17 research outputs found
PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
The JWST has captured the most detailed and sharpest infrared images ever
taken of the inner region of the Orion Nebula, the nearest massive star
formation region, and a prototypical highly irradiated dense photo-dissociation
region (PDR). We investigate the fundamental interaction of far-ultraviolet
photons with molecular clouds. The transitions across the ionization front
(IF), dissociation front (DF), and the molecular cloud are studied at
high-angular resolution. These transitions are relevant to understanding the
effects of radiative feedback from massive stars and the dominant physical and
chemical processes that lead to the IR emission that JWST will detect in many
Galactic and extragalactic environments. Due to the proximity of the Orion
Nebula and the unprecedented angular resolution of JWST, these data reveal that
the molecular cloud borders are hyper structured at small angular scales of
0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are
observed such as ridges, waves, globules and photoevaporated protoplanetary
disks. At the PDR atomic to molecular transition, several bright features are
detected that are associated with the highly irradiated surroundings of the
dense molecular condensations and embedded young star. Toward the Orion Bar
PDR, a highly sculpted interface is detected with sharp edges and density
increases near the IF and DF. This was predicted by previous modeling studies,
but the fronts were unresolved in most tracers. A complex, structured, and
folded DF surface was traced by the H2 lines. This dataset was used to revisit
the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a
complete view of the PDR, all the way from the PDR edge to the substructured
dense region, and this allowed us to determine, in detail, where the emission
of the atomic and molecular lines, aromatic bands, and dust originate
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 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 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 m AIB emission from class B in
the molecular PDR to class A 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&
PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars
22 pags., 8 figs., 1 tab.Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter-and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.Support for JWST-ERS program ID 1288 was provided through grants from the STScI under NASA contract NAS5-03127 to STScI (K.G., D.V.D.P., M.R.), Univ. of Maryland (M.W., M.P.), Univ. of Michigan (E.B., F.A.), and Univ. of Toledo (T.S.-Y.L.). O.B. and E.H. are supported by the Programme National âPhysique et Chimie du Milieu Interstellaireâ (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES, and through APR grants 6315 and 6410 provided by CNES. E. P. and J.C. acknowledge support from the National Science and
Engineering Council of Canada (NSERC) Discovery Grant program (RGPIN-2020-06434 and RGPIN-2021-04197 respectively). E.P. acknowledges support from a Western Strategic Support Accelerator Grant (ROLA ID 0000050636). J.R.G. and S.C. thank the Spanish MCINN for funding support under grant PID2019-106110GB-I00. Work by M.R. and Y.O. is carried out within the Collaborative Research Centre 956, subproject C1, funded by the Deutsche Forschungsgemeinschaft (DFG)âproject ID 184018867. T.O. acknowledges support from JSPS Bilateral Program, grant No. 120219939. M.P. and M.W. acknowledge support from NASA Astrophysics Data Analysis Program award #80NSSC19K0573. C.B. is grateful for an appointment at NASA Ames Research Center through the San JosĂ© State University Research Foundation (NNX17AJ88A) and acknowledges support from the Internal Scientist Funding Model (ISFM) Directed Work Package at
NASA Ames titled: âLaboratory AstrophysicsâThe NASA Ames PAH IR Spectroscopic Database.âPeer reviewe
Ăvolution des poussiĂšres interstellaires dans les rĂ©gions photon-dominĂ©es
Micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size, and shape) and play a key role in numerous phenomena in the interstellar medium (ISM). The large disparity in physical conditions (i.e. density and gas temperature) in the ISM triggers an evolution of dust properties.The analysis of how dust evolves with the physical conditions is a stepping stone towards amore thorough understanding of interstellar dust. As physical conditions vary widely and are spatially resolved in nearby photon-dominated regions (PDRs), they are the ideal place to study dust evolution as a function of physical conditions. In this thesis, I focus on how does interstellar dust evolves with physical conditions in nearby PDRs. To this end, I modelled dust emission and scattering using the THEMIS interstellar dust model together withthe 3D radiative transfer code SOC. I used Spitzer and Herschel observations to confront the results of my modelling in order to constrain the dust properties. I found that nano-grains are strongly depleted in the outer irradiated part of the Horsehead and that grains coagulate together to form aggregates in the inner dense part of the Horsehead.I proposed a scenario where in the outer part of the Horsehead nebula, all the nano-grain have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallestof the nano-grain that are sensitive to the radiation field are photo-destroyed. In the inner part of the Horsehead nebula, grains most likely consist of multi-compositional mantled aggregates, as would expected in high density regions.Les processus microphysiques Ă la surface des poussiĂšres interstellaires sont Ă©troitement liĂ©s Ă leurs propriĂ©tĂ©s (i.e. la taille et la forme des poussiĂšres) et jouent un rĂŽle clĂ© dans de nombreux phĂ©nomĂšnes du milieu interstellaire (MIS). La grande disparitĂ© des conditions physiques (i.e. la densitĂ© et la tempĂ©rature du gaz) dans le MIS dĂ©clenche une Ă©volution des propriĂ©tĂ©s des poussiĂšres. L'analyse de l'Ă©volution de la poussiĂšre en fonction des conditions physiques est un tremplin vers une comprĂ©hension plus approfondie de la poussiĂšre interstellaire. Ătant donnĂ© que les conditions physiques varient considĂ©rablement et sont spatialement rĂ©solues dans les rĂ©gions photon-dominĂ©es (PDRs) proches, elles constituent le lieu idĂ©al pour Ă©tudier l'Ă©volution de la poussiĂšre en fonction des conditions physiques. Dans cette thĂšse, je me concentre sur la façon dont la poussiĂšre interstellaire Ă©volue en fonction des conditions physiques dans les PDRs proches. Ă cette fin, j'ai modĂ©lisĂ© l'Ă©mission et la diffusion de la poussiĂšre en utilisant le modĂšle de poussiĂšre interstellaire THEMIS ainsi que le code de transfert radiatif 3D SOC. J'ai utilisĂ© les observations Spitzer et Herschel pour confronter les rĂ©sultats de ma modĂ©lisation afin de contraindre les propriĂ©tĂ©s de la poussiĂšre. J'ai constatĂ© que les nano-grains sont fortement dĂ©plĂ©tĂ©s dans la partie irradiĂ©e de la tĂȘte de cheval et que les grains coagulent pour former des agrĂ©gats dans la partie dense de la tĂȘte de cheval. J'ai proposĂ© un scĂ©nario dans lequel, dans la partie irradiĂ©e de la nĂ©buleuse de la tĂȘte de cheval, tous les nano-grains n'ont pas encore eu le temps de se reformer par la photofragmentation des agrĂ©gats et les plus petits des nano-grains sensibles au champ de rayonnement sont dĂ©truits par le rayonnement. Dans la partie intĂ©rieure de la nĂ©buleuse de la TĂȘte de cheval, les grains sont constituĂ©s d'agrĂ©gats, comme attendu dans les rĂ©gions Ă haute densitĂ©
PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
International audienceThe JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate
PDRs4All. II. JWST's NIR and MIR imaging view of the Orion Nebula
International audienceContext. The James Webb Space Telescope (JWST) has captured the most detailed and sharpest infrared (IR) images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR).Aims. We investigate the fundamental interaction of far-ultraviolet (FUV) photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments.Methods. We utilized NIRCam and MIRI to obtain sub-arcsecond images over ~150âł and 42âł in key gas phase lines (e.g., Pa α, Br α, [FeII] 1.64 ”m, H2 1â0 S(1) 2.12 ”m, 0â0 S(9) 4.69 ”m), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3â3.4 ”m, 7.7, and 11.3 ”m), dust emission, and scattered light. Their emission are powerful tracers of the IF and DF, FUV radiation field and density distribution. Using NIRSpec observations the fractional contributions of lines, AIBs, and continuum emission to our NIRCam images were estimated. A very good agreement is found for the distribution and intensity of lines and AIBs between the NIRCam and NIRSpec observations.Results. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of ~0.1â1âł (~0.0002â0.002 pc or ~40â400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. The spatial distribution of the AIBs reveals that the PDR edge is steep and is followed by an extensive warm atomic layer up to the DF with multiple ridges. A complex, structured, and folded H0/H2 DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar as our observations show that a 3D âterracedâ geometry is required to explain the JWST observations. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate.Conclusions. This study offers an unprecedented dataset to benchmark and transform PDR physico-chemical and dynamical models for the JWST era. A fundamental step forward in our understanding of the interaction of FUV photons with molecular clouds and the role of FUV irradiation along the star formation sequence is provided
A far-ultravioletâdriven photoevaporation flow observed in a protoplanetary disk
International audienceMost low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk
PDRs4All VIII: Mid-IR emission line inventory of the Orion Bar
International audienceMid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations
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 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 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 m AIB emission from class B in the molecular PDR to class A 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'
PDRs4All VIII: Mid-IR emission line inventory of the Orion Bar
International audienceMid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations