Analysis of Lyalpha absorption lines in the vicinity of QSOs
Abstract
We have compiled, from the literature, a sample of Lyalpha forest lines in the spectra of 69 quasi-stellar objects (QSOs), all observed with a resolution of between 60 and 100 km s^-1. The sample is studied for the proximity effect. We have tried to account for the effect of blending which is inherent in the intermediate resolution sample by calculating the column density distribution, using an effective velocity dispersion parameter, from the observed equivalent width distribution. The use of this column density distribution in the proximity effect analysis reduces the background intensity values by a factor of 2 to 3 compared with the values obtained by using the column density distribution obtained from high-resolution observations. Evidence is presented for a weak correlation between the effective velocity dispersion parameter and equivalent width. Such a correlation, if present, can increase the background values by a factor of up to 1.5. Considerations of proximity in the spectra of 16 QSOs from our sample, exhibiting damped Lyalpha lines, give a background intensity that is three times smaller than the values obtained from the whole sample, confirming the presence of dust in the damped Lyalpha systems. Lines close to the QSOs are shown to be marginally stronger and broader compared with lines away from the QSOs. The Lyalpha lines with an absorption redshift larger than the emission redshift are shown to be uncorrelated with QSO luminosity, radio loudness or optical spectral index. These lines occur more frequently at high redshifts. Their presence is correlated weakly with the presence of associated metal line systems. The possibilities that the QSO emission redshift is considerably higher and that either the Lyalpha clouds or the QSOs have peculiar velocities are considered. It is argued that a combination of both of these phenomena may be required to account for the presence of these lines.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 1996
- DOI:
- 10.1093/mnras/280.3.767
- arXiv:
- arXiv:astro-ph/9511048
- Bibcode:
- 1996MNRAS.280..767S
- Keywords:
-
- QUASARS: ABSORPTION LINES;
- Astrophysics
- E-Print:
- 33 pages, revtex, 8 figures available on request at anand@iucaa.ernet.in. (MNRAS in press)