Interstellar Abundances in the Magellanic Clouds. I. GHRS Observations of the Small Magellanic Cloud Star Sk 108

Welty, D. E.; Lauroesch, J. T.; Blades, J. C.; Hobbs, L. M.; York, Donald G.

doi:10.1086/304811

Cited by 103 publications

(157 citation statements)

References 102 publications

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“…As with most DLAs, such an abundance pattern is similar to the mean Halo abundance pattern of the Galaxy. However, we note that the Small Magellanic Cloud also has a "Halo-like" depletion pattern (Welty et al 1997), although it is a gas-rich dwarf galaxy. It is therefore hazardous to rely only on the depletion pattern to derive information about the physical origin of the gas, the depletion being more dictated by the metallicity than by the location of the gas in the galaxy.…”

Section: Abundances and Depletionmentioning

confidence: 76%

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Noterdaeme

Petitjean

Pâris

et al. 2014

A&A

Self Cite

107

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We present a study of ∼100 high redshift (z ∼ 2−4) extremely strong damped Lyman-α systems (ESDLA, with N(H i) ≥ 0.5 × 10 22 cm −2 ) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(H i) frequency distribution has a relatively shallow slope with power-law index −3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ∼1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly α emission with L ESDLA (Ly α) (0.6 ± 0.2) × 10 42 erg s −1 in the core of ESDLAs (corresponding to about 0.1 L at z ∼ 2−3), obtained through stacking the fibre spectra (of radius 1 corresponding to ∼8 kpc at z ∼ 2.5). Statistical errors on the Ly α luminosity are of the order of 0.1 × 10 42 erg s −1 but we caution that the measured Ly α luminosity may be overestimated by ∼35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2 × 10 42 erg s −1 . The properties of the Ly α line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-α emitting galaxies (LAEs) with L LAE (Ly α) ≥ 10 41 erg s −1 detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r gas = 2.5 kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly α luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M yr −1 ) ≈ 0.6/ f esc , where f esc < 1 is the Ly α escape fraction. Assuming the typical escape fraction of LAEs, f esc ∼ 0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r gal ≈ 2.5 kpc. Finally, we note that possible overestimation of the Ly α emission would result in both smaller r gas and r gal . Our results support a close association between LAEs and stro...

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Section: Abundances and Depletionmentioning

confidence: 76%

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Noterdaeme

Petitjean

Pâris

et al. 2014

A&A

Self Cite

107

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“…Since Fe is almost completely depleted in diffuse regions of the Milky Way, we are likely to overestimate the ratio of n Si depleted =n Fe depleted in a lower metallicity region, since our prescription for computing n Fe depleted in the Appendix would be an underestimate. This appears to be the case for the SMC, where absorption by clouds along the lines of sight to Sk 108 and Sk 155 shows ½Si=Zn ¼ 0, implying a lack of silicon depletion, but ½Si=Fe ¼ 0:5, indicating that iron is significantly depleted (Welty et al 1997(Welty et al , 2001). In the diffuse regions of the Galaxy modeled by Weingartner & Draine (2001a), 75% of the Si atoms and 95% of the Fe atoms are depleted, but in the SMC it appears that no more than 20% of the Si atoms are depleted even though 70% of…”

Section: No 1 2003mentioning

confidence: 82%

Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Wolfe

Prochaska

Gawiser

2003

ApJ

160

261

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We describe a technique that for the first time measures star formation rates (SFRs) in damped Ly systems (DLAs) directly. We assume that massive stars form in DLAs and that the far-ultraviolet (FUV) radiation they emit heats the gas by the grain photoelectric mechanism. We infer the heating rate by equating it to the cooling rate measured by the strength of C ii* 1335.7 absorption. Since the heating rate is proportional to the product of the dust-to-gas ratio, the grain photoelectric heating efficiency, and the SFR per unit area, _ Ã Ã , we can deduce _ Ã Ã for DLAs in which the cooling rate and dust-to-gas ratio have been measured. We consider models in which the dust consists of carbonaceous grains and silicate grains. We present twophase models in which the cold neutral medium (CNM) and warm neutral medium (WNM) are in pressure equilibrium. In the CNM model the line of sight passes through CNM and WNM gas, while in the WNM model the line of sight passes only through WNM gas. Since the grain photoelectric heating efficiency is at least an order of magnitude higher in the CNM than in the WNM, most of the C ii* absorption arises in the CNM in the CNM model. We use the measured C ii* absorption lines to derive _ Ã Ã for a sample of %30 DLAs in which has been inferred from element depletion patterns. We show that the inferred _ Ã Ã corresponds to an average over the star-forming volume of the DLA rather than to local star formation along the line of sight. We obtain the average _ Ã Ã and show that _ Ã Ã ¼ 10 À2:2 M yr À1 kpc À2 for the CNM solution and _ Ã Ã ¼ 10 À1:3 M yr À1 kpc À2 for the WNM solution. Interestingly, the SFR per unit area in the CNM solution is similar to that measured in the Milky Way interstellar medium.

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“…Unfortunately, the differential depletion characteristics of cold, dense gas in other galaxies (e.g., the Magellanic Clouds) have not been extensively measured, in part because dust obscuration challenges the analysis. In the Small Magellanic Cloud (SMC), one does observe highly depleted gas along the sight line to Sk 155, but one also finds modest depletions in clouds where C i analysis indicates a large density (>100 cm À3 ; Welty et al 2001Welty et al , 2006Sofia et al 2006). We cautiously conclude that the depletion levels observed for the GRB DLAs are generally lower than that observed for cold, dense clouds in the local universe.…”

Section: General Characteristics Of the Ism Near Star-forming Regionsmentioning

confidence: 99%

“…We make this choice because (1) no GRB DLA to date has exhibited the 2175 8 dust feature characteristic of the Milky Way and Large Magellanic Cloud (LMC) extinction laws (e.g., Mirabal et al 2002;Savaglio & Fall 2004;Ellison et al 2006); and (2) the metallicities of GRB DLAs are representative of the SMC. We derive the dust-to-gas ratio of the DLAs relative to the SMC: / SMC by assuming that the SMC has metallicity ½M/H SMC ¼ À0:7 and that 90% of its refractory elements are depleted from the gas phase, i.e., ½M/Fe SMC ¼ þ1 ( Welty et al 1997( Welty et al , 2001. In this case, the relative dust-to-gas ratio is Table 3.…”

Section: Comparisons With Qso Dlasmentioning

confidence: 99%

Probing the Interstellar Medium near Star‐forming Regions with Gamma‐Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust

Prochaska

Chen

Dessauges‐Zavadsky

et al. 2007

ApJ

217

306

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We study the chemical abundances of the interstellar medium surrounding high-z gamma-ray bursts (GRBs) through analysis of the damped Ly systems ( DLAs) identified in afterglow spectra. These GRB DLAs are characterized by large H i column densities N H i and metallicities [M/H] spanning 1/100 to nearly solar, with median ½M/H > À1 dex. The majority of GRB DLAs have [M/H] values exceeding the cosmic mean metallicity of atomic gas at z > 2; i.e., if anything, the GRB DLAs are biased to larger metallicity. We also observe (1) large [Zn/Fe] values (> +0.6 dex) and subsolar Ti/Fe ratios, which imply substantial differential depletion; (2) large /Fe ratios, suggesting nucleosynthetic enrichment by massive stars; and (3) low C 0 /C + ratios (<10 À4 ). Quantitatively, the observed depletion levels and C 0 /C + ratios of the gas are not characteristic of cold, dense H i clouds in the Galactic interstellar medium (ISM). We argue that the GRB DLA represents the ISM near the GRB but not gas directly local to the GRB (e.g., its molecular cloud or circumstellar material). We compare these observations with DLAs intervening in background quasars (QSO DLAs). The GRB DLAs exhibit larger N H i values, higher /Fe and Zn/Fe ratios, and higher metallicity than the QSO DLAs. Although these differences are statistically significant, the offsets are relatively modest (N H i excepted). We argue that the differences result primarily from galactocentric radius-dependent differences in the ISM: GRB DLAs preferentially probe denser, more depleted, higher metallicity gas located in the inner few kiloparsecs, whereas QSO DLAs are more likely to intersect the less dense, less enriched, outer regions of the galaxy. Finally, we investigate whether dust obscuration may exclude GRB DLA sight lines from QSO DLA samples; we find that the majority of GRB DLAs would be recovered, which implies little observational bias against large N H i systems.

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Interstellar Abundances in the Magellanic Clouds. I. GHRS Observations of the Small Magellanic Cloud Star Sk 108

Cited by 103 publications

References 102 publications

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Probing the Interstellar Medium near Star‐forming Regions with Gamma‐Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust

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