First comparison of ionization and metallicity in two lines of sight toward HE 1104-1805 AB at z=1.66

S Lopez*, D Reimers, M Rauch, WLW Sargent, A Smette

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

72 Citations (Scopus)

Abstract

Using new Nubble Space Telescope Faint Object Spectrograph, the New Technology Telescope ESO Multi Mode Instrument, and Keck HIRES spectra of the gravitationally lensed double QSO HE 1104-1805 AB (z(em) = 2.31) and assuming UV photoionization by a metagalactic radiation held, we derive physical conditions (ionization levels, metal abundances, and cloud sizes along the lines of sight) in five C IV + Mg II absorption systems clustered around z = 1.66 along the two lines of sight. Three of these systems are associated with a damped Ly alpha (DLA) system with log N(N I)= 20.85, which is observed in the UV spectra of the bright QSO image, A. The other two systems are associated with a Lyman-limit system with log N(H I)= 17.57 seen in the fainter image, B. The Cry and Mg II line profiles in A resemble those in the B spectra and span Delta v approximate to 360 km s(-1). The angular separation, theta = 3.195 ", between A and B corresponds to a transverse proper separation of S-perpendicular to = 8.3 h(50)(-1) kpc for q(0) = 0.5 and a lens at z = 1. Assuming that the relative metal abundances in these absorption systems are the same as those observed in the DLA system, we find that the observed N(C IV)/N(Mg II) ratios imply ionization parameters of log Gamma = -2.95 to - 2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density of n(H) less than or similar to 0.01 cm(-3)) and relatively highly ionized. The absorption systems to B are found to have a metallicity 0.63 times lower than the metallicity of the gas giving rise to the DLA system, Z(DLA) similar or equal to 1/10 Z(circle dot). We detect O vr at z = 1.66253 in both QSO spectra but no associated N v. Our model calculations lead us to conclude that the C Iv clouds should be surrounded by large (similar to 100 kpc), highly ionized low-density clouds (n(H) similar to 10(-4) cm(-3)) in which O vr, but only weak C IV, absorption occurs. In this state, log Gamma greater than or equal to -1.2 reproduces the observed ratio of N(O vr)/N(N v)> 60. These results are discussed in view of the disk/halo and hierarchical structure formation models.

Original languageEnglish
Pages (from-to)598-618
Number of pages21
JournalAstrophysical Journal
Volume513
Issue number2
Publication statusPublished - 10-Mar-1999

Keywords

  • galaxies : abundances
  • gravitational lensing
  • quasars : absorption lines
  • quasars : individual (HE 1104-1805 AB)
  • O-VI ABSORPTION
  • DOUBLE QSO HE-1104-1805
  • GAS-PHASE ABUNDANCES
  • LY-ALPHA SYSTEMS
  • HIGH-REDSHIFT
  • GRAVITATIONAL LENS
  • GALAXY
  • QUASAR
  • SIZE
  • DUST

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