A Survey of Weak Mg<scp>ii</scp>Absorbers at Redshift 〈<i>z</i>〉 = 1.78

Lynch, R.; Charlton, Jane C.; Kim, Tae Sun

doi:10.1086/499261

Cited by 23 publications

(39 citation statements)

References 25 publications

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“…While intermediate-strength systems show no evolution to within fairly strong limits over the large range 0:5 P z P 2 ( Fig. 5; also see NTR05 for discussion), there is evidence that the incidence of weak systems exhibits a significant decrease above z % 1 (Lynch et al 2006). It should also be noted, however, that most single-cloud systems have W k2796 0 < 0:1 8 (the limit of this study).…”

Section: Population-dependent Evolutionmentioning

confidence: 54%

MMT Survey for Intervening MgiiAbsorption

Nestor

Turnshek

Rao

2006

ApJ

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We present the results from a spectroscopic survey for intervening Mg ii absorption in the spectra of 381 background QSOs conducted at the MMT telescope. This survey complements our earlier SDSS EDR Mg ii survey, extending our results to lower redshift (z ' 0:15) and weaker Mg ii k2796 rest equivalent width (W k2796 0 ' 0:1 8). We confirm two major results from that survey: the transition in the W k2796 0 distribution at W k2796 0 % 0:3 8, and the W k2796 0 -dependent evolution of the incidence of systems. The nature of @ 2 N /@z@W k2796 0 is consistent with the idea that multiple physically distinct components/processes contribute to the incidence of Mg ii absorption systems in a W 0 -dependent manner and evolve at different rates. A significant decrease in the total proper absorption cross section is detected in our MMT data for systems as weak as 1:0 8 W k2796 0 < 1:5 8 at z P 0:4. We discuss this W 0 -dependent evolution in the context of the evolution of galaxy structures, processes including superwinds and interactions, and damped-Ly absorbers. We also consider the possibility that the observed redshift and W k2796 0 dependence of the incidence of absorption in spectroscopic surveys for low-ionization/neutral gas results from the effects of dust-induced extinction.

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Section: Population-dependent Evolutionmentioning

confidence: 54%

MMT Survey for Intervening MgiiAbsorption

Nestor

Turnshek

Rao

2006

ApJ

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“…(following Churchill et al 1999), we found 28 systems in a redshift path ∆z = 13.6 (see also Lynch et al 2006). We also examined the sample of Churchill et al (1999) observed with HIRES at Keck, in the same redshift range, at a similar resolution, but in general at a lower signal-to-noise ratio.…”

Section: Comparison With Weak Mg II Systemsmentioning

confidence: 69%

A cold metal-poor cloud traced by a weak Mg II absorption at z $\mathsfsl{\simeq}$ 0.45

D’Odorico¹

2007

A&A

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Aims. We present the observations of a weak Mg ii absorption system detected at z ∼ 0.452 in the UVES high-resolution spectrum of the QSO HE0001-2340. The weaker of the two Mg ii components forming the system shows associated absorptions due to Si i, Ca i, and Fe i observed for the first time in a QSO spectrum. We investigate the nature of this absorber by comparing its properties with those of different classes of absorbers and reproducing its ionization conditions with photoionization models.Methods. We measured column densities of Mg i, Mg ii, Si i, Ca i, Ca ii, Mn ii, Fe i, and Fe ii with Voigt profile fitting. Although most of the observed velocity profiles are not resolved in the UVES spectrum, a curve of growth analysis excluded a significant underestimation of the column densities, in particular for the Fe ii and Mg ii multiplets. We compared our measurements with a sample of 28 weak Mg ii systems detected in the interval 0.4 < z < 1.4 in the 18 UVES spectra of the ESO Large Programme, plus 24 weak Mg ii systems in the same redshift range taken from the literature. Then, we performed a comparison with 11 damped systems for which ionic column densities were measured component by component and with 44 Galactic lines of sight with measured Ca i, Ca ii and Fe i. We also ran a grid of photoionization models with Cloudy to reproduce the observed Mg i/Mg ii, Ca i/Ca ii, and Fe i/Fe ii column density ratios for the studied system. Results. The observed absorber belongs to the class of weak Mg ii systems on the basis of its equivalent width, however the relative strength of commonly observed transitions deviates significantly from those of the above mentioned absorbers. A rough estimate of the probability of crossing such a system with a QSO line of sight is P ∼ 0.03. The presence of rare neutral transitions suggests that the cloud is shielded by a large amount of neutral hydrogen. A detailed comparison of the observed column densities with the average properties of damped Lyman-α systems and local interstellar cold clouds shows, in particular, deficient Mg ii/Mg i and Ca ii/Ca i ratios in our cloud. The results of photoionization models indicate that the cloud could be ionized by the UV background.However, a simple model of a single cloud with uniform density cannot reproduce the observed ionic abundance ratios, suggesting a more complex density structure for the absorber. Supposing that ionization corrections are negligible, the most puzzling result is the underabundance of magnesium with respect to iron which is hard to explain both with nucleosynthesis and with differential dust depletion.

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“…In addition, Lynch et al (2006) and Narayanan et al (2007) discovered an evolution in the redshift number density (dN /dz) of weak Mg ii absorbers over the interval 0:4 < z < 2:4. The dN /dz was found to peak at z ¼ 1:2, and subsequently decline (from a no-evolution trend) toward higher redshift.…”

Section: à3mentioning

confidence: 99%

The Chemical and Ionization Conditions in Weak MgiiAbsorbers

Narayanan

Charlton

Misawa

et al. 2008

Astrophysical Journal

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We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg ii absorbers identified in the VLT/UVES archive of quasar spectra. In addition to Mg ii, we present equivalent width and column density measurements of other low ionization species such as Mg i, Fe ii, Al ii, C ii, Si ii, and also Al iii. We find that the column densities of C ii and Si ii are strongly correlated with the column density of Mg ii, with minimal scatter in the relationships. The column densities of Fe ii exhibit an appreciable scatter when compared with the column density of Mg ii, with some fraction of clouds having N (Fe ii) $ N (Mg ii), in which case the density is constrained to n H > 0:05 cm À3. Other clouds in which N (Fe ii)TN (Mg ii) have much lower densities. From ionization models, we infer that the metallicity in a significant fraction of weak Mg ii clouds is constrained to values of solar or higher, if they are sub-Lyman-limit systems. Based on the observed constraints, we hypothesize that weak Mg ii absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg ii clouds, those in which N (Fe ii)TN (Mg ii), identified at both low (z $ 1) and high (z $ 2) redshift, are likely to be tracing gas in the extended halos of galaxies, analogous to the Galactic high-velocity clouds. These absorbers might correspond to -enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. The N(Mg ii) and N(Fe ii)/N(Mg ii) in such clouds are also closely comparable to those measured for the high-velocity components in strong Mg ii systems. An evolution is found in N(Fe ii)/N(Mg ii) from z ¼ 2:4 to z ¼ 0:4, with an absence of weak Mg ii clouds with N (Fe ii) $ N (Mg ii) at high-z. The N (Fe ii) $ N (Mg ii) clouds, which are prevalent at lower redshifts (z < 1:5), must be tracing Type Ia enriched gas in small, high-metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.

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A Survey of Weak MgiiAbsorbers at Redshift 〈z〉 = 1.78

Cited by 23 publications

References 25 publications

MMT Survey for Intervening MgiiAbsorption

MMT Survey for Intervening MgiiAbsorption

A cold metal-poor cloud traced by a weak Mg II absorption at z $\mathsfsl{\simeq}$ 0.45

The Chemical and Ionization Conditions in Weak MgiiAbsorbers

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