The Absorption Spectrum of Nuclear Gas in Q0059-2735
Abstract
Spectra of the broad absorption line (BAL) quasar Q0059 -2735 taken with spectral resolutions of 10 and 20 km s^-1^ show that the absorption lines can be understood as a BAL flow together with low-ionization condensations. The condensations produce narrow (b <~ 20 km s^-1^), saturated lines that fail to occult completely the central continuum sources or the low-ionization emission-line sources. Many of the narrow absorption lines (NAL) originate from metastable levels that lie several electron volts above the ground term. The level populations imply excitation temperatures of ~10^4^ K. These levels may be populated either by collisional or radiative processes. Models show that the NAL gas lies a few parsecs from the central source. The BAL absorption is much deeper than the NAL absorption. The high- ionization BAL flow must occult most of the quasar nucleus, but the shapes of the low-ionization BAL absorption troughs show that while the low-ionization BAL gas occults the nuclear continuum sources it fails to occult the low-ionization broad emission line region. Compared to the NAL clouds, the BAL clouds have a higher excitation temperature, ranging up to 6 x 10^4^ K. All these observed facts can be explained by a model in which low- ionization gas condensations lying above an accretion disk are being ablated by the intense radiation field of the quasar nucleus. The low- ionization condensations and the BAL flow occult different parts of the background emission regions. The origin of the low-ionization clouds is uncertain: they could be ablating stellar atmospheres, as suggested by Baldwin et al. (1993), or stand-off shocks around obstacles in a hot, supersonic flow of low-density gas from the central QSO nucleus (Perry & Dyson 1985), or they could be dense gas clouds, ejected by a supernova explosion (Artymowicz, Lin, & Wampler 1993) or, possibly, by instabilities in the accretion disk.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1995
- DOI:
- 10.1086/175551
- Bibcode:
- 1995ApJ...443..586W
- Keywords:
-
- Absorption Spectra;
- Accretion Disks;
- Astronomical Models;
- Atomic Energy Levels;
- Computer Programs;
- Continuous Spectra;
- Interstellar Gas;
- Quasars;
- Gas Flow;
- Gas Ionization;
- Metastable State;
- Occultation;
- Shock Waves;
- Spectrographs;
- Stellar Atmospheres;
- Astrophysics;
- GALAXIES: QUASARS: ABSORPTION LINES;
- GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: Q0059-;
- 735