PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $\mu$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $\mu$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&

Les Bandes Interstellaires Diffuses (DIBs) : de nouvelles solutions pour un problème ancien

Diffuse interstellar bands (DIBs) represent a century-old mystery: none of the hundreds of bands could be identified with certainty with a specific carrier, at the very likely exception of the buckminsterfullerene cation C60+. Identifying and quantifying the amount of the large interstellar carbonaceous molecules that are very likely responsible for the DIBs is mandatory: DIB carriers likely represent the largest amount of organic matter in the Universe and are an important piece of the chain of processes that govern the interstellar/stellar cycle.Up to recently, most of the DIB studies have had as a unique goal the identification of the carriers, and to do so have been focusing on a limited number of hot, distant and reddened stars, using increasingly powerful instruments. This thesis marks a turning point in the methods and goals associated with the DIBs, an evolution allowed and motivated by the increasing number of stellar surveys with high multiplex instruments. As a matter of fact, it is possible today to gather massive amounts of data, both from the point of view of the number of target stars and from the point of view of the number of DIBs simultaneously observed. This has opened the way to new types of studies, more ambitious goals, and, importantly, new potential comparisons with laboratory data. This thesis presents a large number of DIB extractions and four of these novel analyses :- Methods of extraction and search for new DIBs.- Statistical studies of the link between DIB strengths and the physical properties of their hosting clouds.- Tomographic studies of the carriers on large and small spatial scales.- Line profile extractions based on carefully selected sightlines, studies of their substructures and spatial variability and subsequent constraints on their potential molecular carriers.Les bandes interstellaires diffuses (DIBs) représentent un mystère centenaire : aucune des centaines de bandes n'a pu être identifiée avec certitude avec un porteur spécifique, à l'exception très probable du cation buckminsterfullerène C60+. Il est obligatoire d'identifier et de quantifier la quantité de grosses molécules carbonées interstellaires qui sont très probablement responsables des DIBs : Les porteurs de DIB représentent probablement le plus grand réservoir de matière organique dans le Milieu interstellaire (MIS) et constituent un élément important de la chaîne des processus qui régissent le cycle interstellaire/stellaire. Jusqu'à récemment, la plupart des études liées aux DIBs avaient pour objectif unique l'identification des porteurs et, pour ce faire, se concentraient sur un nombre limité d'étoiles chaudes, distantes et rougies. Mon travail de recherche en thèse marque un tournant dans les méthodes et les objectifs associés aux DIBs, une évolution permise et motivée par le nombre croissant de relevés stellaires avec des instruments de plus en plus puissants à haute résolution spectrale. En effet, il est aujourd'hui possible de recueillir des quantités massives de données, tant du point de vue du nombre d'étoiles cibles que du point de vue du nombre de DIBs observées simultanément. Cela a ouvert la voie à de nouveaux types d'études, à des objectifs plus ambitieux et, surtout, à de nouvelles comparaisons potentielles avec les données de laboratoire. Ma thèse présente un grand nombre d'extractions de DIBs et quatre de ces nouvelles analyses :- Méthodes d'extraction et recherche de nouvelles DIBs.- Lien avec les propriétés physiques des nuages.- Constitution de bases de données pour la cartographie du MIS.- Tomographie des structures individuelles.- Des extractions de profils de DIBs basées sur des lignes de visée soigneusement sélectionnées, des études de leurs sous-structures et de leur variabilité spatiale et des contraintes subséquentes sur leurs porteurs moléculaires potentiels

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

International audience(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $μ$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $μ$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $μ$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'