The absorption spectrum of nuclear gas in Q0059-2735

Details The absorption spectrum of nuclear gas in Q0059-2735 The absorption spectrum of nuclear gas in Q0059-2735

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..586w&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 2, p. 586-605

Astronomy and Astrophysics

Astrophysics

67

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

Scientific paper

Spectra of the broad absorption line (BAL) quasar Q0059-2735 taken with spectral resolutions of 10 and 20 km/s show that the absorption lines can be understood as a BAL flow together with low-ionization condensations. The condensations produce narrow (b less than or approximately equal to 20 km/s), 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 approximately 104 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 104 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.

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