The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25<sup>∗</sup>

Zafar, T.; Heintz, K. E.; Fynbo, J. P. U.; Malesani, D.; Bolmer, J.; Ledoux, C.; Arabsalmani, M.; Kaper, L.; Campana, S.; Starling, R. L. C.; Selsing, J.; Канн, Д. А.; Postigo, A. de Ugarte; Schweyer, T.; Christensen, L.; Møller, P.; Japelj, J.; Perley, D.; Tanvir, N. R.; D’Avanzo, P.; Hartmann, D. H.; Hjorth, J.; Covino, S.; Sbarufatti, B.; Jakobsson, P.; Izzo, L.; Salvaterra, R.; D’Elia, V.; Xu, Dawei

doi:10.3847/2041-8213/aaca3f

Cited by 26 publications

(43 citation statements)

References 48 publications

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“…The sample of GRBs studied here was built by extracting all bursts from the VLT/X-shooter GRB (XS-GRB) afterglow legacy survey (Selsing et al 2018), combined with the GRB afterglow sample of Fynbo et al (2009, hereafter F09). We also include the recent discovery of a strong C i absorber towards GRB 180325A, which also shows a prominent 2175 Å dust extinction feature (Zafar et al 2018a). We subsequently imposed additional observational selection criteria to exclude late-time host galaxy observations and afterglow spectra with poor spectral quality or low spectral resolution.…”

Section: The Grb Samplementioning

confidence: 99%

Cold gas in the early Universe

Heintz

Ledoux

Fynbo

et al. 2018

A&A

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We present a survey for neutral atomic-carbon (C I) along gamma-ray burst (GRB) sightlines, which probes the shielded neutral gas-phase in the interstellar medium (ISM) of GRB host galaxies at high redshift. We compile a sample of 29 medium- to high-resolution GRB optical afterglow spectra spanning a redshift range through most of cosmic time from 1 < z < 6. We find that seven (≈25%) of the GRBs entering our statistical sample have C I detected in absorption. It is evident that there is a strong excess of cold gas in GRB hosts compared to absorbers in quasar sightlines. We investigate the dust properties of the GRB C I absorbers and find that the amount of neutral carbon is positively correlated with the visual extinction, AV, and the strength of the 2175 Å dust extinction feature, Abump. GRBs with C I detected in absorption are all observed above a certain threshold of logN(H I)/cm−2 + [X/H] > 20.7 and a dust-phase iron column density of logN(Fe)dust/cm−2 > 16.2. In contrast to the SED-derived dust properties, the strength of the C I absorption does not correlate with the depletion-derived dust properties. This indicates that the GRB C I absorbers trace dusty systems where the dust composition is dominated by carbon-rich dust grains. The observed higher metal and dust column densities of the GRB C I absorbers compared to H2- and C I-bearing quasar absorbers is mainly a consequence of how the two absorber populations are selected, but is also required in the presence of intense UV radiation fields in actively star-forming galaxies.

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Section: The Grb Samplementioning

confidence: 99%

Cold gas in the early Universe

Heintz

Ledoux

Fynbo

et al. 2018

A&A

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“…The UV bump, first observed in the 1960s (Stecher 1965a), is a broad ultraviolet absorption bump observed on the interstellar medium extinction curves from the Milky Way to high-redshift galaxies, with a stable position centered at 217.5 nm, although showing variations in intensity and width in different lines of sight (Bless & Savage 1972;Fitzpatrick & Massa 1986Gordon et al 2003;Elíasdóttir et al 2009;Clayton et al 2015;Zafar et al 2018;Fitzpatrick et al 2019, and references therein). This spectral feature has long been assigned to π→π * transitions specific to sp 2 conjugated carbon bonding of graphite particles or polycyclic aromatic hydrocarbons (Mishra & Li 2015.…”

Section: Introductionmentioning

confidence: 98%

Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

Dubosq

Calvo

Rapacioli

et al. 2020

A&A

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Context. The UV bump observed in the interstellar medium extinction curve of galaxies has been assigned to π → π⋆ transitions within the sp2 conjugated network of carbon grains. These grains are commonly thought to be graphitic particles or polycyclic aromatic hydrocarbons. However, questions are still open regarding the shape and degree of amorphization of these particles, which could account for the variations in the 2175 Å astronomical bump. Optical spectra of graphitic and onion-like carbon structures were previously obtained from dielectric constant calculations based on oscillating dipole models. In the present study, we compute the optical spectra of entire populations of carbon clusters using an explicit quantum description of their electronic structure for each individual isomer. Aims. Our aim is to determine the optical spectra of pure carbon clusters Cn=24,42,60 sorted into structural populations according to specific order parameters, namely asphericity and sp2 fraction, and to correlate these order parameters to the spectral features of the band in the region of the UV bump. Our comparison involves data measured for the astronomical UV bump as well as experimental spectra of carbon species formed in laboratory flames. Methods. The individual spectrum of each isomer is determined using the time-dependent density functional tight-binding method. The final spectrum for a given population is obtained by averaging the individual spectra for all isomers of a given family. Our method allows for an explicit description of particle shape, as well as structural and electronic disorder with respect to purely graphitic structures. Results. The spectra of the four main populations of cages, flakes, pretzels, and branched structures (Dubosq et al. 2019, A&A, 625, L11) all display strong absorption in the 2–8 eV domain, mainly due to π → π⋆ transitions. The absorption features, however, differ from one family to another and our quantum modeling indicates that the best candidates for the interstellar UV bump at 217.5 nm are cages and then flakes, while the opposite trend is found for the carbonaceous species formed in flame experiments; the other two families of pretzels and branched structures play a lesser role in both cases. Conclusions. Our quantum modeling shows the potential contribution of carbon clusters with a high fraction of conjugated sp2 atoms to the astronomical UV bump and to the spectrum of carbonaceous species formed in flames. While astronomical spectra are better accounted for using rather spherical isomers such as cages, planar flake structures are involved as a much greater component in flame experiments. Interestingly, these flake isomers have been proposed as likely intermediates in the formation mechanisms leading to buckminsterfullerene, which was recently detected in space. This study, although restricted here to the case of pure carbon clusters, will be extended towards several directions of astronomical relevance. In particular, the ability of the present approach to deal with large-scale molecular systems at an explicit quantum level of electronic structure and its transferable character towards different charge states and the possible presence of heteroatoms makes it the method of choice to address the important case of neutral and ionic hydrogenated compounds.

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“…The best fit F&M 90 extinction curve parameters for the X-ray to the optical/near-infrared afterglow SEDs of the GRB C i absorbers. The best fit curve coefficients are from a Zafar et al (2018a), b Zafar et al (2018c) or derived in this work. Notes.…”

Section: Sed Analysismentioning

confidence: 99%

On the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bump

Heintz

Zafar

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present a study of the extinction and depletion-derived dust properties of gamma-ray burst (GRB) absorbers at 1 < z < 3 showing the presence of neutral carbon (C i). By modelling their parametric extinction laws, we discover a broad range of dust models characterizing the GRB C i absorption systems. In addition to the already well-established correlation between the amount of C i and visual extinction, A V , we also observe a correlation with the total-toselective reddening, R V . All three quantities are also found to be connected to the presence and strength of the 2175 Å dust extinction feature. While the amount of C i is found to be correlated with the SED-derived dust properties, we do not find any evidence for a connection with the depletion-derived dust content as measured from [Zn/Fe] and N(Fe) dust . To reconcile this, we discuss a scenario where the observed extinction is dominated by the composition of dust particles confined in the molecular gas-phase of the ISM. We argue that since the depletion level trace non-carbonaceous dust in the ISM, the observed extinction in GRB C i absorbers is primarily produced by carbon-rich dust in the molecular cloud and is therefore only observable in the extinction curves and not in the depletion patterns. This also indicates that the 2175 Å dust extinction feature is caused by dust and molecules in the cold and molecular gas-phase. This scenario provides a possible resolution to the discrepancy between the depletion-and SED-derived amounts of dust in high-z absorbers.

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The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25^∗

Cited by 26 publications

References 48 publications

Cold gas in the early Universe

Cold gas in the early Universe

Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

On the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bump

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The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25∗

Cited by 26 publications

References 48 publications

Cold gas in the early Universe

Cold gas in the early Universe

Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

On the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bump

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Product

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The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25^∗