^-1^ Mpc^-1^, q_0_ = 0) at the redshift of the QSO to 2h^-1^_50_ kpc, we derive a best value of 12h^-1^_50_1 kpc for the 2 σ lower limit and of 160h^-1^_50_ kpc for the 2 σ upper limit of the diameter of spherical Lyα clouds in the redshift range 2.1-2.7, by means of Monte Carlo simulations. However, if we interpret the two anticoincidences as due to a Mg II doublet at z = 0.4261, we find in this case a best value of 23h^-1^_50_ kpc to the 2 σ lower limit of the Lyα cloud diameter, but we cannot derive any upper limit. For the two major heavy-element systems detected in the spectrum of UM 673, we do not find any significant difference between the corresponding lines in the two spectra, indicating that these systems do not show dramatic variations over scales of 0.8h^-1^_50_ and 2.1h^-1^_50_ kpc, respectively.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1992
- DOI:
- 10.1086/171187
- Bibcode:
- 1992ApJ...389...39S
- Keywords:
-
- Astronomical Spectroscopy;
- Galactic Mass;
- Gravitational Lenses;
- Lyman Alpha Radiation;
- Quasars;
- Red Shift;
- Absorption Spectra;
- Heavy Elements;
- Hubble Constant;
- Line Spectra;
- Monte Carlo Method;
- Astrophysics;
- COSMOLOGY: GRAVITATIONAL LENSING;
- GALAXIES: QUASARS: ABSORPTION LINES;
- GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: UM 673