[Previous] | [Session 18] | [Next]
N. Arav (UC, Davis), M. de Kool (Astrophysical Theory Centre, ANU, Australia), R. H. Becker, S. A. Laurent-Muehleisen (UC, Davis; and IGPP, LLNL), R. L. White (STScI), T. Price, M. D. Gregg (UC, Davis; and IGPP, LLNL)
This paper presents an analysis of a Keck HIRES spectrum of the BALQSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 Å. The line of sight towards the QSO contains two clusters of outflowing clouds giving rise to broad absorption lines. Their velocities range from -200 to -1200 km/s and from -3400 to -5200 km/s respectively. The most prominent absorption lines are those of Mg II, Mg I and Fe II. Mn II is also present.
Absorption from excited states of Fe II is clearly detected, and allows a determination of the population of several low lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE. This constrains the electron density in the line forming regions, ne<104 cm-3. If this low density absorbing matter is exposed to a normal QSO ionizing continuum, the observed column densities of Mg I and Fe II and the absence of Fe I absorption constrain the ionization parameter of the clouds to lie in the range 10-5 < U < 10-3. For a typical QSO luminosity of 1046 erg/s, this implies a distance between 0.3 and 3 kiloparsec from the continuum source, i.e. typical of the narrow line region. The observed Fe II column density indicates that the clouds are between 1014 and 1015 cm thick, and geometrically bounded.