VLT/UVES observations of peculiar<i>α</i>abundances in a sub-DLA at<i>z</i>≈ 1.8 towards the quasar B1101−26

Fox, A. J.; Richter, Philipp; Fechner, C.

doi:10.1051/0004-6361/201423825

Cited by 12 publications

(14 citation statements)

References 84 publications

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“…While [Si/Al] is expected to display such an enhanced odd-even effect, any claims based on our current data would be premature; [Mg/Al] is another ratio predicted to reflect the signature of an enhanced odd-even effect (Heger & Woosley 2002). Complementary to an enhanced odd-even effect, one would expect to see α-element enhancement relative to iron typical in gas enriched by Type II supernovae (Wheeler et al 1989;Fox et al 2014). Furthermore, while Mg II and Fe II have similar dust depletion factors in DLAs (De Cia et al 2016), iron is more refractory and its abundance ratios can affirm that depletion is not significant in LLSs.…”

Section: Non-solar Aluminum Abundance Ratiosmentioning

confidence: 67%

“…While the lack of saturation may come as a surprise, there are numerous examples in the literature of highredshift LLSs (and even some super-LLSs/sub-DLAs) observed at higher spectral resolution in which the lines we use are unsaturated (Richter et al 2005;Simon & Hamann 2010;Prochter et al 2010;Fox et al 2014;Prochaska et al 2015). At these redshifts, optically thick systems showing saturation in the lines we use are typically at higher N H I (e.g., Prochaska et al 2006) and/or have unusually high metallicities (Crighton et al 2015).…”

Section: H I and Metal Ion Column Density Measurementsmentioning

confidence: 99%

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Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at Z = 3.7

Glidden

Cooper

Cooksey

et al. 2016

ApJ

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We measured metallicities for 33 z = 3.4-4.2 absorption line systems drawn from a sample of H I-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of H I column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, finding ionization-corrected metallicities or upper limits. Interestingly, our ionization models were better constrained with enhanced α-to-aluminum abundances, with a median abundance ratio of [α/Al]=0.3. Measured metallicities were generally low, ranging from [M/H]=−3 to −1.68, with even lower metallicities likely for some systems with upper limits. Using survival statistics to incorporate limits, we constructed the cumulative distribution function (CDF) for LLS metallicities. Recent models of galaxy evolution propose that galaxies replenish their gas from the low-metallicity intergalactic medium (IGM) via high-density H I "flows" and eject enriched interstellar gas via outflows. Thus, there has been some expectation that LLSs at the peak of cosmic star formation (z≈3) might have a bimodal metallicity distribution. We modeled our CDF as a mix of two Gaussian distributions, one reflecting the metallicity of the IGM and the other representative of the interstellar medium of star-forming galaxies. This bimodal distribution yielded a poor fit. A single Gaussian distribution better represented the sample with a low mean metallicity of [M/H]≈−2.5.

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Section: Non-solar Aluminum Abundance Ratiosmentioning

confidence: 67%

Section: H I and Metal Ion Column Density Measurementsmentioning

confidence: 99%

Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at Z = 3.7

Glidden

Cooper

Cooksey

et al. 2016

ApJ

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“…As a result, the preferred model gives a metallicity half of that of the MW ISM and a radiation field 10 times the intensity of the MW ISM radiation. As is often the case, the modeling predicts too much C ii (Fox, Richter & Fechner 2014). The predicted neutral carbon column density increases as n(H i) rises.…”

Section: Cloudy Photoionization Modelingmentioning

confidence: 83%

Cold gas and a Milky Way-type 2175-Å bump in a metal-rich and highly depleted absorption system

Caucal

Noterdaeme

et al. 2015

Mon. Not. R. Astron. Soc.

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We report the detection of a strong Milky Way-type 2175Å extinction bump at z = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey (SDSS) Data Release 10. We conduct follow up observations with the Echelle Spectrograph and Imager (ESI) onboard the Keck-II telescope and the Ultraviolet and Visual Echelle Spectrograph (UVES) on the VLT. This 2175Å absorber is remarkable in that we simultaneously detect neutral carbon (C i), neutral chlorine (Cl i), and carbon monoxide (CO). It also qualifies as a damped Lyman alpha system. The J1211+0833 absorber is found to be metal-rich and has a dust depletion pattern resembling that of the Milky Way disk clouds. We use the column densities of the C i fine structure states and the C ii/C i ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A Cloudy photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold (T ∼ 100 K) neutral medium with a high density (n(H i) ∼ 100 cm −3 ) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C i, CO, and the 2175Å bump, combined with the high metallicity, high dust depletion level and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population.

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“…Now, the observed carbon and oxygen column densities match the Cloudy predicitions. The remaining ion species show minor discrepancies that can have various reason as we discussed in Fox et al (2014). In any case, it is obvious that the hydrogen density of this gas cloud must be relatively high, n H 10 −1.5 cm −3 .…”

Section: Weakly Ionised Absorbermentioning

confidence: 83%

A high-redshift quasar absorber without C IV. A galactic outflow caught in the act?

Fox

Richter

2016

A&A

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We present a detailed analysis of a very unusual sub-damped Lyman α (sub-DLA) system at redshift z = 2.304 towards the quasar Q 0453 − 423, based on high signal-to-noise (S/N), high-resolution spectral data obtained with VLT/UVES. With a neutral hydrogen column density of log N(H ) = 19.23 and a metallicity of −1.61 as indicated by [O /H ] the sub-DLA mimics the properties of many other optically thick absorbers at this redshift. A very unusual feature of this system is, however, the lack of any C  absorption at the redshift of the neutral hydrogen absorption, although the relevant spectral region is free of line blends and has very high S/N. Instead, we find high-ion absorption from C  and O  in another metal absorber at a velocity more than 220 km s −1 redwards of the neutral gas component. We explore the physical conditions in the two different absorption systems using Cloudy photoionisation models. We find that the weakly ionised absorber is dense and metal-poor while the highly ionised system is thin and more metal-rich. The absorber pair towards Q 0453 − 423 mimics the expected features of a galactic outflow with highly ionised material that moves away with high radial velocities from a (proto)galactic gas disk in which star-formation takes place. We discuss our findings in the context of C  absorption line statistics at high redshift and compare our results to recent galactic-wind and outflow models.

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VLT/UVES observations of peculiarαabundances in a sub-DLA atz≈ 1.8 towards the quasar B1101−26

Cited by 12 publications

References 84 publications

Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at Z = 3.7

Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at Z = 3.7

Cold gas and a Milky Way-type 2175-Å bump in a metal-rich and highly depleted absorption system

A high-redshift quasar absorber without C IV. A galactic outflow caught in the act?

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