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2006ApJ...640..716D - Astrophys. J., 640, 716-740 (2006/April-1)

The low-z intergalactic medium. II. Lyβ, O VI, and C III forest.


Abstract (from CDS):

We present the results of a large survey of H I, O VI, and C III absorption lines in the low-redshift (z<0.3) intergalactic medium (IGM). We begin with 171 strong Lyα absorption lines (Wλ≥80 mÅ) in 31 AGN sight lines studied with the Hubble Space Telescope and measure corresponding absorption from higher order Lyman lines with FUSE. Higher order Lyman lines are used to determine N_HI_and b_HI_accurately through a curve-of-growth (COG) analysis. We find that the number of H I absorbers per column density bin is a power-law distribution, dN/dN_HI∝N-β^_HI_, with β_HI_=1.68±0.11. We made 40 detections of O VI λλ1032, 1038 and 30 detections of C III λ977 out of 129 and 148 potential absorbers, respectively. The column density distribution of C III absorbers has β_CIII_=1.68±0.04, similar to β_HI_but not as steep as β_OVI_=2.2±0.1. From the absorption-line frequency, dN_CIII/dz=12+3^–2for Wλ(C III)>30 mÅ, we calculate a typical IGM absorber size r0∼400 kpc, similar to scales derived by other means. The COG-derived b-values show that H I samples material with T<105 K, incompatible with a hot IGM phase. By calculating a grid of CLOUDY models of IGM absorbers with a range of collisional and photoionization parameters, we find it difficult to simultaneously account for the O VI and C III observations with a single phase. Instead, the observations require a multiphase IGM in which H I and C III arise in photoionized regions, while O VI is produced primarily through shocks. From the multiphase ratio N_HI/NCIII_, we infer the IGM metallicity to be ZC=0.12 Z, similar to our previous estimate of ZO=0.09 Zfrom O VI.

Abstract Copyright:

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

Nomenclature: Table 2: [DSR2006] QSO JHHMM+DDMM abs N.NNNNN N=171.

CDS comments: LBQS 1343+264 A/B = QSO B1343+2640A, QSO B1343+2640B

Simbad objects: 35

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