Laurent Verstraete - Academia.edu (original) (raw)
Papers by Laurent Verstraete
Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedb... more 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 ...
Astronomy and Astrophysics, 2021
The large disparity in physical conditions from the diffuse interstellar medium (ISM) to denser c... more The large disparity in physical conditions from the diffuse interstellar medium (ISM) to denser clouds such as photon-dominated regions (PDRs) triggers an evolution of the dust properties (i.e. composition, size, and shape). The gas physics and chemistry are tightly connected to these dust properties and are therefore affected by dust evolution and especially the nano-grain depletion in the outer irradiated part of PDRs. We highlight the influence of nano-grain depletion on the gas physics and chemistry in the Horsehead nebula, a prototypical PDR. We used a model for atomic and molecular gas in PDRs, the Meudon PDR code, using diffuse ISM-like dust and Horsehead-like dust to study the influence of nano-grain depletion on the gas physics and chemistry, focusing on the impact on photoelectric heating and H2 formation and, therefore, on the H2 gas lines. We find that nano-grain depletion in the Horsehead strongly affects gas heating through the photoelectric effect and thus the gas tem...
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interste... more Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has lead to important progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the interstellar medium, where Tgas . 500 K, nH 100 to 10 5 cm 3 and the electron density is a few 10 4 .
Astronomy & Astrophysics, 2020
Context. Micro-physical processes on interstellar dust surfaces are tightly connected to dust pro... more Context. 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 a more thorough understanding of interstellar dust. Aims. We highlight dust evolution in the Horsehead nebula photon-dominated region. Methods. We used Spitzer/IRAC (3.6, 4.5, 5.8 and 8 μm) and Spitzer/MIPS (24 μm) together with Herschel/PACS (70 and 160 μm) and Herschel/SPIRE (250, 350 and 500 μm) to map the spatial distribution of dust in the Horsehead nebula over the entire emission spectral range. We modelled dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC. Results. We find ...
Proceedings of Advancing Astrophysics with the Square Kilometre Array — PoS(AASKA14), 2015
In this chapter, we will outline the scientific motivation for studying Anomalous Microwave Emiss... more In this chapter, we will outline the scientific motivation for studying Anomalous Microwave Emission (AME) with the SKA. AME is thought to be due to electric dipole radiation from small spinning dust grains, although thermal fluctuations of magnetic dust grains may also contribute. Studies of this mysterious component would shed light on the emission mechanism, which then opens up a new window onto the interstellar medium (ISM). AME is emitted mostly in the frequency range ∼ 10-100 GHz, and thus the SKA has the potential of measuring the low frequency side of the AME spectrum, particularly in band 5. Science targets include dense molecular clouds in the Milky Way, as well as extragalactic sources. We also discuss the possibility of detecting rotational line emission from Poly-cyclic Aromatic Hydrocarbons (PAHs), which could be the main carriers of AME. Detecting PAH lines of a given spacing would allow for a definitive identification of specific PAH species.
Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013), 2014
Results from the latest generation of surveys in the microwave and submillimeter domain (Planck, ... more Results from the latest generation of surveys in the microwave and submillimeter domain (Planck, Herschel) suggest that the optical properties of dust in the diffuse interstellar medium are not fixed, but change from region to region, possibly due to dust evolution. Interstellar dust models need to explain this variability. The hydrogenated amorphous carbons collectively known as a-C(:H) are very interesting candidate dust components in this respect: their optical properties can be modified by ultraviolet photoprocessing, so that the dust properties will vary with the environmental conditions and previous dust history. We are currently working on a model containing a-C(:H) to determine what physical parameters can reproduce the variations of dust emission observed by Planck. We show here the effects of varying the amount of a-C(:H) photoprocessing and of carbon accretion from the gas phase. * Speaker.
Proceedings of CMB and Physics of the Early Universe — PoS(CMB2006), 2007
Measurements of CMB fluctuations will be performed most sensitively between 1 and 100 GHz (Banday... more Measurements of CMB fluctuations will be performed most sensitively between 1 and 100 GHz (Banday et al. 2003, Fig. 6). In this frequency range however, several foregrounds limit the access to the CMB. Among these, the so-called anomalous emission which is probably of dust origin and is the least well known, motivating further theoretical and observational studies. A better understanding of this emission will help remove galactic foregrounds and will bring new constraints on interstellar grains. We discuss here several dust emission processes that could be at the origin of this anomalous emission. Emphasis is given to spinning, small dust grains which seem to be favored by recent data analysis.
Astronomy & Astrophysics, 2018
Context. Current dust models are challenged by the dust properties inferred from the analysis of ... more Context. Current dust models are challenged by the dust properties inferred from the analysis of Planck observations in total and polarized emission. Aims. We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight (0.5 < AV < 2.5). Methods. We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, total and polarized spectral energy distributions (SEDs) with polycyclic aromatic hydrocarbons, astrosilicate and amorphous carbon (a-C) grains. The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. Results. With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio P353∕pV derived with Planck data. Successful models are those using prolate astrosilicate grains with an...
The ISO-SWS spectra of two bright reflection nebulae, NGC 7023 and NGC 2023, are presented. We di... more The ISO-SWS spectra of two bright reflection nebulae, NGC 7023 and NGC 2023, are presented. We discuss the emission of molecular hydrogen from these photodissociated interfaces. Details of the aromatic infrared band profiles as well as the continuum emission are also analysed. The ISO-LWS spectrum of NGC 7023 is also presented, at two positions in the nebula. The dust temperature at the brightest far-infrared position of NGC 7023 is estimated to be 45 K.
Astronomy and Astrophysics
The detection of a new 16.4 mu m emission feature in the ISO-SWS spectra of NGC 7023, M17, and th... more The detection of a new 16.4 mu m emission feature in the ISO-SWS spectra of NGC 7023, M17, and the Orion Bar is reported. Previous laboratory experiments measured a mode near this wavelength in spectra of PAHs (Polycyclic Aromatic Hydrocarbons), and so we suggest the new interstellar 16.4 mu m feature could be assigned to low-frequency vibrations of PAHs. The best carrier candidates seem to be PAH molecules containing pentagonal rings. based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: the United Kingdom, France, the Netherlands, Germany), and with the participation of ISAS and NASA.
Astronomy & Astrophysics, 2000
We present mid-infrared spectro-imagery and high-resolution spectroscopy of the Orion bar and of ... more We present mid-infrared spectro-imagery and high-resolution spectroscopy of the Orion bar and of a region in the Orion nebula. These observations have been obtained in the Guaranteed Time with the Circular Variable Filters of the ISO camera (CAM-CVF) and with the Short Wavelength Spectrometer (SWS), on board the European Infrared Space Observatory (ISO). Our data shows emission from amorphous silicate
Molecular Hydrogen in Space
Cold molecular hydrogen, a possibly dominant gas fraction in galaxies, does not radiate due to th... more Cold molecular hydrogen, a possibly dominant gas fraction in galaxies, does not radiate due to the symmetry and small moment of inertia of the molecule. The only tracers of cold H2, the rotational lines of CO and dust thermal emission operate only in metal-rich environments. By detecting the lowest rotational lines of H2 at unexpected levels in cold diffuse medium,
The Astrophysical Journal, 1993
Subarcsecond 8 and 10 microns and diffraction-limited 19 microns imaging of the inner few hundred... more Subarcsecond 8 and 10 microns and diffraction-limited 19 microns imaging of the inner few hundred parsecs of the Seyfert nucleus in NGC 1068 shows the emission to be extended over a region of ˜70 × 140 pc. In particular, 10.3 microns images with spatial resolutions of 0&amp;quot;5 or better reveal that the warm dust is associated with the narrow-line clouds
Space Science Reviews, 2005
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interste... more Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has lead to important progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the interstellar medium, where Tgas 500 K, nH ∼ 100 to 10 5 cm −3 and the electron density is a few 10 −4 .
Space Science Reviews, 2005
Observations of H2 line emission in galactic and extragalactic environments obtained with the Inf... more Observations of H2 line emission in galactic and extragalactic environments obtained with the Infrared Space Observatory (ISO) are reviewed. The diagnostic capability of H2 observations is illustrated. We discuss what one has learned about such diverse astrophysical sources as photon-dominated regions, shocks, young stellar objects, planetary nebulae and starburst galaxies from ISO observations of H2 emission. In this context, we emphasise use of measured H2 line intensities to infer important physical quantities such as the gas temperature, gas density and radiation field and we discuss the different possible excitation mechanisms of H2. We also briefly consider future prospects for observation of H2 from space and from the ground.
Faraday Discussions, 2014
Observational evidence seems to indicate that the depletion of interstellar carbon into dust show... more Observational evidence seems to indicate that the depletion of interstellar carbon into dust shows rather wide variations and that carbon undergoes rather rapid recycling in the interstellar medium (ISM). Small hydrocarbon grains are processed in photo-dissociation regions by UV photons, by ion and electron collisions in interstellar shock waves and by cosmic rays. A significant fraction of hydrocarbon dust must therefore be re-formed by accretion in the dense, molecular ISM. A new dust model (Jones et al., Astron. Astrophys., 2013, 558, A62) shows that variations in the dust observables in the diffuse interstellar medium (nH ≤ 103 cm−3), can be explained by systematic and environmentally-driven changes in the small hydrocarbon grain population. Here we explore the consequences of gas-phase carbon accretion onto the surfaces of grains in the transition regions between the diffuse ISM and molecular clouds (e.g., Jones, Astron. Astrophys., 2013, 555, A39). We find that significant car...
Astronomy & Astrophysics, 2013
Aims. We investigate and quantify the effects of the electron collisional heating of dust in a ho... more Aims. We investigate and quantify the effects of the electron collisional heating of dust in a hot gas and compare this with photon heating by the interstellar radiation field. Methods. We compare the rate of energy absorption by dust due to electron collisional and photon heating as a function of the physical conditions of the gas and the ambient radiation field. We calculate the resulting dust spectral energy distributions (SEDs) for different environments. Results. We find that electron collisions and grain charging effects in a hot gas (10 6 −10 7 K) rapidly destroy small carbonaceous particles and result in a minimum particle size of the order of a few nm. The charging due to the emission of secondary electrons is important and leads to high electric potentials, which quickly destroy the small grains by field ion emission. In the case of weak interstellar radiation fields (G 0 ∼ 0.1), electron collisional heating can be the dominant heating process and therefore makes an important contribution to the dust thermal emission. Conclusions. Collisions of electrons with dust grains, in a hot gas, lead to important changes in the dust SED, as a result of their high energy input. We find that grain charge effects and accompanying erosion need to be taken into account in the calculation of the dust SED. The power absorbed by the dust as a result of electron collisions in a hot tenuous gas can be larger than that due to photon absorption in the intergalactic medium close to a galaxy where the radiation field is weak (G 0 < ∼ 0.1).
Astronomy & Astrophysics, 2003
We present a comparison of the gas and dust properties of the dense interstellar matter in six ne... more We present a comparison of the gas and dust properties of the dense interstellar matter in six nearby star−forming regions (d < 500 pc): ρ Oph, Cha I, R CrA, IC 348, NGC 1333, and Orion. We measure from Chandra and XMM−Newton observations the X-ray absorption toward pre-main sequence stars (PMS) without accretion disks (i.e., Class III sources) to obtain the total hydrogen column density N H,X. For these sources we take from the literature the corresponding dust extinction in the near−infrared, A J , or when unavailable we derive it from SED fitting using the available DENIS, 2MASS, ISOCAM and other data. We then compare N H,X and A J for each object, up to unprecedently high extinction. For the ρ Oph dark cloud with a relatively large sample of 20 bona-fide Class III sources, we probe the extinction up to A J < ∼ 14 (A V < ∼ 45), and find a best-fit linear relation N H,X /A J = 5.6 (± 0.4) × 10 21 cm −2 mag −1 , adopting standard ISM abundances. The other regions reveal a large dispersion in the N H,X /A J ratio for each source but for lack of adequate IR data these studies remain limited to moderate extinctions (A J < ∼ 1.5 or A V < ∼ 5). For ρ Oph, the N H,X /A J ratio is significantly lower (> ∼ 2σ) than the galactic value, derived using the standard extinction curve (R V = 3.1). This result is consistent with the recent downwards revision of the metallicity of the Sun and stars in the solar vicinity. We find that the ρ Oph dense cloud has the same metallicity than the local ISM when assuming that the galactic gas-to-dust ratio remains unchanged. The difference between galactic and local values of the gas-to-dust ratio can thus be attributed entirely to a difference in metallicity.
Astronomy and Astrophysics, 2010
Context. The Galactic anomalous microwave emission detected between 10 and 90 GHz is a major fore... more Context. The Galactic anomalous microwave emission detected between 10 and 90 GHz is a major foreground to CMB fluctuations. Well correlated with dust emission at 100 μm, the anomalous foreground is interstellar but its origin is still debated. Possible carriers for this emission are spinning, small dust grains carrying a permanent electric dipole. Aims. To probe the origin of the anomalous foreground, we compare microwave data to dust IR emission on an angular scale of 1 • , and search for specific signatures predicted by models of spinning dust. Methods. For the anomalous foreground, we use the 23 GHz all-sky map deduced from WMAP data by Miville-Deschênes and collaborators. The IR dust emission is traced by IRAS data. Models show that spinning dust emission is little sensitive to the intensity of the radiation field (G 0) for 10 ν 30 GHz, while the mid-IR emission produced by the same small dust grains is proportional to G 0. To test this behaviour in our comparison, we derive G 0 from the dust temperature maps of Schlegel and collaborators. Results. From all-sky maps, we show that the anomalous foreground is more strongly correlated with the emission of small grains (at 12 μm) than with that of large grains (at 100 μm). In addition, we show that the former correlation is significantly improved when the 12 μm flux is divided by G 0 , as predicted by current models of spinning dust. The results apply to angular scales greater than 1 •. Finally, from a model fit of the anomalous foreground, we deduce physical properties for Polycyclic Aromatic Hydrocarbons that are in good agreement with those deduced from mid-IR spectroscopy.
Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedb... more 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 ...
Astronomy and Astrophysics, 2021
The large disparity in physical conditions from the diffuse interstellar medium (ISM) to denser c... more The large disparity in physical conditions from the diffuse interstellar medium (ISM) to denser clouds such as photon-dominated regions (PDRs) triggers an evolution of the dust properties (i.e. composition, size, and shape). The gas physics and chemistry are tightly connected to these dust properties and are therefore affected by dust evolution and especially the nano-grain depletion in the outer irradiated part of PDRs. We highlight the influence of nano-grain depletion on the gas physics and chemistry in the Horsehead nebula, a prototypical PDR. We used a model for atomic and molecular gas in PDRs, the Meudon PDR code, using diffuse ISM-like dust and Horsehead-like dust to study the influence of nano-grain depletion on the gas physics and chemistry, focusing on the impact on photoelectric heating and H2 formation and, therefore, on the H2 gas lines. We find that nano-grain depletion in the Horsehead strongly affects gas heating through the photoelectric effect and thus the gas tem...
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interste... more Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has lead to important progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the interstellar medium, where Tgas . 500 K, nH 100 to 10 5 cm 3 and the electron density is a few 10 4 .
Astronomy & Astrophysics, 2020
Context. Micro-physical processes on interstellar dust surfaces are tightly connected to dust pro... more Context. 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 a more thorough understanding of interstellar dust. Aims. We highlight dust evolution in the Horsehead nebula photon-dominated region. Methods. We used Spitzer/IRAC (3.6, 4.5, 5.8 and 8 μm) and Spitzer/MIPS (24 μm) together with Herschel/PACS (70 and 160 μm) and Herschel/SPIRE (250, 350 and 500 μm) to map the spatial distribution of dust in the Horsehead nebula over the entire emission spectral range. We modelled dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC. Results. We find ...
Proceedings of Advancing Astrophysics with the Square Kilometre Array — PoS(AASKA14), 2015
In this chapter, we will outline the scientific motivation for studying Anomalous Microwave Emiss... more In this chapter, we will outline the scientific motivation for studying Anomalous Microwave Emission (AME) with the SKA. AME is thought to be due to electric dipole radiation from small spinning dust grains, although thermal fluctuations of magnetic dust grains may also contribute. Studies of this mysterious component would shed light on the emission mechanism, which then opens up a new window onto the interstellar medium (ISM). AME is emitted mostly in the frequency range ∼ 10-100 GHz, and thus the SKA has the potential of measuring the low frequency side of the AME spectrum, particularly in band 5. Science targets include dense molecular clouds in the Milky Way, as well as extragalactic sources. We also discuss the possibility of detecting rotational line emission from Poly-cyclic Aromatic Hydrocarbons (PAHs), which could be the main carriers of AME. Detecting PAH lines of a given spacing would allow for a definitive identification of specific PAH species.
Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013), 2014
Results from the latest generation of surveys in the microwave and submillimeter domain (Planck, ... more Results from the latest generation of surveys in the microwave and submillimeter domain (Planck, Herschel) suggest that the optical properties of dust in the diffuse interstellar medium are not fixed, but change from region to region, possibly due to dust evolution. Interstellar dust models need to explain this variability. The hydrogenated amorphous carbons collectively known as a-C(:H) are very interesting candidate dust components in this respect: their optical properties can be modified by ultraviolet photoprocessing, so that the dust properties will vary with the environmental conditions and previous dust history. We are currently working on a model containing a-C(:H) to determine what physical parameters can reproduce the variations of dust emission observed by Planck. We show here the effects of varying the amount of a-C(:H) photoprocessing and of carbon accretion from the gas phase. * Speaker.
Proceedings of CMB and Physics of the Early Universe — PoS(CMB2006), 2007
Measurements of CMB fluctuations will be performed most sensitively between 1 and 100 GHz (Banday... more Measurements of CMB fluctuations will be performed most sensitively between 1 and 100 GHz (Banday et al. 2003, Fig. 6). In this frequency range however, several foregrounds limit the access to the CMB. Among these, the so-called anomalous emission which is probably of dust origin and is the least well known, motivating further theoretical and observational studies. A better understanding of this emission will help remove galactic foregrounds and will bring new constraints on interstellar grains. We discuss here several dust emission processes that could be at the origin of this anomalous emission. Emphasis is given to spinning, small dust grains which seem to be favored by recent data analysis.
Astronomy & Astrophysics, 2018
Context. Current dust models are challenged by the dust properties inferred from the analysis of ... more Context. Current dust models are challenged by the dust properties inferred from the analysis of Planck observations in total and polarized emission. Aims. We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight (0.5 < AV < 2.5). Methods. We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, total and polarized spectral energy distributions (SEDs) with polycyclic aromatic hydrocarbons, astrosilicate and amorphous carbon (a-C) grains. The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. Results. With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio P353∕pV derived with Planck data. Successful models are those using prolate astrosilicate grains with an...
The ISO-SWS spectra of two bright reflection nebulae, NGC 7023 and NGC 2023, are presented. We di... more The ISO-SWS spectra of two bright reflection nebulae, NGC 7023 and NGC 2023, are presented. We discuss the emission of molecular hydrogen from these photodissociated interfaces. Details of the aromatic infrared band profiles as well as the continuum emission are also analysed. The ISO-LWS spectrum of NGC 7023 is also presented, at two positions in the nebula. The dust temperature at the brightest far-infrared position of NGC 7023 is estimated to be 45 K.
Astronomy and Astrophysics
The detection of a new 16.4 mu m emission feature in the ISO-SWS spectra of NGC 7023, M17, and th... more The detection of a new 16.4 mu m emission feature in the ISO-SWS spectra of NGC 7023, M17, and the Orion Bar is reported. Previous laboratory experiments measured a mode near this wavelength in spectra of PAHs (Polycyclic Aromatic Hydrocarbons), and so we suggest the new interstellar 16.4 mu m feature could be assigned to low-frequency vibrations of PAHs. The best carrier candidates seem to be PAH molecules containing pentagonal rings. based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: the United Kingdom, France, the Netherlands, Germany), and with the participation of ISAS and NASA.
Astronomy & Astrophysics, 2000
We present mid-infrared spectro-imagery and high-resolution spectroscopy of the Orion bar and of ... more We present mid-infrared spectro-imagery and high-resolution spectroscopy of the Orion bar and of a region in the Orion nebula. These observations have been obtained in the Guaranteed Time with the Circular Variable Filters of the ISO camera (CAM-CVF) and with the Short Wavelength Spectrometer (SWS), on board the European Infrared Space Observatory (ISO). Our data shows emission from amorphous silicate
Molecular Hydrogen in Space
Cold molecular hydrogen, a possibly dominant gas fraction in galaxies, does not radiate due to th... more Cold molecular hydrogen, a possibly dominant gas fraction in galaxies, does not radiate due to the symmetry and small moment of inertia of the molecule. The only tracers of cold H2, the rotational lines of CO and dust thermal emission operate only in metal-rich environments. By detecting the lowest rotational lines of H2 at unexpected levels in cold diffuse medium,
The Astrophysical Journal, 1993
Subarcsecond 8 and 10 microns and diffraction-limited 19 microns imaging of the inner few hundred... more Subarcsecond 8 and 10 microns and diffraction-limited 19 microns imaging of the inner few hundred parsecs of the Seyfert nucleus in NGC 1068 shows the emission to be extended over a region of ˜70 × 140 pc. In particular, 10.3 microns images with spatial resolutions of 0&amp;quot;5 or better reveal that the warm dust is associated with the narrow-line clouds
Space Science Reviews, 2005
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interste... more Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has lead to important progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the interstellar medium, where Tgas 500 K, nH ∼ 100 to 10 5 cm −3 and the electron density is a few 10 −4 .
Space Science Reviews, 2005
Observations of H2 line emission in galactic and extragalactic environments obtained with the Inf... more Observations of H2 line emission in galactic and extragalactic environments obtained with the Infrared Space Observatory (ISO) are reviewed. The diagnostic capability of H2 observations is illustrated. We discuss what one has learned about such diverse astrophysical sources as photon-dominated regions, shocks, young stellar objects, planetary nebulae and starburst galaxies from ISO observations of H2 emission. In this context, we emphasise use of measured H2 line intensities to infer important physical quantities such as the gas temperature, gas density and radiation field and we discuss the different possible excitation mechanisms of H2. We also briefly consider future prospects for observation of H2 from space and from the ground.
Faraday Discussions, 2014
Observational evidence seems to indicate that the depletion of interstellar carbon into dust show... more Observational evidence seems to indicate that the depletion of interstellar carbon into dust shows rather wide variations and that carbon undergoes rather rapid recycling in the interstellar medium (ISM). Small hydrocarbon grains are processed in photo-dissociation regions by UV photons, by ion and electron collisions in interstellar shock waves and by cosmic rays. A significant fraction of hydrocarbon dust must therefore be re-formed by accretion in the dense, molecular ISM. A new dust model (Jones et al., Astron. Astrophys., 2013, 558, A62) shows that variations in the dust observables in the diffuse interstellar medium (nH ≤ 103 cm−3), can be explained by systematic and environmentally-driven changes in the small hydrocarbon grain population. Here we explore the consequences of gas-phase carbon accretion onto the surfaces of grains in the transition regions between the diffuse ISM and molecular clouds (e.g., Jones, Astron. Astrophys., 2013, 555, A39). We find that significant car...
Astronomy & Astrophysics, 2013
Aims. We investigate and quantify the effects of the electron collisional heating of dust in a ho... more Aims. We investigate and quantify the effects of the electron collisional heating of dust in a hot gas and compare this with photon heating by the interstellar radiation field. Methods. We compare the rate of energy absorption by dust due to electron collisional and photon heating as a function of the physical conditions of the gas and the ambient radiation field. We calculate the resulting dust spectral energy distributions (SEDs) for different environments. Results. We find that electron collisions and grain charging effects in a hot gas (10 6 −10 7 K) rapidly destroy small carbonaceous particles and result in a minimum particle size of the order of a few nm. The charging due to the emission of secondary electrons is important and leads to high electric potentials, which quickly destroy the small grains by field ion emission. In the case of weak interstellar radiation fields (G 0 ∼ 0.1), electron collisional heating can be the dominant heating process and therefore makes an important contribution to the dust thermal emission. Conclusions. Collisions of electrons with dust grains, in a hot gas, lead to important changes in the dust SED, as a result of their high energy input. We find that grain charge effects and accompanying erosion need to be taken into account in the calculation of the dust SED. The power absorbed by the dust as a result of electron collisions in a hot tenuous gas can be larger than that due to photon absorption in the intergalactic medium close to a galaxy where the radiation field is weak (G 0 < ∼ 0.1).
Astronomy & Astrophysics, 2003
We present a comparison of the gas and dust properties of the dense interstellar matter in six ne... more We present a comparison of the gas and dust properties of the dense interstellar matter in six nearby star−forming regions (d < 500 pc): ρ Oph, Cha I, R CrA, IC 348, NGC 1333, and Orion. We measure from Chandra and XMM−Newton observations the X-ray absorption toward pre-main sequence stars (PMS) without accretion disks (i.e., Class III sources) to obtain the total hydrogen column density N H,X. For these sources we take from the literature the corresponding dust extinction in the near−infrared, A J , or when unavailable we derive it from SED fitting using the available DENIS, 2MASS, ISOCAM and other data. We then compare N H,X and A J for each object, up to unprecedently high extinction. For the ρ Oph dark cloud with a relatively large sample of 20 bona-fide Class III sources, we probe the extinction up to A J < ∼ 14 (A V < ∼ 45), and find a best-fit linear relation N H,X /A J = 5.6 (± 0.4) × 10 21 cm −2 mag −1 , adopting standard ISM abundances. The other regions reveal a large dispersion in the N H,X /A J ratio for each source but for lack of adequate IR data these studies remain limited to moderate extinctions (A J < ∼ 1.5 or A V < ∼ 5). For ρ Oph, the N H,X /A J ratio is significantly lower (> ∼ 2σ) than the galactic value, derived using the standard extinction curve (R V = 3.1). This result is consistent with the recent downwards revision of the metallicity of the Sun and stars in the solar vicinity. We find that the ρ Oph dense cloud has the same metallicity than the local ISM when assuming that the galactic gas-to-dust ratio remains unchanged. The difference between galactic and local values of the gas-to-dust ratio can thus be attributed entirely to a difference in metallicity.
Astronomy and Astrophysics, 2010
Context. The Galactic anomalous microwave emission detected between 10 and 90 GHz is a major fore... more Context. The Galactic anomalous microwave emission detected between 10 and 90 GHz is a major foreground to CMB fluctuations. Well correlated with dust emission at 100 μm, the anomalous foreground is interstellar but its origin is still debated. Possible carriers for this emission are spinning, small dust grains carrying a permanent electric dipole. Aims. To probe the origin of the anomalous foreground, we compare microwave data to dust IR emission on an angular scale of 1 • , and search for specific signatures predicted by models of spinning dust. Methods. For the anomalous foreground, we use the 23 GHz all-sky map deduced from WMAP data by Miville-Deschênes and collaborators. The IR dust emission is traced by IRAS data. Models show that spinning dust emission is little sensitive to the intensity of the radiation field (G 0) for 10 ν 30 GHz, while the mid-IR emission produced by the same small dust grains is proportional to G 0. To test this behaviour in our comparison, we derive G 0 from the dust temperature maps of Schlegel and collaborators. Results. From all-sky maps, we show that the anomalous foreground is more strongly correlated with the emission of small grains (at 12 μm) than with that of large grains (at 100 μm). In addition, we show that the former correlation is significantly improved when the 12 μm flux is divided by G 0 , as predicted by current models of spinning dust. The results apply to angular scales greater than 1 •. Finally, from a model fit of the anomalous foreground, we deduce physical properties for Polycyclic Aromatic Hydrocarbons that are in good agreement with those deduced from mid-IR spectroscopy.