The extinction curves of star-forming regions from<i>z</i> = 0.1 to 6.7 using GRB afterglow spectroscopy

Zafar, T.; Watson, Derrick G.; Fynbo, J. P. U.; Malesani, D.; Jakobsson, P.; Postigo, A. de Ugarte

doi:10.1051/0004-6361/201116663

Cited by 136 publications

(218 citation statements)

References 166 publications

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“…This indicates that for at least 10-15% of the extinguished GRBs in our sample, the host galaxy extinction curve has a 2175 Å feature. This is in good agreement with the results from Zafar et al (2011), who studied the extinction curve for a sample of 41 GRB afterglows using combined, broadband Fig. 2.…”

Section: Resultssupporting

confidence: 91%

“…In the latter case the spectral break was modelled as the cooling frequency, ν c , such that the change in slope, δβ, was fixed at 0.5 (Sari et al 1998), and the spectral break was constrained to lie within the UV to X-ray energy range. The physical plausibility of such a change in spectral index is also supported by the analysis of Zafar et al (2011), who did not constrain the spectral slopes in their SED analysis, but found Δβ to be typically ∼0.5. We considered a broken power-law model to provide a better fit to the afterglow spectral continuum when the F-test returned a null hypothesis probability smaller than 5%.…”

Section: Sed Analysismentioning

confidence: 94%

“…GRBs have been particularly effective at probing the dust extinction properties of high-z galaxies thanks to their intrinsically simple spectra Heng et al 2008;Li et al 2008b;Perley et al 2008aPerley et al , 2010Perley et al , 2011Zafar et al 2011). Another novel method of studying extragalactic dust extinction is through the study of early-type galaxies with resolved dust lanes (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The dust extinction curves of gamma-ray burst host galaxies

Schady¹,

Dwelly²,

Page³

et al. 2011

A&A

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The composition and amount of interstellar dust within gamma-ray burst (GRB) host galaxies is of key importance when addressing selection effects in the GRB redshift distribution, and when studying the properties of their host galaxies. As well as the implications for GRB research, probing the dust within the high-z hosts of GRBs also contributes to our understanding of the conditions of the interstellar medium and star-formation in the distant Universe. Nevertheless, the physical properties of dust within GRB host galaxies continues to be a highly contended issue. In this paper we explore the mean extinction properties of dust within the host galaxies of a sample of 17 GRBs with total host galaxy visual extinction A V < 1 ( A V = 0.4), covering a redshift range z = 0.7−3.1. We find the average host extinction curve to have an ultraviolet slope comparable to that of the LMC, but with little evidence of a 2175 Å dust extinction feature as observed along Milky Way and LMC sightlines. We cannot at present rule out the presence of a 2175 Å feature, and both the standard SMC and LMC extinction curves also provide good fits to our data. However, we can reject an extinction curve that has a UV slope as flat as the mean Milky Way extinction curve, whilst also having a 2175 Å feature as prominent as seen in the mean Milky Way extinction curve. This is in contrast to the clear detection of a 2175 Å bump and the flatter extinction curves of some more heavily extinguished GRBs (A V > 1), which may be indicative of there being a dependence between dust abundance and the wavelength dependence of dust extinction, as has been previously speculated.

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Section: Resultssupporting

confidence: 91%

Section: Sed Analysismentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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The dust extinction curves of gamma-ray burst host galaxies

Schady¹,

Dwelly²,

Page³

et al. 2011

A&A

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“…The location of the flux-drop is in the rest-frame ultraviolet and it is therefore natural to explore whether this can be an extreme example of the 2175 Å extinction bump known from the Milky Way and also previously seen in GRB afterglow spectra (Ellison et al 2006;Fynbo et al 2007;Krühler et al 2008;Elíasdóttir et al 2009;Prochaska et al 2009;Zafar et al 2011). This feature is ubiquitous in the MW and in M 31.…”

Section: A Giant 2175-å Extinction Bumpmentioning

confidence: 92%

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

Fynbo

Krühler

Leighly

et al. 2014

A&A

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Context. Gamma-ray burst (GRB) afterglows probe sightlines to star-forming regions in distant star-forming galaxies. Here we present a study of the peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim is to understand the origin of the very unusual properties of the absorption along the line of sight. Methods. We analyse spectroscopic observations obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs 8.8 h and 33 h after the burst, and with imaging from the GROND instrument. We also present imaging and spectroscopy of the host galaxy obtained with the Magellan telescope. Results. The underlying afterglow appears to be a typical afterglow of a long-duration GRB. However, the material along the line of sight has imprinted very unusual features on the spectrum. First, there is a very broad and strong flux drop below 8000 Å (∼4000 Å in the rest frame), which seems to be variable between the two spectroscopic epochs. We can reproduce the flux-drops both as a giant 2175 Å extinction bump and as an effect of multiple scattering on dust grains in a dense environment. Second, we detect absorption lines from excited H i and He i. We also detect molecular absorption from CH + . Conclusions. We interpret the unusual properties of these spectra as reflecting the presence of three distinct regions along the line of sight: the excited He i absorption originates from an H ii-region, whereas the Balmer absorption must originate from an associated photodissociation region.The strong metal line and molecular absorption and the dust extinction must originate from a third, cooler region along the line of sight. The presence of at least three separate regions is reflected in the fact that the different absorption components have different velocities relative to the systemic redshift of the host galaxy.

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“…Those objects are typically relatively high mass, evolved systems. Zafar et al (2011) showed in an analysis of GRB afterglows that GRB host galaxies, which are typically young and star-forming with low metallicities and hard radiation environments (Christensen et al 2004;Castro Cerón et al 2006;Savaglio et al 2009;Svensson et al 2010;Chary et al 2002;Fynbo et al 2008;Watson et al 2010), have substantially lower dust-to-gas ratios than the local group even after accounting for metallicity.…”

Section: Extragalactic Metals-to-dust Ratiosmentioning

confidence: 99%

The Galactic dust-to-metals ratio and metallicity using gamma-ray bursts

Watson

2011

A&A

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112

108

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The metallicity and dust-to-metals ratio of the Galaxy are fundamental parameters in understanding the interstellar medium (ISM). Currently, there is still some uncertainty surrounding these parameters. In this paper, the dust-to-metals ratio in the Galaxy is determined using the photoelectric absorption of the soft X-ray afterglows of a large sample of several hundred gamma-ray bursts (GRBs) to determine the metal column density in combination with Galactic dust maps to determine the line-of-sight dust extinction through the Galaxy in the direction of the GRB. GRB afterglows often have large extragalactic soft X-ray absorptions and therefore the GRB sample's upper-bound will define the Galactic dust-to-metals relation. Using a two-dimensional two-sample Kolmogorov-Smirnoff test, we determine this upper-bound and so derive the dust-to-metals ratio of the Galaxy. We find N H = 2.2 +0.3 −0.4 × 10 21 cm −2 A V asassuming solar, Anders & Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197), metallicity. This result is consistent with previous findings using bright X-ray sources in the Galaxy. Using the same technique but substituting the H i maps from the Leiden-ArgentineBonn survey for the dust maps, allows us to place a limit on the metallicity in the Galaxy. We find a metallicity consistent with the Anders & Grevesse (1989) solar values often used in X-ray fitting. Based on this and previous studies, we suggest that the metallicity of a typical ISM sightline through the Galaxy is ∼0.25 dex higher than the current best estimate of the solar metallicity. We further show that the dust-to-gas ratio seems to be correlated with the total gas column density, and that this may be due to the metallicity gradient observed toward the Galactic centre. Based on the non-constant nature of the dust-to-gas ratio, we propose that the dust column density, at N H = 2.2 × 10 21 cm −2 A V , represents a better proxy for the soft X-ray absorption column density than H i maps.

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The extinction curves of star-forming regions fromz = 0.1 to 6.7 using GRB afterglow spectroscopy

Cited by 136 publications

References 166 publications

The dust extinction curves of gamma-ray burst host galaxies

The dust extinction curves of gamma-ray burst host galaxies

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

The Galactic dust-to-metals ratio and metallicity using gamma-ray bursts

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