Super-Solar Metallicity in Weak Mg II Absorption Systems at z ~ 1.7

Abstract

Through photoionization modeling, constraints on the physical conditions of three z ~ 1.7 single-cloud weak Mg II systems (W_r(2796) < 0.3A) are derived. Constraints are provided by high resolution R = 45,000, high signal-to-noise spectra of the three quasars HE0141-3932, HE0429-4091, and HE2243-6031 which we have obtained from the ESO archive of VLT/UVES. Results are as follows: (1) The single-cloud weak Mg II absorption in the three z ~ 1.7 systems is produced by clouds with ionization parameters of -3.8 < logU < -2.0 and sizes of 1-100 pc. (2) In addition to the low-ionization phase Mg II clouds, all systems need an additional 1-3 high-ionization phase C IV clouds within 100 km/s of the Mg II component. The ionization parameters of the C IV phases range from -1.9 < logU < -1.0, with sizes of tens of parsecs to kiloparsecs. (3) Two of the three single-cloud weak Mg II absorbers have near-solar or super-solar metallicities, if we assume a solar abundance pattern. Although such large metallicities have been found for z < 1 weak Mg II absorbers, these are the first high metallicities derived for such systems at higher redshifts. (4) Two of the three weak Mg II systems also need additional low-metallicity, broad Lya absorption lines, offset in velocity from the metal-line absorption, in order to reproduce the full Lya profile. (5) Metallicity in single-cloud weak Mg II systems are more than an order of magnitude larger than those in Damped Lya systems at z ~ 1.7. In fact, there appears to be a gradual decrease in metallicity with increasing N(HI), from these, the most metal-rich Lya forest clouds, to Lyman limit systems, to sub-DLAs, and finally to the DLAs.

25 pages, 7 figures, accepted by the Astrophysical Journal

References in corpus (10)

• The Mass-Metallicity Relation at z~2
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated?
• A large population of metal-rich, compact, intergalactic C IV absorbers - Evidence for poor small-scale metal mixing
• The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
• The AGN Outflow in the HDFS Target QSO J2233-606 from a High-Resolution VLT/UVES Spectrum
• Metal-rich Damped/sub-Damped Lyman-alpha Quasar Absorbers at z<1
• Elemental Abundance Measurements in Low-redshift Damped Lyman Alpha Absorbers
• The nature of damped Lyman alpha and sub-damped Lyman alpha absorbers
• Physical Properties of Weak MgII Absorbers at z~2

Cited by in corpus (1)

• The Chemical and Ionization Conditions in Weak Mg II Absorbers