SIMBAD references

2003ApJ...587..551D - Astrophys. J., 587, 551-561 (2003/April-3)

A quadruple-phase strong mg II absorber at z ∼ 0.9902 toward PG 1634+706(1,).

DING J., CHARLTON J.C., BOND N.A., ZONAK S.G. and CHURCHILL C.W.

Abstract (from CDS):

The z=0.9902 system along the quasar PG 1634+706 line of sight is a strong Mg II absorber [W_r(λ2796)>0.3 Å] with only weak C IV absorption (it is ``C IV-deficient''). To study this system, we used high-resolution spectra from both the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) and the Keck I telescope High Resolution Echelle Spectrometer (HIRES). The STIS spectrum has a resolution of R=30,000 and covers key transitions such as Si II, C II, Si III, C III, Si IV, and C IV. The HIRES spectrum, with a resolution of R=45,000, covers the Mg I, Mg II, and Fe II transitions. Assuming a Haardt & Madau extragalactic background spectrum, we modeled the system with a combination of photoionization and collisional ionization. Based on a comparison of synthetic spectra with the data profiles, we infer the existence of the following four phases of gas:

(1.)
Seven Mg II clouds have sizes of 1-1000 pc and densities of 0.002-0.1 cm^–3, with a gradual decrease in density from blue to red. The Mg II phase gives rise to most of the C IV absorption and resembles the warm, ionized intercloud medium of the Milky Way.
(2.)
Instead of arising in the same phase as Mg II, Mg I is produced in separate, narrow components with b∼0.75 km/s. These small Mg I pockets (∼100 AU) could represent a denser phase (∼200 cm^–3) of the interstellar medium (ISM), analogous to the small-scale structure observed in the Milky Way ISM.
(3.)
A ``broad phase'' with a Doppler parameter b∼60 km/s is required to consistently fit Lyα, Lyβ, and the higher order Lyman series lines. A low metallicity (logZ≲-2) for this phase could explain why the system is ``C IV-deficient'' and also why N V and O VI are not detected. This phase may be a galactic halo, or it could represent a diffuse medium in an early-type galaxy.
(4.)
The strong absorption in Si IV relative to C IV could be produced in an extra, collisionally ionized phase with a temperature of T∼60,000 K. The collisional phase could exist in cooling layers that are shock heated by supernova-related processes.

Abstract Copyright: ∼

Journal keyword(s): Galaxies: Evolution - Galaxies: Halos - Galaxies: Quasars: Absorption Lines

Simbad objects: 5

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