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Goicoechea JR, Cuadrado S, Le Petit F. Multi-line Observations, Models, and Data Needed to Understand the Nature of UV-irradiated Interstellar Matter. EPJ WEB OF CONFERENCES 2022. [DOI: 10.1051/epjconf/202226500003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Far-ultraviolet photons from OB-type massive stars regulate the heating, ionization, and chemistry of much of the neutral interstellar gas in star-forming galaxies. The interaction of FUV radiation and interstellar matter takes place in environments broadly known as photodissociation regions (PDRs). PDR line diagnostics are the smoking gun of the radiative feedback from massive stars. Improving our understanding of stellar feedback in the ISM requires quantifying the energy budget, gas dynamics, and chemical composition of PDR environments. This goal demands astronomical instrumentation able to deliver multi-line spectroscopic images of the ISM (of the Milky Way and nearby galaxies). It also requires interdisciplinary collaborations to obtain the rate coefficients and cross sections of the many microphysical processes that occur in the ISM and that are included in models such as the Meudon PDR code.
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Linz H, Beuther H, Gerin M, Goicoechea JR, Helmich F, Krause O, Liu Y, Molinari S, Ossenkopf-Okada V, Pineda J, Sauvage M, Schinnerer E, van der Tak F, Wiedner M, Amiaux J, Bhatia D, Buinhas L, Durand G, Förstner R, Graf U, Lezius M. Bringing high spatial resolution to the far-infrared: A giant leap for astrophysics. EXPERIMENTAL ASTRONOMY 2021; 51:661-697. [PMID: 34744305 PMCID: PMC8536553 DOI: 10.1007/s10686-021-09719-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 03/02/2021] [Indexed: 06/13/2023]
Abstract
The far-infrared (FIR) regime is one of the wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist. None of the medium-term satellite projects like SPICA, Millimetron, or the Origins Space Telescope will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO), light hydrides, and especially from water lines would open the door for transformative science. A main theme will be to trace the role of water in proto-planetary discs, to observationally advance our understanding of the planet formation process and, intimately related to that, the pathways to habitable planets and the emergence of life. Furthermore, key observations will zoom into the physics and chemistry of the star-formation process in our own Galaxy, as well as in external galaxies. The FIR provides unique tools to investigate in particular the energetics of heating, cooling, and shocks. The velocity-resolved data in these tracers will reveal the detailed dynamics engrained in these processes in a spatially resolved fashion, and will deliver the perfect synergy with ground-based molecular line data for the colder dense gas.
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Affiliation(s)
- Hendrik Linz
- Max-Planck-Institut für Astronomie, Heidelberg, Germany
| | | | - Maryvonne Gerin
- Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, Paris, France
| | | | - Frank Helmich
- SRON Netherlands Institute for Space Research, Groningen, Netherlands
| | - Oliver Krause
- Max-Planck-Institut für Astronomie, Heidelberg, Germany
| | - Yao Liu
- Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
- Present Address: Purple Mountain Observatory, Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing, China
| | - Sergio Molinari
- Istituto di Astrofisica e Planetologia Spaziale, INAF, Rome, Italy
| | | | - Jorge Pineda
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
| | - Marc Sauvage
- AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | | | - Floris van der Tak
- SRON, Kapteyn Astronomical Institute, University of Groningen, Groningen, Netherlands
| | - Martina Wiedner
- Observatoire de Paris, PSL university, Sorbonne Université, CNRS, LERMA, Paris, France
| | - Jerome Amiaux
- AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Divya Bhatia
- Institut für Flugführung, TU Braunschweig, Braunschweig, Germany
- Present Address: Independent Spacecraft AOCS/GNC Research Engineer, Braunschweig, Germany
| | - Luisa Buinhas
- Universität der Bundeswehr München, Neubiberg, Germany
- Present Address: Space Systems Engineer, Vyoma GmbH, Darmstadt, Germany
| | - Gilles Durand
- AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | | | - Urs Graf
- 1. Physikalisches Institut, Universität zu Köln, Cologne, Germany
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Pabst CHM, Goicoechea JR, Teyssier D, Berné O, Higgins RD, Chambers ET, Kabanovic S, Güsten R, Stutzki J, Tielens AGGM. Expanding bubbles in Orion A: [C II] observations of M42, M43, and NGC 1977. ASTRONOMY AND ASTROPHYSICS 2020; 639:A2. [PMID: 33173232 PMCID: PMC7116338 DOI: 10.1051/0004-6361/202037560] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
CONTEXT The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies. AIMS We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [C II] 158μm fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [C II] emission from the Orion Nebula complex at a spatial resolution of 16″ and high spectral resolution of 0.2kms-1, covering the entire Orion Nebula (M42) plus M43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them. METHODS We use [C II] 158μm line observations over an area of 1.2deg2 in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA. RESULTS The bubble blown by the O7V star θ 1 Ori C in the Orion Nebula expands rapidly, at 13kms-1. Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6kms-1. Comparison with analytical models for the pressure-driven expansion of H II regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5kms-1, likely due to the over-pressurized ionized gas as in the case of M43. We derive an age of 0.4 Myr for this structure. CONCLUSIONS We conclude that the bubble of the Orion Nebula is driven by the mechanical energy input by the strong stellar wind from θ 1 Ori C, while the bubbles associated with M43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars.
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Affiliation(s)
- C H M Pabst
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, Netherlands
| | - J R Goicoechea
- Instituto de Fisica Fundamental, CSIC, Calle Serrano 121-123, 28006 Madrid, Spain
| | - D Teyssier
- Telespazio Vega UK Ltd. for ESA/ESAC, Urbanizacion Villafranca del Castillo, 28691 Madrid, Spain
| | - O Berné
- IRAP, Université de Toulouse, CNRS, CNES, UPS, 9 Av. colonel Roche, 31028 Toulouse Cedex 4, France
| | - R D Higgins
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - E T Chambers
- USRA/SOFIA, NASA Ames Research Center, Mail Stop 232-12, Building N232, P.O. Box 1, Moffett Field, CA 94035-0001, USA
| | - S Kabanovic
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - R Güsten
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
| | - J Stutzki
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - A G G M Tielens
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, Netherlands
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Cuadrado S, Salas P, Goicoechea JR, Cernicharo J, Tielens AGGM, Báez-Rubio A. Direct estimation of electron density in the Orion Bar PDR from mm-wave carbon recombination lines. ASTRONOMY AND ASTROPHYSICS 2019; 625:10.1051/0004-6361/201935556. [PMID: 31186576 PMCID: PMC6558286 DOI: 10.1051/0004-6361/201935556] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
CONTEXT A significant fraction of the molecular gas in star-forming regions is irradiated by stellar UV photons. In these environments, the electron density (n e) plays a critical role in the gas dynamics, chemistry, and collisional excitation of certain molecules. AIMS We determine n e in the prototypical strongly irradiated photodissociation region (PDR), the Orion Bar, from the detection of new millimeter-wave carbon recombination lines (mmCRLs) and existing far-IR [13Cii] hyperfine line observations. METHODS We detect 12 mmCRLs (including α, β, and γ transitions) observed with the IRAM 30m telescope, at ~ 25″ angular resolution, toward the H/H2 dissociation front (DF) of the Bar. We also present a mmCRL emission cut across the PDR. RESULTS These lines trace the C+/C/CO gas transition layer. As the much lower frequency carbon radio recombination lines, mmCRLs arise from neutral PDR gas and not from ionized gas in the adjacent Hii region. This is readily seen from their narrow line profiles (Δv = 2.6 ± 0.4 km s-1) and line peak velocities (ν LSR = +10.7 ± 0.2 km s-1). Optically thin [13Cii] hyperfine lines and molecular lines - emitted close to the DF by trace species such as reactive ions CO+ and HOC+ - show the same line profiles. We use non-LTE excitation models of [13Cii] and mmCRLs and derive n e = 60 - 100 cm-3 and T e = 500 - 600 K toward the DF. CONCLUSIONS The inferred electron densities are high, up to an order of magnitude higher than previously thought. They provide a lower limit to the gas thermal pressure at the PDR edge without using molecular tracers. We obtain P th ≥ (2 - 4)·108 cm-3 K assuming that the electron abundance is equal to or lower than the gas-phase elemental abundance of carbon. Such elevated thermal pressures leave little room for magnetic pressure support and agree with a scenario in which the PDR photoevaporates.
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Affiliation(s)
- S. Cuadrado
- Instituto de Física Fundamental (IFF-CSIC). Calle Serrano
121-123, E28006 Madrid, Spain
| | - P. Salas
- Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA
Leiden, The Netherlands
| | - J. R. Goicoechea
- Instituto de Física Fundamental (IFF-CSIC). Calle Serrano
121-123, E28006 Madrid, Spain
| | - J. Cernicharo
- Instituto de Física Fundamental (IFF-CSIC). Calle Serrano
121-123, E28006 Madrid, Spain
| | - A. G. G. M. Tielens
- Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA
Leiden, The Netherlands
| | - A. Báez-Rubio
- Centro de Astrobiología (CSIC-INTA), Ctra. de Torrejón
a Ajalvir, km 4, E28850 Torrejón de Ardoz, Madrid, Spain
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Goicoechea JR, Santa-Maria MG, Bron E, Teyssier D, Marcelino N, Cernicharo J, Cuadrado S. Molecular tracers of radiative feedback in Orion (OMC-1) Widespread CH + ( J = 1-0), CO (10-9), HCN (6-5), and HCO + (6-5) emission. ASTRONOMY AND ASTROPHYSICS 2019; 622:A91. [PMID: 30820064 PMCID: PMC6390943 DOI: 10.1051/0004-6361/201834409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud and surroundings. It is important to find tracers that help quantifying the stellar feedback processes that take place at different spatial scales. We present ~85 arcmin2 (~1.3 pc2) velocity-resolved maps of several submillimeter molecular lines, taken with Herschel/HIFI, toward the closest high-mass star-forming region, the Orion molecular cloud 1 core (OMC-1). The observed rotational lines include probes of warm and dense molecular gas that are difficult, if not impossible, to detect from ground-based telescopes: CH+ (J = 1-0), CO (J = 10-9), HCO+ (J = 6-5) and HCN (J = 6-5), and CH (N, J =1, 3/2-1, 1/2). These lines trace an extended but thin layer (A V ≃3-6 mag or ~1016 cm) of molecular gas at high thermal pressure, P th = n H · T k ≈ 107 - 109 cm-3 K, associated with the far ultraviolet (FUV) irradiated surface of OMC-1. The intense FUV radiation field, emerging from massive stars in the Trapezium cluster, heats, compresses and photoevaporates the cloud edge. It also triggers the formation of specific reactive molecules such as CH+. We find that the CH+ (J = 1-0) emission spatially correlates with the flux of FUV photons impinging the cloud: G 0 from ~103 to ~105. This correlation is supported by constant-pressure photodissociation region (PDR) models in the parameter space P th/G 0 ≈ [5 · 103 - 8 · 104] cm-3 K where many observed PDRs seem to lie. The CH+ (J = 1-0) emission spatially correlates with the extended infrared emission from vibrationally excited H2 (v ≥ 1), and with that of [C ii] 158 μm and CO J = 10-9, all emerging from FUV-irradiated gas. These correlations link the presence of CH+ to the availability of C+ ions and of FUV-pumped H2 (v ≥ 1) molecules. We conclude that the parsec-scale CH+ emission and narrow-line (Δv ≃ 3 km s-1) mid-J CO emission arises from extended PDR gas and not from fast shocks. PDR line tracers are the smoking gun of the stellar feedback from young massive stars. The PDR cloud surface component in OMC-1, with a mass density of 120-240 M ⊙ pc-2, represents ~5% to ~10% of the total gas mass, however, it dominates the emitted line luminosity; the average CO J = 10-9 surface luminosity in the mapped region being ~35 times brighter than that of CO J = 2-1. These results provide insights into the source of submillimeter CH+ and mid-J CO emission from distant star-forming galaxies.
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Affiliation(s)
- Javier R Goicoechea
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
| | - Miriam G Santa-Maria
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
| | - Emeric Bron
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
| | - David Teyssier
- Telespazio Vega UK Ltd for ESA/ESAC. Urbanización Villafranca del Castillo, Villanueva de la Cañada, E-28692 Madrid, Spain
| | - Nuria Marcelino
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
| | - José Cernicharo
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
| | - Sara Cuadrado
- Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain
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Pabst C, Higgins R, Goicoechea JR, Teyssier D, Berne O, Chambers E, Wolfire M, Suri ST, Guesten R, Stutzki J, Graf UU, Risacher C, Tielens AGGM. Disruption of the Orion molecular core 1 by wind from the massive star θ 1 Orionis C. Nature 2019; 565:618-621. [PMID: 30617315 DOI: 10.1038/s41586-018-0844-1] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 12/05/2018] [Indexed: 11/10/2022]
Abstract
Massive stars inject mechanical and radiative energy into the surrounding environment, which stirs it up, heats the gas, produces cloud and intercloud phases in the interstellar medium, and disrupts molecular clouds (the birth sites of new stars1,2). Stellar winds, supernova explosions and ionization by ultraviolet photons control the lifetimes of molecular clouds3-7. Theoretical studies predict that momentum injection by radiation should dominate that by stellar winds8, but this has been difficult to assess observationally. Velocity-resolved large-scale images in the fine-structure line of ionized carbon ([C II]) provide an observational diagnostic for the radiative energy input and the dynamics of the interstellar medium around massive stars. Here we report observations of a one-square-degree region (about 7 parsecs in diameter) of Orion molecular core 1-the region nearest to Earth that exhibits massive-star formation-at a resolution of 16 arcseconds (0.03 parsecs) in the [C II] line at 1.9 terahertz (158 micrometres). The results reveal that the stellar wind originating from the massive star θ1 Orionis C has swept up the surrounding material to create a 'bubble' roughly four parsecs in diameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per second. This finding demonstrates that the mechanical energy from the stellar wind is converted very efficiently into kinetic energy of the shell and causes more disruption of the Orion molecular core 1 than do photo-ionization and evaporation or future supernova explosions.
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Affiliation(s)
- C Pabst
- Leiden Observatory, Leiden University, Leiden, The Netherlands
| | - R Higgins
- I. Physikalisches Institut der Universität zu Köln, Cologne, Germany
| | | | - D Teyssier
- Telespazio Vega UK for ESA/ESAC, Urbanizacion Villafranca del Castillo, Madrid, Spain
| | - O Berne
- IRAP, Université de Toulouse, CNRS, CNES, Université Paul Sabatier, Toulouse, France
| | - E Chambers
- USRA/SOFIA, NASA Ames Research Center, Moffett Field, CA, USA
| | - M Wolfire
- Department of Astronomy, University of Maryland, College Park, MD, USA
| | - S T Suri
- I. Physikalisches Institut der Universität zu Köln, Cologne, Germany
| | - R Guesten
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - J Stutzki
- I. Physikalisches Institut der Universität zu Köln, Cologne, Germany
| | - U U Graf
- I. Physikalisches Institut der Universität zu Köln, Cologne, Germany
| | - C Risacher
- Max-Planck-Institut für Radioastronomie, Bonn, Germany.,IRAM, St Martin d'Hères, France
| | - A G G M Tielens
- Leiden Observatory, Leiden University, Leiden, The Netherlands.
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Joblin C, Bron E, Pinto C, Pilleri P, Le Petit F, Gerin M, Le Bourlot J, Fuente A, Berne O, Goicoechea JR, Habart E, Köhler M, Teyssier D, Nagy Z, Montillaud J, Vastel C, Cernicharo J, Röllig M, Ossenkopf-Okada V, Bergin EA. Structure of photodissociation fronts in star-forming regions revealed by observations of high-J CO emission lines with Herschel. ASTRONOMY AND ASTROPHYSICS 2018; 615:A129. [PMID: 30185990 PMCID: PMC6120684 DOI: 10.1051/0004-6361/201832611] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
CONTEXT In bright photodissociation regions (PDRs) associated to massive star formation, the presence of dense "clumps" that are immersed in a less dense interclump medium is often proposed to explain the difficulty of models to account for the observed gas emission in high-excitation lines. AIMS We aim at presenting a comprehensive view of the modeling of the CO rotational ladder in PDRs, including the high-J lines that trace warm molecular gas at PDR interfaces. METHODS We observed the 12CO and 13CO ladders in two prototypical PDRs, the Orion Bar and NGC 7023 NW using the instruments onboard Herschel. We also considered line emission from key species in the gas cooling of PDRs (C+, O, H2) and other tracers of PDR edges such as OH and CH+. All the intensities are collected from Herschel observations, the literature and the Spitzer archive and are analyzed using the Meudon PDR code. RESULTS A grid of models was run to explore the parameter space of only two parameters: thermal gas pressure and a global scaling factor that corrects for approximations in the assumed geometry. We conclude that the emission in the high-J CO lines, which were observed up to J up =23 in the Orion Bar (J up =19 in NGC 7023), can only originate from small structures of typical thickness of a few 10-3 pc and at high thermal pressures (Pth ~ 108 K cm-3). CONCLUSIONS Compiling data from the literature, we found that the gas thermal pressure increases with the intensity of the UV radiation field given by G0, following a trend in line with recent simulations of the photoevaporation of illuminated edges of molecular clouds. This relation can help rationalising the analysis of high-J CO emission in massive star formation and provides an observational constraint for models that study stellar feedback on molecular clouds.
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Affiliation(s)
- C Joblin
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - E Bron
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - C Pinto
- Aix-Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
| | - P Pilleri
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - F Le Petit
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - M Gerin
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - J Le Bourlot
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
- Université Paris-Diderot, Paris, France
| | - A Fuente
- Observatorio Astronómico Nacional, Apdo. 112, 28803 Alcalá de Henares, Madrid, Spain
| | - O Berne
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - J R Goicoechea
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
| | - E Habart
- Institut d'Astrophysique Spatiale (IAS), Université Paris Sud & CNRS, 91405 Orsay, France
| | - M Köhler
- Institut d'Astrophysique Spatiale (IAS), Université Paris Sud & CNRS, 91405 Orsay, France
| | - D Teyssier
- European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
| | - Z Nagy
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - J Montillaud
- Institut Utinam, CNRS UMR 6213, OSU THETA, Université de Franche-Comté, 41bis avenue de l'Observatoire, 25000 Besançon, France
| | - C Vastel
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - J Cernicharo
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
| | - M Röllig
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - V Ossenkopf-Okada
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - E A Bergin
- Department of Astronomy, University of Michigan, 311 West Hall, 1085 S. University Avenue, Ann Arbor, MI 48109, USA
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Pabst CHM, Goicoechea JR, Teyssier D, Berné O, Ochsendorf BB, Wolfire MG, Higgins RD, Riquelme D, Risacher C, Pety J, Le Petit F, Roueff E, Bron E, Tielens AGGM. [Cii] emission from L1630 in the Orion B molecular cloud. ASTRONOMY AND ASTROPHYSICS 2017; 606:A29. [PMID: 28989177 PMCID: PMC5630115 DOI: 10.1051/0004-6361/201730881] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
CONTEXT L1630 in the Orion B molecular cloud, which includes the iconic Horsehead Nebula, illuminated by the star system σ Ori, is an example of a photodissociation region (PDR). In PDRs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes. AIMS Observations toward L1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field. Contrary to the well-studied Orion Molecular Cloud 1 (OMC1), which hosts much harsher conditions, L1630 has little star formation. Our goal is to relate the [Cii] fine-structure line emission to the physical conditions predominant in L1630 and compare it to studies of OMC1. METHODS The [Cii] 158 μm line emission of L1630 around the Horsehead Nebula, an area of 12' × 17', was observed using the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). RESULTS Of the [Cii] emission from the mapped area 95%, 13 L⊙, originates from the molecular cloud; the adjacent Hii region contributes only 5%, that is, 1 L⊙. From comparison with other data (CO(1-0)-line emission, far-infrared (FIR) continuum studies, emission from polycyclic aromatic hydrocarbons (PAHs)), we infer a gas density of the molecular cloud of nH ∼ 3 · 103 cm-3, with surface layers, including the Horsehead Nebula, having a density of up to nH ∼ 4 · 104 cm-3. The temperature of the surface gas is T ∼ 100 K. The average [Cii] cooling efficiency within the molecular cloud is 1.3 · 10-2. The fraction of the mass of the molecular cloud within the studied area that is traced by [Cii] is only 8%. Our PDR models are able to reproduce the FIR-[Cii] correlations and also the CO(1-0)-[Cii] correlations. Finally, we compare our results on the heating efficiency of the gas with theoretical studies of photoelectric heating by PAHs, clusters of PAHs, and very small grains, and find the heating efficiency to be lower than theoretically predicted, a continuation of the trend set by other observations. CONCLUSIONS In L1630 only a small fraction of the gas mass is traced by [Cii]. Most of the [Cii] emission in the mapped area stems from PDR surfaces. The layered edge-on structure of the molecular cloud and limitations in spatial resolution put constraints on our ability to relate different tracers to each other and to the physical conditions. From our study, we conclude that the relation between [Cii] emission and physical conditions is likely to be more complicated than often assumed. The theoretical heating efficiency is higher than the one we calculate from the observed [Cii] emission in the L1630 molecular cloud.
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Affiliation(s)
- C H M Pabst
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, Netherlands
| | - J R Goicoechea
- ICMM-CSIC, Calle Sor Juana Ines de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
| | - D Teyssier
- Herschel Science Center, ESA/ESAC, P.O. Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
| | - O Berné
- CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - B B Ochsendorf
- Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
| | - M G Wolfire
- Department of Astronomy, University of Maryland, College Park, MD 20742, USA
| | - R D Higgins
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - D Riquelme
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
| | - C Risacher
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
| | - J Pety
- IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - F Le Petit
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - E Roueff
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - E Bron
- ICMM-CSIC, Calle Sor Juana Ines de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - A G G M Tielens
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, Netherlands
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9
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Champion J, Berné O, Vicente S, Kamp I, Le Petit F, Gusdorf A, Joblin C, Goicoechea JR. Herschel survey and modelling of externally-illuminated photoevaporating protoplanetary disks. ASTRONOMY AND ASTROPHYSICS 2017; 604:A69. [PMID: 29093599 PMCID: PMC5662148 DOI: 10.1051/0004-6361/201629404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
CONTEXT Protoplanetary disks undergo substantial mass-loss by photoevaporation, a mechanism which is crucial to their dynamical evolution. However, the processes regulating the gas energetics have not been well constrained by observations so far. AIMS We aim at studying the processes involved in disk photoevaporation when it is driven by far-UV photons (i.e. 6 < E < 13.6 eV). METHODS We present a unique Herschel survey and new ALMA observations of four externally-illuminated photoevaporating disks (a.k.a. proplyds). For the analysis of these data, we developed a 1D model of the photodissociation region (PDR) of a proplyd, based on the Meudon PDR code and we computed the far infrared line emission. RESULTS With this model, we successfully reproduce most of the observations and derive key physical parameters, i.e. densities at the disk surface of about 106 cm-3 and local gas temperatures of about 1000 K. Our modelling suggests that all studied disks are found in a transitional regime resulting from the interplay between several heating and cooling processes that we identify. These differ from those dominating in classical PDRs i.e. grain photo-electric effect and cooling by [OI] and [CII] FIR lines. This specific energetic regime is associated to an equilibrium dynamical point of the photoevaporation flow: the mass-loss rate is self-regulated to keep the envelope column density at a value that maintains the temperature at the disk surface around 1000 K. From the physical parameters derived from our best-fit models, we estimate mass-loss rates - of the order of 10-7 M⊙/yr - that are in agreement with earlier spectroscopic observation of ionised gas tracers. This holds only if we assume photoevaporation in the supercritical regime where the evaporation flow is launched from the disk surface at sound speed. CONCLUSIONS We have identified the energetic regime regulating FUV-photoevaporation in proplyds. This regime could be implemented into models of the dynamical evolution of protoplanetary disks.
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Affiliation(s)
- J Champion
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - O Berné
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - S Vicente
- Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
- Institute of Astrophysics and Space Sciences (IA), Tapada da Ajuda - Edificio Leste - 2° Piso, 1349-018 Lisboa, Portugal
| | - I Kamp
- Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
| | - F Le Petit
- LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, F-92190 Meudon, France
| | - A Gusdorf
- LERMA, Observatoire de Paris, École normale supérieure, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75231, Paris, France
| | - C Joblin
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - J R Goicoechea
- Grupo de Astrofisica Molecular, Instituto de Ciencia de Materiales de Madrid (CSIC), E-28049, Madrid, Spain
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10
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Cuadrado S, Goicoechea JR, Cernicharo J, Fuente A, Pety J, Tercero B. Complex organic molecules in strongly UV-irradiated gas. ASTRONOMY AND ASTROPHYSICS 2017; 603:A124. [PMID: 29142326 PMCID: PMC5683355 DOI: 10.1051/0004-6361/201730459] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We investigate the presence of complex organic molecules (COMs) in strongly UV-irradiated interstellar molecular gas. We have carried out a complete millimetre (mm) line survey using the IRAM 30 m telescope towards the edge of the Orion Bar photodissociation region (PDR), close to the H2 dissociation front, a position irradiated by a very intense far-UV (FUV) radiation field. These observations have been complemented with 8.5″ resolution maps of the H2CO JKa,Kc = 51,5 → 41,4 and C18O J = 3 → 2 emission at 0.9 mm. Despite being a harsh environment, we detect more than 250 lines from COMs and related precursors: H2CO, CH3OH, HCO, H2CCO, CH3CHO, H2CS, HCOOH, CH3CN, CH2NH, HNCO, [Formula: see text] and HC3N (in decreasing order of abundance). For each species, the large number of detected lines allowed us to accurately constrain their rotational temperatures (Trot) and column densities (N). Owing to subthermal excitation and intricate spectroscopy of some COMs (symmetric- and asymmetric-top molecules such as CH3CN and H2CO, respectively), a correct determination of N and Trot requires building rotational population diagrams of their rotational ladders separately. The inferred column densities are in the 1011 - 1013cm-2 range. We also provide accurate upper limit abundances for chemically related molecules that might have been expected, but are not conclusively detected at the edge of the PDR (HDCO, CH3O, CH3NC, CH3CCH, CH3OCH3, HCOOCH3, CH3CH2OH, CH3CH2CN, and CH2CHCN). A non-thermodynamic equilibrium excitation analysis for molecules with known collisional rate coefficients suggests that some COMs arise from different PDR layers but we cannot resolve them spatially. In particular, H2CO and CH3CN survive in the extended gas directly exposed to the strong FUV flux (Tk = 150 - 250 K and Td ≳ 60 K), whereas CH3OH only arises from denser and cooler gas clumps in the more shielded PDR interior (Tk = 40 - 50 K). The non-detection of HDCO towards the PDR edge is consistent with the minor role of pure gas-phase deuteration at very high temperatures. We find a HCO/H2CO/CH3OH ≃ 1/5/3 abundance ratio. These ratios are different from those inferred in hot cores and shocks. Taking into account the elevated gas and dust temperatures at the edge of the Bar (mostly mantle-free grains), we suggest the following scenarios for the formation of COMs: (i) hot gas-phase reactions not included in current models; (ii) warm grain-surface chemistry; or (iii) the PDR dynamics is such that COMs or precursors formed in cold icy grains deeper inside the molecular cloud desorb and advect into the PDR.
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Affiliation(s)
- S Cuadrado
- Grupo de Astrofísica Molecular. Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
| | - J R Goicoechea
- Grupo de Astrofísica Molecular. Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
| | - J Cernicharo
- Grupo de Astrofísica Molecular. Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
| | - A Fuente
- Observatorio Astronómico Nacional, Apdo. 112, 28803 Alcalá de Henares, Madrid, Spain
| | - J Pety
- Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France
- LERMA, Observatoire de Paris, CNRS UMR 8112, École Normale Supérieure, PSL research university, 24 rue Lhomond, 75231, Paris Cedex 05, France
| | - B Tercero
- Grupo de Astrofísica Molecular. Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain
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11
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Parikka A, Habart E, Bernard-Salas J, Goicoechea JR, Abergel A, Pilleri P, Dartois E, Joblin C, Gerin M, Godard B. Spatial distribution of FIR rotationally excited CH + and OH emission lines in the Orion Bar PDR. ASTRONOMY AND ASTROPHYSICS 2017; 599:A20. [PMID: 28260804 PMCID: PMC5334792 DOI: 10.1051/0004-6361/201629445] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
CONTEXT The methylidyne cation (CH+) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500-1000 K) in photodissociation regions with high incident FUV radiation field. The excitation may also originate in dense gas (> 105 cm-3) followed by nonreactive collisions with H2, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH+ and OH correlate with the excited CO, a tracer of dense and warm gas, and formation pumping contributes to CH+ excitation. AIMS Our goal is to examine the spatial distribution of the rotationally excited CH+ and OH emission lines in the Orion Bar in order to establish their physical origin and main formation and excitation mechanisms. METHODS We present spatially sampled maps of the CH+ J=3-2 transition at 119.8 µm and the OH Λ-doublet at 84 µm in the Orion Bar over an area of 110″×110″ with Herschel (PACS). We compare the spatial distribution of these molecules with those of their chemical precursors, C+, O and H2, and tracers of warm and dense gas (high-J CO). We assess the spatial variation of CH+ J=2-1 velocity-resolved line profile at 1669 GHz with Herschel HIFI spectrometer observations. RESULTS The OH and especially CH+ lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH+ and OH morphologies indicate that CH+ formation and excitation are strongly related to the observed vibrationally excited H2. This, together with the observed broad CH+ line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 µm emission coincides with a bright young object, proplyd 244-440, which shows that OH can be an excellent tracer of UV-irradiated dense gas. CONCLUSIONS The spatial distribution of CH+ and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH+ J=3-2 excitation processes. The excitation of the OH Λ-doublet at 84 µm is mainly sensitive to the temperature and density.
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Affiliation(s)
- A Parikka
- Institut d'Astrophysique Spatiale, Université Paris-Saclay, 91405 Orsay Cedex, France; I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
| | - E Habart
- Institut d'Astrophysique Spatiale, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - J Bernard-Salas
- Department of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
| | - J R Goicoechea
- Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain
| | - A Abergel
- Institut d'Astrophysique Spatiale, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - P Pilleri
- Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France; CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - E Dartois
- Institut d'Astrophysique Spatiale, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - C Joblin
- Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France; CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - M Gerin
- LERMA, Observatoire de Paris, PSL Research University, Ecole Normale Supérieure, CNRS, 75014 Paris; Sorbonne Universités, UPMC Paris 06, CNRS, LERMA, 75005 Paris
| | - B Godard
- LERMA, Observatoire de Paris, PSL Research University, Ecole Normale Supérieure, CNRS, 75014 Paris; Sorbonne Universités, UPMC Paris 06, CNRS, LERMA, 75005 Paris
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12
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Tahani K, Plume R, Bergin EA, Tolls V, Phillips TG, Caux E, Cabrit S, Goicoechea JR, Goldsmith PF, Johnstone D, Lis DC, Pagani L, Menten KM, Müller HSP, Ossenkopf-Okada V, Pearson JC, van der Tak FFS. Analysis of the Herschel/HEXOS Spectral Survey Towards Orion South: A massive protostellar envelope with strong external irradiation. THE ASTROPHYSICAL JOURNAL 2016; 832:12. [PMID: 31844334 PMCID: PMC6914383 DOI: 10.3847/0004-637x/832/1/12] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We present results from a comprehensive submillimeter spectral survey toward the source Orion South, based on data obtained with the HIFI instrument aboard the Herschel Space Observatory, covering the frequency range 480 to 1900 GHz. We detect 685 spectral lines with S/N > 3σ, originating from 52 different molecular and atomic species. We model each of the detected species assuming conditions of Local Thermodynamic Equilibrium. This analysis provides an estimate of the physical conditions of Orion South (column density, temperature, source size, & V LSR ). We find evidence for three different cloud components: a cool (T ex ~ 20 - 40 K), spatially extended (> 60″), and quiescent (ΔVFWHM ~ 4 km s -1) component; a warmer (T ex ~ 80 - 100 K), less spatially extended (~ 30″), and dynamic (ΔVFWHM ~ 8 km s -1) component, which is likely affected by embedded outflows; and a kinematically distinct region (T ex > 100 K; V LSR ~ 8 km s -1), dominated by emission from species which trace ultraviolet irradiation, likely at the surface of the cloud. We find little evidence for the existence of a chemically distinct "hot core" component, likely due to the small filling factor of the hot core or hot cores within the Herschel beam. We find that the chemical composition of the gas in the cooler, quiescent component of Orion South more closely resembles that of the quiescent ridge in Orion-KL. The gas in the warmer, dynamic component, however, more closely resembles that of the Compact Ridge and Plateau regions of Orion-KL, suggesting that higher temperatures and shocks also have an influence on the overall chemistry of Orion South.
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Affiliation(s)
- K Tahani
- Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada T2N 1N4
| | - R Plume
- Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada T2N 1N4
| | - E A Bergin
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
| | - V Tolls
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
| | - T G Phillips
- California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA
| | - E Caux
- Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France
- CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - S Cabrit
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - J R Goicoechea
- Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - P F Goldsmith
- Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
| | - D Johnstone
- National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
| | - D C Lis
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
- California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA
| | - L Pagani
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - K M Menten
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
| | - H S P Müller
- I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - V Ossenkopf-Okada
- I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - J C Pearson
- Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
| | - F F S van der Tak
- SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
- Kapteyn Astronomical Institute, Groningen, The Netherlands
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13
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Goicoechea JR, Pety J, Cuadrado S, Cernicharo J, Chapillon E, Fuente A, Gerin M, Joblin C, Marcelino N, Pilleri P. Compression and ablation of the photo-irradiated molecular cloud the Orion Bar. Nature 2016; 537:207-209. [PMID: 27509859 PMCID: PMC5111730 DOI: 10.1038/nature18957] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Accepted: 06/08/2016] [Indexed: 11/26/2022]
Abstract
The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Owing to the close distance to Orion (about 1,350 light-year), the effects of stellar feedback on the parental cloud can be studied in detail. Visible-light observations of the Bar1 show that the transition between the hot ionised gas and the warm neutral atomic gas (the ionisation front) is spatially well separated from the transition from atomic to molecular gas (the dissociation front): about 15 arcseconds or 6,200 astronomical units. (One astronomical unit is the Earth-Sun distance.) Static equilibrium models2,3 used to interpret previous far-infrared and radio observations of the neutral gas in the Bar4,5,6 (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure consisting of dense clumps embedded in a lower density extended gas component. Here we report 1 arcsecond resolution millimetre-wave images that allow us to resolve the molecular cloud surface and constrain the gas density and temperature structures at small spatial scales. In contrast to stationary model predictions7,8,9, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. These observations reveal a fragmented ridge of high-density substructures, photo-ablative gas flows and instabilities at the molecular cloud surface. They suggest that the cloud edge has been compressed by a high-pressure wave that currently moves into the molecular cloud. The images demonstrate that dynamical and nonequilibrium effects are important. Thus, they should be included in any realistic description of irradiated interstellar matter.
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Affiliation(s)
- Javier R Goicoechea
- Grupo de Astrofísica Molecular, Instituto de Ciencia de Materiales de Madrid (CSIC), Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - Jérôme Pety
- Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France.,Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA), Observatoire de Paris, Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Rechersche (UMR) 8112, École Normale Supérieure, PSL Research University, 24 rue Lhomond, 75231, Paris Cedex 05, France
| | - Sara Cuadrado
- Grupo de Astrofísica Molecular, Instituto de Ciencia de Materiales de Madrid (CSIC), Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - José Cernicharo
- Grupo de Astrofísica Molecular, Instituto de Ciencia de Materiales de Madrid (CSIC), Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - Edwige Chapillon
- Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France.,Laboratoire d'Astrophysique de Bordeaux (LAB), Université de Bordeaux, UMR 5804, F-33270 Floirac, France.,CNRS, LAB, UMR 5804, F-33270 Floirac, France
| | - Asunción Fuente
- Observatorio Astronómico Nacional (OAN-IGN). Apartado 112, 28803 Alcalá de Henares, Spain
| | - Maryvonne Gerin
- Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA), Observatoire de Paris, Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Rechersche (UMR) 8112, École Normale Supérieure, PSL Research University, 24 rue Lhomond, 75231, Paris Cedex 05, France.,Sorbonne Universités, Université Pierre et Marie Curie (UPMC), Université Paris 06, 75000, France
| | - Christine Joblin
- Université de Toulouse, Université Paul-Sabatier-Observatoire Midi-Pyrénées (UPS-OMP), Institut de Recherche en Astrophysique et Planétologie (IRAP), 31028, Toulouse, France.,CNRS, IRAP, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse, France
| | - Nuria Marcelino
- Grupo de Astrofísica Molecular, Instituto de Ciencia de Materiales de Madrid (CSIC), Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - Paolo Pilleri
- Université de Toulouse, Université Paul-Sabatier-Observatoire Midi-Pyrénées (UPS-OMP), Institut de Recherche en Astrophysique et Planétologie (IRAP), 31028, Toulouse, France.,CNRS, IRAP, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse, France
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