Browsing by Author "Takashi Onaka"

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C-H Stretch Vibrational Modes: Tracers of Interstellar PAH Geometries?
(American Chemical Society, 2023) Akant Vats; Amit Pathak; Takashi Onaka; Itsuki Sakon; Izumi Endo
Polycyclic aromatic hydrocarbon (PAH) molecules have long been adjudged as carriers of the frequently detected interstellar emission features in the 3-20 μm region. In the present work, PAHs with straight edges having solo-duo (PAHD) and solo-duo-trio (PAHT) C-H modes along with PAHs with irregular edges (PAHI) have been studied theoretically to understand the effect of molecular geometry on the interstellar C-H stretch vibrations at 3.3 μm. The C-H out-of-plane bending vibrations at 11.2 and 12.7 μm are also included for completeness. Using the NASA Ames PAH IR Spectroscopic Database, the mid-infrared spectra have been studied for 125 PAH molecules of varying molecular geometries, sizes, charge states, and symmetries. Results show that the individual solo, duo, and trio C-H stretches follow an order in the peak wavelength (λ3.3 (solo) > λ3.3 (duo) > λ3.3 (trio)) and intensity (I3.3 (solo) < I3.3 (duo) < I3.3 (trio)). If only PAHD’s are considered, the contribution of each charge state is required to account for the observed peak wavelength of the 3.3 μm band, or if only neutrals are contributors, PAHD and PAHT neutrals can explain the 3.3 μm band variations. The observed emission at 11.2 and 12.7 μm is found to match effectively with PAHD with increasing size, and the 11.2 μm band is present at longer wavelengths for PAHT contributing to the red wing. When the solo to duo hydrogen ratio is nearly equal to or greater than 1.0, PAHD neutrals yield better 3.3 μm peak positions. The ratio has a lower limit of 0.8 for the 11.2 μm band and converges at 1.5, indicating a size range of PAHD neutrals with 80 to larger numbers of carbon atoms. The present work examines the presence of solo, duo, and trio modes in the C-H stretching band, which must be taken into consideration when interpreting accurate data from James Webb Space Telescope (JWST) to further explain the observed variations in the interstellar 3.3 μm. © 2023 American Chemical Society.
DFT Study on Interstellar PAH Molecules with Aliphatic Side Groups
(Institute of Physics Publishing, 2020) Mridusmita Buragohain; Amit Pathak; Itsuki Sakon; Takashi Onaka
Polycyclic aromatic hydrocarbon (PAH) molecules have been long adjudged to contribute to the frequently detected distinct emission features at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with weaker and blended features distributed in the 3-20 μm region. The comparatively weaker 3.4 μm emission feature has been attributed to have an aliphatic origin as carrier. PAH with an aliphatic functional group attached to it is one of the proposed potential candidate carriers for the 3.4 μm emission band, however, the assignment of carrier is still enigmatic. In this work, we employ density functional theory calculation on a symmetric and compact PAH molecule; coronene (C24H12) with aliphatic side group to investigate any spectral similarities with observed features at 3-4 μm. The side groups considered in this study are-H (hydrogenated),-CH3 (methyl),-CH2-CH3 (ethyl), and-CH=CH2 (vinyl) functional groups. Considering the possible presence of deuterium (D) in PAHs, we also include D in the aliphatic side group to study the spectral behavior. We present a detailed analysis of the IR spectra of these molecules and discuss possible astrophysical implications. © 2020. The American Astronomical Society. All rights reserved.
Investigating C−D out-of-plane vibrational modes in PAHs as a tool to study interstellar deuterium-containing PAHs
(Oxford University Press, 2025) Mridusmita Buragohain; Takashi Onaka; Amit Pathak; Akant Vats; Itsuki Sakon
Previous as well as recent observations by ISO, Spitzer, AKARI, SOFIA, JWST etc. have revealed various characteristics of midinfrared emission bands between 3 and 20 μm. Subsequently,severalforms of organicsincluding polycylic aromatic hydrocarbons (PAHs)/PAH-like molecules are proposed as carriers for these bands. Deuterated PAH (PAD) is one such substituted PAH, which is proposed as a potential candidate carrier for weak emission bands at 4.4 and 4.65 μm, detected towards few astronomical targets and are characteristics of aromatic and aliphatic C−D stretching modes in a PAD molecule, respectively. However, the 4.4 μm band is not widely detected. In order to validate PADs as carriers for mid-infrared emission bands, an additional alternative tool is crucial. If PAHs are deuterated, they should also possess an inherent signature from the C−D out-of-plane (C−Doop) vibrations, which are at the longer wavelength side. In this report, features due to C−Doop modes in PAHs bearing a single to multiple deuterium atoms are reported by performing quantum-chemical calculations. This paper reports that some of the C−Doop vibrations appear at the 14–19 μm range. Also, the strength of C−Doop modes is not proportional to the D/H ratio in PAHs. In addition, a moderate change in the spectra of deuterated PAHs is observed from that of the undeuterated counterparts, as deuteration would alternate the adjacency class of the C-H bonds and the mass distribution of the molecule. We discuss the efficiency and usefulness of these bands to constrain the form of PAHs emitting mid-infrared emission bands. © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
Laboratory Measurements of Stretching Band Strengths of Deuterated Quenched Carbonaceous Composites
(Institute of Physics, 2022) Tamami Mori; Takashi Onaka; Itsuki Sakon; Mridusmita Buragohain; Naoto Takahata; Yuji Sano; Amit Pathak
The observed large variation in the abundance of deuterium (D) in the interstellar medium suggests that a significant fraction of D may be depleted into polycyclic aromatic hydrocarbons (PAHs). Signatures of the deuteration of PAHs are expected to appear most clearly through the C-D stretching modes at 4.4-4.7 μm, whose strengths in emission spectra relative to those of the C-H stretching modes at 3.3-3.5 μm provide the relative abundance of D to hydrogen (H) in PAHs, once we have accurate relative band strengths of both stretching modes. We report experimental results of the band strengths of the C-D stretching modes relative to the C-H stretching modes. We employ a laboratory analog of interstellar carbonaceous dust, Quenched Carbonaceous Composite (QCC), and synthesize deuterated QCC (D-QCC) by replacing the QCC starting gas of CH4 with mixtures of CH4 and CD4 with various ratios. Infrared spectra of D-QCC are taken to estimate the relative band strengths of the stretching modes, while the D/H ratios in the D-QCC samples are measured with a nanoscale secondary ion mass spectrometer. We obtain relative strengths of aromatic and aliphatic C-D to C-H stretches as 0.56 ± 0.04 and 0.38 ± 0.01 per D/H, respectively. The ratio for the aromatic stretches is in good agreement with the results of theoretical calculations, while that for the aliphatic stretches is smaller than that for the aromatic stretches. The present results do not significantly change the D/H ratios in interstellar PAHs that have previously been estimated from observed spectra. © 2022. The Author(s). Published by the American Astronomical Society.
PDRs4All II. JWST’s NIR and MIR imaging view of the Orion Nebula
(EDP Sciences, 2024) Emilie Habart; Els Peeters; Olivier Berné; Boris Trahin; Amélie Canin; Ryan Chown; Ameek Sidhu; Dries Van De Putte; Felipe Alarcón; Ilane Schroetter; Emmanuel Dartois; Sílvia Vicente; Alain Abergel; Edwin A. Bergin; Jeronimo Bernard-Salas; Christiaan Boersma; Emeric Bron; Jan Cami; Sara Cuadrado; Daniel Dicken; Meriem Elyajouri; Asunción Fuente; Javier R. Goicoechea; Karl D. Gordon; Lina Issa; Christine Joblin; Olga Kannavou; Baria Khan; Ozan Lacinbala; David Languignon; Romane Le Gal; Alexandros Maragkoudakis; Raphael Meshaka; Yoko Okada; Takashi Onaka; Sofia Pasquini; Marc W. Pound; Massimo Robberto; Markus Röllig; Bethany Schefter; Thiébaut Schirmer; Benoit Tabone; Alexander G.G.M. Tielens; Mark G. Wolfire; Marion Zannese; Nathalie Ysard; Marc-Antoine Miville-Deschenes; Isabel Aleman; Louis Allamandola; Rebecca Auchettl; Giuseppe Antonio Baratta; Salma Bejaoui; Partha P. Bera; John H. Black; Francois Boulanger; Jordy Bouwman; Bernhard Brandl; Philippe Brechignac; Sandra Brünken; Mridusmita Buragohain; Andrew Burkhardt; Alessandra Candian; Stéphanie Cazaux; Jose Cernicharo; Marin Chabot; Shubhadip Chakraborty; Jason Champion; Sean W.J. Colgan; Ilsa R. Cooke; Audrey Coutens; Nick L.J. Cox; Karine Demyk; Jennifer Donovan Meyer; Sacha Foschino; Pedro García-Lario; Lisseth Gavilan; Maryvonne Gerin; Carl A. Gottlieb; Pierre Guillard; Antoine Gusdorf; Patrick Hartigan; Jinhua He; Eric Herbst; Liv Hornekaer; Cornelia Jäger; Eduardo Janot-Pacheco; Michael Kaufman; Francisca Kemper; Sarah Kendrew; Maria S. Kirsanova; Pamela Klaassen; Sun Kwok; Álvaro Labiano; Thomas S.-Y. Lai; Timothy J. Lee; Bertrand Lefloch; Franck Le Petit; Aigen Li; Hendrik Linz; Cameron J. Mackie; Suzanne C. Madden; Joëlle Mascetti; Brett A. McGuire; Pablo Merino; Elisabetta R. Micelotta; Karl Misselt; Jon A. Morse; Giacomo Mulas; Naslim Neelamkodan; Ryou Ohsawa; Alain Omont; Roberta Paladini; Maria Elisabetta Palumbo; Amit Pathak; Yvonne J. Pendleton; Annemieke Petrignani; Thomas Pino; Elena Puga; Naseem Rangwala; Mathias Rapacioli; Alessandra Ricca; Julia Roman-Duval; Joseph Roser; Evelyne Roueff; Gaël Rouillé; Farid Salama; Dinalva A. Sales; Karin Sandstrom; Peter Sarre; Ella Sciamma-O’Brien; Kris Sellgren; Sachindev S. Shenoy; David Teyssier; Richard D. Thomas; Aditya Togi; Laurent Verstraete; Adolf N. Witt; Alwyn Wootten; Henning Zettergren; Yong Zhang; Ziwei E. Zhang; Junfeng Zhen
Context. 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 ∼150′′ and 42′′ in key gas phase lines (e.g., Pa α, Br α, [FeII] 1.64 µm, H2 1–0 S(1) 2.12 µm, 0–0 S(9) 4.69 µm), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3–3.4 µm, 7.7, and 11.3 µm), 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 ∼0.1–1′′ (∼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. 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 “terraced” 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. © The Authors 2024.
PDRs4All VIII. Mid-infrared emission line inventory of the Orion Bar
(EDP Sciences, 2024) Dries Van De Putte; Raphael Meshaka; Boris Trahin; Emilie Habart; Els Peeters; Olivier Berné; Felipe Alarcón; Amélie Canin; Ryan Chown; Ilane Schroetter; Ameek Sidhu; Christiaan Boersma; Emeric Bron; Emmanuel Dartois; Javier R. Goicoechea; Karl D. Gordon; Takashi Onaka; Alexander G.G.M. Tielens; Laurent Verstraete; Mark G. Wolfire; Alain Abergel; Edwin A. Bergin; Jeronimo Bernard-Salas; Jan Cami; Sara Cuadrado; Daniel Dicken; Meriem Elyajouri; Asunción Fuente; Christine Joblin; Baria Khan; Ozan Lacinbala; David Languignon; Romane Le Gal; Alexandros Maragkoudakis; Yoko Okada; Sofia Pasquini; Marc W. Pound; Massimo Robberto; Markus Röllig; Bethany Schefter; Thiébaut Schirmer; Benoit Tabone; Sílvia Vicente; Marion Zannese; Sean W.J. Colgan; Jinhua He; Gaël Rouillé; Aditya Togi; Isabel Aleman; Rebecca Auchettl; Giuseppe Antonio Baratta; Salma Bejaoui; Partha P. Bera; John H. Black; Francois Boulanger; Jordy Bouwman; Bernhard Brandl; Philippe Brechignac; Sandra Brünken; Mridusmita Buragohain; Andrew Burkhardt; Alessandra Candian; Stéphanie Cazaux; Jose Cernicharo; Marin Chabot; Shubhadip Chakraborty; Jason Champion; Ilsa R. Cooke; Audrey Coutens; Nick L.J. Cox; Karine Demyk; Jennifer Donovan Meyer; Sacha Foschino; Pedro García-Lario; Maryvonne Gerin; Carl A. Gottlieb; Pierre Guillard; Antoine Gusdorf; Patrick Hartigan; Eric Herbst; Liv Hornekaer; Lina Issa; Cornelia Jäger; Eduardo Janot-Pacheco; Olga Kannavou; Michael Kaufman; Francisca Kemper; Sarah Kendrew; Maria S. Kirsanova; Pamela Klaassen; Sun Kwok; Álvaro Labiano; Thomas S.-Y. Lai; Bertrand Le Floch; Franck Le Petit; Aigen Li; Hendrik Linz; Cameron J. Mackie; Suzanne C. Madden; Joëlle Mascetti; Brett A. McGuire; Pablo Merino; Elisabetta R. Micelotta; Jon A. Morse; Giacomo Mulas; Naslim Neelamkodan; Ryou Ohsawa; Alain Omont; Roberta Paladini; Maria Elisabetta Palumbo; Amit Pathak; Yvonne J. Pendleton; Annemieke Petrignani; Thomas Pino; Elena Puga; Naseem Rangwala; Mathias Rapacioli; Jeonghee Rho; Alessandra Ricca; Julia Roman-Duval; Joseph Roser; Evelyne Roueff; Farid Salama; Dinalva A. Sales; Karin Sandstrom; Peter Sarre; Ella Sciamma-O’Brien; Kris Sellgren; Sachindev S. Shenoy; David Teyssier; Richard D. Thomas; Adolf N. Witt; Alwyn Wootten; Nathalie Ysard; Henning Zettergren; Yong Zhang; Ziwei E. Zhang; Junfeng Zhen
Context. Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the “PDRs4All” Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2′′) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the H II region, the ionization front, and multiple dissociation fronts. Aims. We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST. Methods. The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths. Results. We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of H I recombination lines arising from the ionized gas layer bordering the PDR. The H I line ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the Ne III/Ne II, S IV/S III, and Ar III/Ar II ratios trace the conditions in the ionized layer bordering the PDR, while Fe III/Fe II and Ni III/Ni II exhibit a different behavior, as there are significant contributions to Fe II and Ni II from the neutral PDR gas. We observe the pure-rotational H2 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 H2 excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (∼700 K) component representative of an average gas temperature, and one nonthermal component (∼2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S(6) to S(8) lines. © The Authors 2024.
PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars
(Institute of Physics, 2022) Olivier Berné; Émilie Habart; Els Peeters; Alain Abergel; Edwin A. Bergin; Jeronimo Bernard-Salas; Emeric Bron; Jan Cami; Emmanuel Dartois; Asunción Fuente; Javier R. Goicoechea; Karl D. Gordon; Yoko Okada; Takashi Onaka; Massimo Robberto; Markus Röllig; Alexander G. G. M. Tielens; Sílvia Vicente; Mark G. Wolfire; Felipe Alarcón; C. Boersma; Amélie Canin; Ryan Chown; Daniel Dicken; David Languignon; Romane Le Gal; Marc W. Pound; Boris Trahin; Thomas Simmer; Ameek Sidhu; Dries Van De Putte; Sara Cuadrado; Claire Guilloteau; Alexandros Maragkoudakis; Bethany R. Schefter; Thiébaut Schirmer; Stéphanie Cazaux; Isabel Aleman; Louis Allamandola; Rebecca Auchettl; Giuseppe Antonio Baratta; Salma Bejaoui; Partha P. Bera; Goranka Bilalbegović; John H. Black; Francois Boulanger; Jordy Bouwman; Bernhard Brandl; Philippe Brechignac; Sandra Brünken; Andrew Burkhardt; Alessandra Candian; Jose Cernicharo; Marin Chabot; Shubhadip Chakraborty; Jason Champion; Sean W. J. Colgan; Ilsa R. Cooke; Audrey Coutens; Nick L. J. Cox; Karine Demyk; Jennifer Donovan Meyer; Cécile Engrand; Sacha Foschino; Pedro García-Lario; Lisseth Gavilan; Maryvonne Gerin; Marie Godard; Carl A. Gottlieb; Pierre Guillard; Antoine Gusdorf; Patrick Hartigan; Jinhua He; Eric Herbst; Liv Hornekaer; Cornelia Jäger; Eduardo Janot-Pacheco; Christine Joblin; Michael Kaufman; Francisca Kemper; Sarah Kendrew; Maria S. Kirsanova; Pamela Klaassen; Collin Knight; Sun Kwok; Álvaro Labiano; Thomas S.-Y. Lai; Timothy J. Lee; Bertrand Lefloch; Franck Le Petit; Aigen Li; Hendrik Linz; Cameron J. MacKie; Suzanne C. Madden; Joëlle Mascetti; Brett A. McGuire; Pablo Merino; Elisabetta R. Micelotta; Karl Misselt; Jon A. Morse; Giacomo Mulas; Naslim Neelamkodan; Ryou Ohsawa; Alain Omont; Roberta Paladini; Maria Elisabetta Palumbo; Amit Pathak; Yvonne J. Pendleton; Annemieke Petrignani; Thomas Pino; Elena Puga; Naseem Rangwala; Mathias Rapacioli; Alessandra Ricca; Julia Roman-Duval; Joseph Roser; Evelyne Roueff; Gaël Rouillé; Farid Salama; Dinalva A. Sales; Karin Sandstrom; Peter Sarre; Ella Sciamma-O'brien; Kris Sellgren; Matthew J. Shannon; Sachindev S. Shenoy; David Teyssier; Richard D. Thomas; Aditya Togi; Laurent Verstraete; Adolf N. Witt; Alwyn Wootten; Nathalie Ysard; Henning Zettergren; Yong Zhang; Ziwei E. Zhang; Junfeng Zhen
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. © 2022. The Astronomical Society of the Pacific. All rights reserved.
PDRs4All: III. JWST's NIR spectroscopic view of the Orion Bar
(EDP Sciences, 2024) Els Peeters; Emilie Habart; Olivier Berné; Ameek Sidhu; Ryan Chown; Dries Van De Putte; Boris Trahin; Ilane Schroetter; Amélie Canin; Felipe Alarcón; Bethany Schefter; Baria Khan; Sofia Pasquini; Alexander G. G. M. Tielens; Mark G. Wolfire; Emmanuel Dartois; Javier R. Goicoechea; Alexandros Maragkoudakis; Takashi Onaka; Marc W. Pound; Sílvia Vicente; Alain Abergel; Edwin A. Bergin; Jeronimo Bernard-Salas; Christiaan Boersma; Emeric Bron; Jan Cami; Sara Cuadrado; Daniel Dicken; Meriem Elyajouri; Asunción Fuente; Karl D. Gordon; Lina Issa; Christine Joblin; Olga Kannavou; Ozan Lacinbala; David Languignon; Romane Le Gal; Raphael Meshaka; Yoko Okada; Massimo Robberto; Markus Röllig; Thiébaut Schirmer; Benoit Tabone; Marion Zannese; Isabel Aleman; Louis Allamandola; Rebecca Auchettl; Giuseppe Antonio Baratta; Salma Bejaoui; Partha P. Bera; John H. Black; Francois Boulanger; Jordy Bouwman; Bernhard Brandl; Philippe Brechignac; Sandra Brünken; Mridusmita Buragohain; Andrew Burkhardt; Alessandra Candian; Stéphanie Cazaux; Jose Cernicharo; Marin Chabot; Shubhadip Chakraborty; Jason Champion; Sean W. J. Colgan; Ilsa R. Cooke; Audrey Coutens; Nick L. J. Cox; Karine Demyk; Jennifer Donovan Meyer; Sacha Foschino; Pedro García-Lario; Maryvonne Gerin; Carl A. Gottlieb; Pierre Guillard; Antoine Gusdorf; Patrick Hartigan; Jinhua He; Eric Herbst; Liv Hornekaer; Cornelia Jäger; Eduardo Janot-Pacheco; Michael Kaufman; Sarah Kendrew; Maria S. Kirsanova; Pamela Klaassen; Sun Kwok; Álvaro Labiano; Thomas S.-Y. Lai; Timothy J. Lee; Bertrand Lefloch; Franck Le Petit; Aigen Li; Hendrik Linz; Cameron J. MacKie; Suzanne C. Madden; Joëlle Mascetti; Brett A. McGuire; Pablo Merino; Elisabetta R. Micelotta; Karl Misselt; Jon A. Morse; Giacomo Mulas; Naslim Neelamkodan; Ryou Ohsawa; Roberta Paladini; Maria Elisabetta Palumbo; Amit Pathak; Yvonne J. Pendleton; Annemieke Petrignani; Thomas Pino; Elena Puga; Naseem Rangwala; Mathias Rapacioli; Alessandra Ricca; Julia Roman-Duval; Joseph Roser; Evelyne Roueff; Gaël Rouillé; Farid Salama; Dinalva A. Sales; Karin Sandstrom; Peter Sarre; Ella Sciamma-O'Brien; Kris Sellgren; Sachindev S. Shenoy; David Teyssier; Richard D. Thomas; Aditya Togi; Laurent Verstraete; Adolf N. Witt; Alwyn Wootten; Nathalie Ysard; Henning Zettergren; Yong Zhang; Ziwei E. Zhang; Junfeng Zhen
Context. JWST has taken the sharpest and most sensitive infrared (IR) spectral imaging observations ever of the Orion Bar photodis-sociation region (PDR), which is part of the nearest massive star-forming region the Orion Nebula, and often considered to be the 'prototypical'strongly illuminated PDR. Aims. We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the H II region to the atomic PDR -crossing the ionisation front (IF) -, and the subsequent transition to the molecular PDR -crossing the dissociation front (DF). Given the prevalence of PDRs in the interstellar medium and their dominant contribution to IR radiation, understanding the response of the PDR gas to far-ultraviolet (FUV) photons and the associated physical and chemical processes is fundamental to our understanding of star and planet formation and for the interpretation of any unresolved PDR as seen by JWST. Methods. We used high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science programme. We constructed a 3″ × 25″ spatio-spectral mosaic covering 0.97-5.27 μm at a spectral resolution R of ~2700 and an angular resolution of 0.075″-0.173″. To study the properties of key regions captured in this mosaic, we extracted five template spectra in apertures centred on the three H2 dissociation fronts, the atomic PDR, and the H II region. This wealth of detailed spatial-spectral information was analysed in terms of variations in the physical conditions-incident UV field, density, and temperature -of the PDR gas. Results. The NIRSpec data reveal a forest of lines including, but not limited to, He I, H I, and C I recombination lines; ionic lines (e.g. Fe III and Fe II); O I and N I fluorescence lines; aromatic infrared bands (AIBs, including aromatic CH, aliphatic CH, and their CD counterparts); pure rotational and ro-vibrational lines from H2; and ro-vibrational lines from HD, CO, and CH+, with most of them having been detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. In addition, we observed numerous smaller-scale structures whose typical size decreases with distance from θ1 Ori C and IR lines from C I, if solely arising from radiative recombination and cascade, reveal very high gas temperatures (a few 1000 K) consistent with the hot irradiated surface of small-scale dense clumps inside the PDR. The morphology of the Bar, in particular that of the H2 lines, reveals multiple prominent filaments that exhibit different characteristics. This leaves the impression of a 'terraced'transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. We attribute the different characteristics of the H2 filaments to their varying depth into the PDR and, in some cases, not reaching the C+/C/CO transition. These observations thus reveal what local conditions are required to drive the physical and chemical processes needed to explain the different characteristics of the DFs and the photochemical evolution of the AIB carriers. Conclusions. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star and planet formation as well as galaxy evolution. © 2024 EDP Sciences. All rights reserved.
PDRs4All: IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
(EDP Sciences, 2024) Ryan Chown; Ameek Sidhu; Els Peeters; Alexander G. G. M. Tielens; Jan Cami; Olivier Berné; Emilie Habart; Felipe Alarcón; Amélie Canin; Ilane Schroetter; Boris Trahin; Dries Van De Putte; Alain Abergel; Edwin A. Bergin; Jeronimo Bernard-Salas; Christiaan Boersma; Emeric Bron; Sara Cuadrado; Emmanuel Dartois; Daniel Dicken; Meriem El-Yajouri; Asunción Fuente; Javier R. Goicoechea; Karl D. Gordon; Lina Issa; Christine Joblin; Olga Kannavou; Baria Khan; Ozan Lacinbala; David Languignon; Romane Le Gal; Alexandros Maragkoudakis; Raphael Meshaka; Yoko Okada; Takashi Onaka; Sofia Pasquini; Marc W. Pound; Massimo Robberto; Markus Röllig; Bethany Schefter; Thiébaut Schirmer; Sílvia Vicente; Mark G. Wolfire; Marion Zannese; Isabel Aleman; Louis Allamandola; Rebecca Auchettl; Giuseppe Antonio Baratta; Salma Bejaoui; Partha P. Bera; John H. Black; François Boulanger; Jordy Bouwman; Bernhard Brandl; Philippe Brechignac; Sandra Brünken; Mridusmita Buragohain; Andrew Burkhardt; Alessandra Candian; Stéphanie Cazaux; Jose Cernicharo; Marin Chabot; Shubhadip Chakraborty; Jason Champion; Sean W. J. Colgan; Ilsa R. Cooke; Audrey Coutens; Nick L. J. Cox; Karine Demyk; Jennifer Donovan Meyer; Sacha Foschino; Pedro García-Lario; Lisseth Gavilan; Maryvonne Gerin; Carl A. Gottlieb; Pierre Guillard; Antoine Gusdorf; Patrick Hartigan; Jinhua He; Eric Herbst; Liv Hornekaer; Cornelia Jäger; Eduardo Janot-Pacheco; Michael Kaufman; Francisca Kemper; Sarah Kendrew; Maria S. Kirsanova; Pamela Klaassen; Sun Kwok; Álvaro Labiano; Thomas S.-Y. Lai; Timothy J. Lee; Bertrand Lefloch; Franck Le Petit; Aigen Li; Hendrik Linz; Cameron J. Mackie; Suzanne C. Madden; Joëlle Mascetti; Brett A. Mcguire; Pablo Merino; Elisabetta R. Micelotta; Karl Misselt; Jon A. Morse; Giacomo Mulas; Naslim Neelamkodan; Ryou Ohsawa; Alain Omont; Roberta Paladini; Maria Elisabetta Palumbo; Amit Pathak; Yvonne J. Pendleton; Annemieke Petrignani; Thomas Pino; Elena Puga; Naseem Rangwala; Mathias Rapacioli; Alessandra Ricca; Julia Roman-Duval; Joseph Roser; Evelyne Roueff; Gaël Rouillé; Farid Salama; Dinalva A. Sales; Karin Sandstrom; Peter Sarre; Ella Sciamma-O'brien; Kris Sellgren; Sachindev S. Shenoy; David Teyssier; Richard D. Thomas; Aditya Togi; Laurent Verstraete; Adolf N. Witt; Alwyn Wootten; Henning Zettergren; Yong Zhang; Ziwei E. Zhang; Junfeng Zhen
Context. 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 µm. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. These high-quality data allow for an unprecedentedly detailed view of AIBs. Aims. 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 (i.e. the three H2 dissociation fronts), the atomic PDR, and the H II region. Methods. We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extracted five template spectra to represent the morphology and environment of the Orion Bar PDR. We investigated and characterised the AIBs in these template spectra. We describe the variations among them here. Results. 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. The Orion Bar spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 µm with well-defined profiles. In addition, the spectra display a wealth of weaker features and sub-components. The widths of many AIBs show clear and systematic variations, being narrowest in the atomic PDR template, but showing a clear broadening in the H II region template while the broadest bands are found in the three dissociation front templates. In addition, the relative strengths of AIB (sub-)components vary among the template spectra as well. All AIB profiles are characteristic of class A sources as designated by Peeters (2022, A&A, 390, 1089), except for the 11.2 µm AIB profile deep in the molecular zone, which belongs to class B11.2. Furthermore, the observations show that the sub-components that contribute to the 5.75, 7.7, and 11.2 µm AIBs become much weaker in the PDR surface layers. We attribute this to the presence of small, more labile carriers in the deeper PDR layers that are photolysed away in the harsh radiation field near the surface. The 3.3/11.2 AIB intensity ratio decreases by about 40% between the dissociation fronts and the H II region, indicating a shift in the polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs in the PDR surface layers, also likely due to the effects of photochemistry. The observed broadening of the bands in the molecular PDR is consistent with an enhanced importance of smaller PAHs since smaller PAHs attain a higher internal excitation energy at a fixed photon energy. Conclusions. Spectral-imaging observations of the Orion Bar using JWST yield key insights into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 µm AIB emission from class B11.2 in the molecular PDR to class A11.2 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’. © The Authors 2024.
Theoretical Rotational and Vibrational Investigation of Oxygen-Functionalized Interstellar PAHs
(Oxford University Press, 2025) Shivani Mishra; Akant Vats; Satyam Srivastav; Amit Pathak; Peter J. Sarre; Takashi Onaka; Itsuki Sakon
Oxygen-functionalized polycyclic aromatic hydrocarbons (OPAHs) with OH, CHO, and CO side groups can form in the interstellar medium (ISM) mainly through the UV irradiation of PAHs in water ice. Inspired by the detection of nitrogen-containing PAHs in the ISM, this study uses highly accurate computational techniques to investigate the rotational and vibrational spectra of oxygen-functionalized pyrene derivatives (Py-OH, Py-CHO, Py-HO, and Py-O2) for comparison with experiments that could aid in their future detection. All four OPAHs exhibit strong dipole moments and rotational lines, observable in denser ISM regions near 12 GHz, 10.2 GHz, 12.6 GHz, and 9.6 GHz, respectively. The strongest IR absorption features are identified at 1179.9 cm−1 (8.47 μm) and 1385.0 cm−1 (7.22 μm) for Py-OH, 1733.4 cm−1 (5.77 μm) for Py-CHO, 1747.7 cm−1 (5.72 μm) for Py-HO, and 1613.0 cm−1 (6.20 μm) for Py-O2. The IR features of Py-OH and Py-O2 exhibit peaks in the CO stretching region around 6.0 μm, while those of Py-CHO and Py-HO are blue-shifted due to anharmonicity from the additional CH bond. This suggests PAHs with CO group and no additional peripheral CH bond better explain the observed 6.0 μm PAH emission. However, to explain the observed PAH emission bands with the OPAHs, a fully emission-cascade treatment is required in the anharmonic IR spectra. The accurate spectral data presented here are crucial for experimental classification and potential interstellar observations. © 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
Theoretical study of infrared spectra of interstellar PAH molecules with N, NH, and NH2incorporation
(Oxford University Press, 2022) Akant Vats; Amit Pathak; Takashi Onaka; Mridusmita Buragohain; Itsuki Sakon; Izumi Endo
This work presents theoretical calculations of infrared spectra of nitrogen (N)-containing polycyclic aromatic hydrocarbon (PAH) molecules with the incorporation of N, NH, and NH2 using density functional theory (DFT). The properties of their vibrational modes in 2-15 μm are investigated in relation to the Unidentified Infrared (UIR) bands. It is found that neutral PAHs, when incorporated with NH2 and N (at inner positions), produce intense infrared bands at 6.2, 7.7, and 8.6 μm that have been normally attributed to ionized PAHs so far. The present results suggest that strong bands at 6.2 and 11.2 μm can arise from the same charge state of some N-containing PAHs, arguing that there might be some N-abundant astronomical regions where the 6.2 to 11.2 μm band ratio is not a direct indicator of the PAHs' ionization. PAHs with NH2 and N inside the carbon structure show the UIR band features characteristic to star-forming regions as well as reflection nebulae (Class A), whereas PAHs with N at the periphery have similar spectra to the UIR bands seen in planetary nebulae and post-AGB stars (Class B). The presence of N atoms at the periphery of a PAH may attract H or H+ to form N-H and N-H2 bonds, exhibiting features near 2.9-3.0 μm, which are not yet observationally detected. The absence of such features in the observations constrains the contribution of NH and NH2 substituted PAHs that could be better tested with concentrated observations in this range. However, PAHs with N without H either at the periphery or inside the carbon structure do not have the abundance constraint due to the absence of 2.9-3.0 μm features and are relevant in terms of positions of the UIR bands. Extensive theoretical and experimental studies are required to obtain deeper insight. © 2021 The Author(s).