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2008ApJ...679..194D - Astrophys. J., 679, 194-219 (2008/May-3)

The low-z intergalactic medium. III. H I and metal absorbers at z < 0.4.

DANFORTH C.W. and SHULL J.M.

Abstract (from CDS):

We conduct an ultraviolet (HST and FUSE) spectroscopic survey of H I (Lyman lines) and seven metal ions (O VI, N V, C IV, C III, Si IV, Si III, Fe III) in the low-redshift IGM at z<0.4. We analyzed 650 Lyα absorbers over redshift path length Δz=5.27, detecting numerous absorbers: 83 O VI systems, 39 C III, 53 Si III, 24 C IV, 24 N V, and so on. In the low-z IGM, we have accounted for ∼40% of the baryons: 30% in the photoionized Lyα forest and 10% in the (T=105-106) WHIM traced by O VI. Statistical metallicities are consistent with the canonical value of 10% solar, with considerable scatter. Improved statistics for weak absorbers allows us to estimate ΩWHIMb=0.073±0.008 down to logN_OVI_=13.4 and 0.086±0.008 down to logN_OVI_=13.0. The O VI absorber line frequency, dN/dz=40+14–8, down to 10 mÅ equivalent width suggests a 250-300 kpc extent of metals around dwarf galaxies. Many absorbers appear to contain multiphase gas, with both collisional ionization and photoionization determining the ionization state. N V absorption is well correlated with O VI, and both ions show similarly steep power-law indices dN/dz∝N–β with β_OVINV_~2 while β_HI_=1.7. We conclude that O VI and N V are reliable tracers of the portion of the WHIM at T~105-106 K. C IV may be present in both collisional and photoionized phases; N_CIV_ correlates poorly with both N_HI_ and N_OVI_and β_HICIVOVI_. The ions C III, Si III, and Si IV are well correlated with H I and show patterns typical of photoionization. Adjacent ion stages of the same element (C III/IV and Si III/IV) provide useful constraints on the photoionization parameter, logU~-1.5±0.5.

Abstract Copyright:

Journal keyword(s): Cosmology: Cosmological Parameters - Cosmology: Observations - Galaxies: Intergalactic Medium - Galaxies: Quasars: Absorption Lines - Ultraviolet: General

VizieR on-line data: <Available at CDS (J/ApJ/679/194): table1.dat table2.dat table4.dat>

Nomenclature: Tables 2, 4: [DS2008] QSO JHHMM+DDMM abs N.NNNNN N=650.

CDS comments: In tables HE 0226-4410 is a misprint for HE 0226-4110

Simbad objects: 37

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