C. Joblin, A. Tielens, K. Sellgren, M. Werner, J. Ingalls, John-David T. Smith, T. Carleton
The fullerene C 60 has four infrared active vibrational transitions at 7.0, 8.5, 17.5 and 18.9 μ m. We have previously observed emission features at 17.4 and 18.9 μ m in the reflection nebula NGC 7023 and demonstrated spatial correlations suggestive of a common origin. We now confirm the identification of these features with C 60 by detecting a third emission feature at 7.04 ± 0.05 μ m at a position of strong 18.9 μ m emission in NGC 7023. We also report the detection of these three features in the reflection nebula NGC 2023. We show with spectroscopic mapping of NGC 7023 that the 18.9 μ m feature peaks on the central star, that the 16.4 μ m emission feature due to PAHs peaks between the star and a nearby photodissociation front, and that the 17.4 μ m feature is a blend of a PAH feature and C 60 . The derived C 60 abundance is consistent with that from previous upper limits and possible fullerene detections in the interstellar medium.
{"title":"Confirmation of C60 in the Reflection Nebula NGC 7023","authors":"C. Joblin, A. Tielens, K. Sellgren, M. Werner, J. Ingalls, John-David T. Smith, T. Carleton","doi":"10.1051/eas/1146022","DOIUrl":"https://doi.org/10.1051/eas/1146022","url":null,"abstract":"The fullerene C 60 has four infrared active vibrational transitions at 7.0, 8.5, 17.5 and 18.9 μ m. We have previously observed emission features at\u0000 17.4 and 18.9 μ m in the reflection nebula NGC 7023 and demonstrated\u0000 spatial correlations suggestive of a common origin. We now confirm the identification of\u0000 these features with C 60 by detecting a third emission feature at\u0000 7.04 ± 0.05 μ m at a position of strong 18.9 μ m emission\u0000 in NGC 7023. We also report the detection of these three features in the reflection nebula\u0000 NGC 2023. We show with spectroscopic mapping of NGC 7023 that the 18.9 μ m\u0000 feature peaks on the central star, that the 16.4 μ m emission feature due\u0000 to PAHs peaks between the star and a nearby photodissociation front, and that the 17.4\u0000 μ m feature is a blend of a PAH feature and C 60 . The derived\u0000 C 60 abundance is consistent with that from previous upper limits and possible\u0000 fullerene detections in the interstellar medium.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"516 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116226008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ji Hoon Kim, M. Im, Hyung Mok Lee, Myung Gyoon Lee
With advancement of infrared space telescopes during the past decade, infrared wavelength regime has been a focal point to study various properties of galaxies with respect to evolution of galaxies. Polycyclic Aromatic Hydrocarbons (PAHs) have emerged as one of the most important features since these features dominate the mid-infrared spectra of galaxies. These PAH features provide a great handle to calibrate star formation rates and diagnose ionized states of grains. However, the PAH 3.3 μ m feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability, although it will be the only PAH feature accessible by JWST for high-z galaxies. AKARI mJy Unbiased Survey of Extragalactic Sources in 5MUSES (AMUSES) intends to take advantage of AKARI capability of spectroscopy in the 2 ~ 5 μ m to provide an unbiased library of 44 sample galaxies selected from a parent sample of 5MUSES, one of Spitzer legacy projects. For these 3.6 μ m flux limited sample galaxies whose redshifts range between 0 z μ m as a star formation rate (SFR) indicator while measuring ratios between PAH features. We present preliminary results of AMUSES.
近十年来，随着红外空间望远镜技术的进步，红外波段已成为研究星系演化过程中各种性质的焦点。多环芳烃(PAHs)已成为最重要的特征之一，因为这些特征主导了星系的中红外光谱。这些多环芳烃特征为校准恒星形成速率和诊断颗粒的电离状态提供了一个很好的处理方法。然而，3.3 μ m PAH特征并没有像其他PAH特征那样被研究得那么多，因为它比其他特征更弱，并且位于斯皮策能力之外，尽管它将是JWST在高z星系中唯一可获得的PAH特征。AKARI mJy星系外星系无偏巡天(AMUSES)计划利用AKARI在2 ~ 5 μ m波段的光谱能力，从斯皮策遗留项目之一的5MUSES母星系样本中选取44个样本星系，建立一个无偏的样本星系库。在测量多环芳烃特征之间的比值时，用3.6 μ m通量受限的红移范围在0 z μ m之间的星系样本作为恒星形成率(SFR)指标。我们提出了AMUSES的初步结果。
{"title":"Introduction to AMUSES: AKARI Survey with a Window of Opportunity","authors":"Ji Hoon Kim, M. Im, Hyung Mok Lee, Myung Gyoon Lee","doi":"10.1051/EAS/1146016","DOIUrl":"https://doi.org/10.1051/EAS/1146016","url":null,"abstract":"With advancement of infrared space telescopes during the past decade, infrared wavelength regime has been a focal point to study various properties of galaxies with respect to evolution of galaxies. Polycyclic Aromatic Hydrocarbons (PAHs) have emerged as one of the most important features since these features dominate the mid-infrared spectra of galaxies. These PAH features provide a great handle to calibrate star formation rates and diagnose ionized states of grains. However, the PAH 3.3 μ m feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability, although it will be the only PAH feature accessible by JWST for high-z galaxies. AKARI mJy Unbiased Survey of Extragalactic Sources in 5MUSES (AMUSES) intends to take advantage of AKARI capability of spectroscopy in the 2 ~ 5 μ m to provide an unbiased library of 44 sample galaxies selected from a parent sample of 5MUSES, one of Spitzer legacy projects. For these 3.6 μ m flux limited sample galaxies whose redshifts range between 0 z μ m as a star formation rate (SFR) indicator while measuring ratios between PAH features. We present preliminary results of AMUSES.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133528331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A large number of galactic and extragalactic sources exhibit a mid-IR spectrum that is dominated by PAH emission. Looking at these spectra in more details reveals a strong variability in the shape/position of the observed features, depending on the observed source, or even the region within a source. In this article, we present the results of an analysis that has allowed us to decompose these spectra into components having a physical meaning. Most, if not all PAH dominated mid-IR spectra of HII regions, PDRs, protoplanetary disks, galaxies etc. can be fitted efficiently using a combination of these components. The results of these fits provide further insight in the composition of the emitting material and the local physical conditions. In the frame of the future IR space missions (JWST, SPICA), this approach can be very useful to probe the physical conditions in distant galaxies.
{"title":"The Shape of Mid-IR PAH Bands in the Universe","authors":"O. Berné, P. Pilleri, C. Joblin","doi":"10.1051/EAS/1146005","DOIUrl":"https://doi.org/10.1051/EAS/1146005","url":null,"abstract":"A large number of galactic and extragalactic sources exhibit a mid-IR spectrum that is dominated by PAH emission. Looking at these spectra in more details reveals a strong variability in the shape/position of the observed features, depending on the observed source, or even the region within a source. In this article, we present the results of an analysis that has allowed us to decompose these spectra into components having a physical meaning. Most, if not all PAH dominated mid-IR spectra of HII regions, PDRs, protoplanetary disks, galaxies etc. can be fitted efficiently using a combination of these components. The results of these fits provide further insight in the composition of the emitting material and the local physical conditions. In the frame of the future IR space missions (JWST, SPICA), this approach can be very useful to probe the physical conditions in distant galaxies.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122036554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Boersma, L. Allamandola, C. Bauschlicher, A. Ricca, J. Cami, E. Peeters, F. S. D. Armas, G. P. Saborido, A. Mattioda, D. Hudgins
Polycyclic Aromatic Hydrocarbons (PAHs) are widespread across the Universe and influence many stages of the Galactic lifecycle. The presence of PAHs has been well established and the rich mid-IR PAH spectrum is now commonly used as a probe into (inter)stellar envi- ronments. The NASA Ames PAH IR Spectroscopic Database has been key to test and refine the "PAH hypothesis". This database is a large coherent set (>600 spectra) of laboratory measured and DFT computed infrared spectra of PAHs from C10H8 to C130H28 and has been made available on the web at (http://www.astrochem.org/pahdb). With a new spectral window opening up; the far-IR, the study of PAH far-IR spectra and the quest for identifying a unique member of the interstel- lar PAH family has begun. To guide this research, the far-IR (>20 µm) spectra of different sets of PAHs are investigated using the NASA Ames PAH IR Spectroscopic Database. These sets explore the influence of size, shape, charge and composition on the far-IR PAH spectrum. The far-IR is also the domain of the so-called "drumhead" modes and other molecular vibrations involving low order bending vibrations of the car- bon skeleton as a whole. As with drums, these are molecule and shape specific and promise to be a key diagnostic for specific PAHs. Here, the sensitivity of these "drumhead" modes to size and shape is assessed by comparing the frequencies of the lowest drumhead modes of a family of circular shaped (the coronene "family") and rhombus shaped (the pyrene "family") PAH molecules. From this study, some consequences for an observing strategy are drawn.
{"title":"The NASA Ames PAH IR Spectroscopic Database and the far-IR","authors":"C. Boersma, L. Allamandola, C. Bauschlicher, A. Ricca, J. Cami, E. Peeters, F. S. D. Armas, G. P. Saborido, A. Mattioda, D. Hudgins","doi":"10.1051/EAS/1146011","DOIUrl":"https://doi.org/10.1051/EAS/1146011","url":null,"abstract":"Polycyclic Aromatic Hydrocarbons (PAHs) are widespread across the Universe and influence many stages of the Galactic lifecycle. The presence of PAHs has been well established and the rich mid-IR PAH spectrum is now commonly used as a probe into (inter)stellar envi- ronments. The NASA Ames PAH IR Spectroscopic Database has been key to test and refine the \"PAH hypothesis\". This database is a large coherent set (>600 spectra) of laboratory measured and DFT computed infrared spectra of PAHs from C10H8 to C130H28 and has been made available on the web at (http://www.astrochem.org/pahdb). With a new spectral window opening up; the far-IR, the study of PAH far-IR spectra and the quest for identifying a unique member of the interstel- lar PAH family has begun. To guide this research, the far-IR (>20 µm) spectra of different sets of PAHs are investigated using the NASA Ames PAH IR Spectroscopic Database. These sets explore the influence of size, shape, charge and composition on the far-IR PAH spectrum. The far-IR is also the domain of the so-called \"drumhead\" modes and other molecular vibrations involving low order bending vibrations of the car- bon skeleton as a whole. As with drums, these are molecule and shape specific and promise to be a key diagnostic for specific PAHs. Here, the sensitivity of these \"drumhead\" modes to size and shape is assessed by comparing the frequencies of the lowest drumhead modes of a family of circular shaped (the coronene \"family\") and rhombus shaped (the pyrene \"family\") PAH molecules. From this study, some consequences for an observing strategy are drawn.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131114108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An active carbon chemistry is observed at the border of photo-dissociation regions (PDRs), involving small hydrocarbons, poly- cyclic aromatic hydrocarbon (PAH) macromolecules and evaporating very small grains (VSGs). In this context, we aim at quantifying the physical and chemical evolution of PAHs (hydrogenation and charge states, aggregation, and complexation with heavy atoms) as a function of the local physical conditions (radiation field, temperature, density, abundances of atomic and molecular hydrogen, electrons and heavy atoms). We have developed a numerical model that follows the time dependency of the abundance and internal energy of each species. In this paper, we use this model to calculate the hydrogenation and charge states of coronene C24H12 as an interstellar PAH prototype. We take advantage of recent results on photodissociation and reaction rates and provide guidelines for future laboratory studies. Reaction rates of coronene-derived radical cations with H and H2 are found to be sufficiently constrained by experiments, whereas the absence of exper- imental data for neutral species is critical.
{"title":"Modelling the Physical and Chemical Evolution of PAHs and PAH-related Species in Astrophysical Environments","authors":"J. Montillaud, C. Joblin, D. Toublanc","doi":"10.1051/EAS/1146046","DOIUrl":"https://doi.org/10.1051/EAS/1146046","url":null,"abstract":"An active carbon chemistry is observed at the border of photo-dissociation regions (PDRs), involving small hydrocarbons, poly- cyclic aromatic hydrocarbon (PAH) macromolecules and evaporating very small grains (VSGs). In this context, we aim at quantifying the physical and chemical evolution of PAHs (hydrogenation and charge states, aggregation, and complexation with heavy atoms) as a function of the local physical conditions (radiation field, temperature, density, abundances of atomic and molecular hydrogen, electrons and heavy atoms). We have developed a numerical model that follows the time dependency of the abundance and internal energy of each species. In this paper, we use this model to calculate the hydrogenation and charge states of coronene C24H12 as an interstellar PAH prototype. We take advantage of recent results on photodissociation and reaction rates and provide guidelines for future laboratory studies. Reaction rates of coronene-derived radical cations with H and H2 are found to be sufficiently constrained by experiments, whereas the absence of exper- imental data for neutral species is critical.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"121 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114350067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Rapacioli, F. Spiegelman, Baptiste Joalland, Aude Simon, André Mirtschink, C. Joblin, J. Montillaud, Olivier Berné, Dahbia Talbi
The analysis of mid-IR emission suggests that a population of PAH-related very small grains containing a few hundreds of atoms are present in the deep regions of molecular clouds, although no specific species has been identified yet. In this review, we discuss several candidates for these grains: neutral and ionised PAH clusters and complexes of PAHs with Si atoms. The theoretical modelling of the properties of such molecular complexes or nanograins is a challenging task. We first present an overview of quantum chemistry derived models which can be efficiently used on-the-fly in extensive sampling of the potential energy surfaces, as required by structural optimization, classical molecular dynamics or Monte Carlo algorithms. From the simulations, various observables can be determined, such as the binding energies, finite temperature IR spectra, nucleation and evaporation rates. We discuss the relevance of those candidates in the molecular clouds photodissociation regions and propose constrains and perspectives for the nature and size of those very small grains.
{"title":"PAH-related Very Small Grains in Photodissociation Regions: Implications from Molecular Simulations","authors":"M. Rapacioli, F. Spiegelman, Baptiste Joalland, Aude Simon, André Mirtschink, C. Joblin, J. Montillaud, Olivier Berné, Dahbia Talbi","doi":"10.1051/EAS/1146024","DOIUrl":"https://doi.org/10.1051/EAS/1146024","url":null,"abstract":"The analysis of mid-IR emission suggests that a population of PAH-related very small grains containing a few hundreds of atoms are present in the deep regions of molecular clouds, although no specific species has been identified yet. In this review, we discuss several candidates for these grains: neutral and ionised PAH clusters and complexes of PAHs with Si atoms. The theoretical modelling of the properties of such molecular complexes or nanograins is a challenging task. We first present an overview of quantum chemistry derived models which can be efficiently used on-the-fly in extensive sampling of the potential energy surfaces, as required by structural optimization, classical molecular dynamics or Monte Carlo algorithms. From the simulations, various observables can be determined, such as the binding energies, finite temperature IR spectra, nucleation and evaporation rates. We discuss the relevance of those candidates in the molecular clouds photodissociation regions and propose constrains and perspectives for the nature and size of those very small grains.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127457937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We characterize PAH populations in 22 metal-poor blue compact dwarf galaxies (BCDs), 16 of which have an oxygen abundance 12+log(O/H) ≲ 8. This is the largest sample ever studied at such low metallicities. The relative PAH intensities of the 6.2, 7.7, 8.6 and 11.3 μ m features in these BCDs suggest a deficit of small PAH carriers, or alternatively, an excess of large ones at these low abundances.
{"title":"PAHs and the ISM in Metal-Poor Starbursts","authors":"L. Hunt, Y. Izotov, M. Sauvage, T. Thuan","doi":"10.1051/EAS/1146015","DOIUrl":"https://doi.org/10.1051/EAS/1146015","url":null,"abstract":"We characterize PAH populations in 22 metal-poor blue compact dwarf galaxies (BCDs), 16 of which have an oxygen abundance 12+log(O/H) ≲ 8. This is the largest sample ever studied at such low metallicities. The relative PAH intensities of the 6.2, 7.7, 8.6 and 11.3 μ m features in these BCDs suggest a deficit of small PAH carriers, or alternatively, an excess of large ones at these low abundances.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115134735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Thrower, L. Nilsson, B. Jørgensen, S. Baouche, R. Balog, A. Luntz, I. Stensgaard, E. Rauls, L. Hornekær
The possible role of neutral PAHs as catalysts for H2 forma- tion in the interstellar medium is investigated by a combined exper- imental and density function theory study of the superhydrogenation of coronene (C24H12). The calculations suggest efficient hydrogenation of both edge and centre sites, along with competing abstraction reac- tions to form H2 in a series of catalytic cycles. Scanning tunneling microscopy and thermal desorption measurements have been used to provide direct evidence of the formation of superhydrogenated coronene as a result of exposure to D atoms. Lower limit estimates for the cross- sections of 1.8×10 �17 ,5 .5×10 �18 and 1.1×10 �18 cm 2 for the formation of singly, doubly and triply hydrogenated coronene are derived. The results suggest that superhydrogenated PAHs may play an important role in H2 formation in the ISM.
通过对冕烯(C24H12)超氢化反应的实验和密度泛函理论相结合的研究，探讨了中性多环芳烃在星际介质中催化H2生成的可能作用。计算结果表明，在一系列催化循环中，边缘和中心位置都发生了有效的氢化反应，同时还发生了相互竞争的萃取反应，形成H2。扫描隧道显微镜和热解吸测量已经被用来提供由于暴露于D原子而形成超氢化冕烯的直接证据。推导了1.8×10′17、5 .5×10′18和1.1×10′18 cm 2形成单氢化、双氢化和三氢化冕烯截面的下限估计。结果表明，过氢化多环芳烃可能在ISM中H2的形成中起重要作用。
{"title":"Superhydrogenated PAHs: Catalytic Formation of H2","authors":"J. Thrower, L. Nilsson, B. Jørgensen, S. Baouche, R. Balog, A. Luntz, I. Stensgaard, E. Rauls, L. Hornekær","doi":"10.1051/EAS/1146047","DOIUrl":"https://doi.org/10.1051/EAS/1146047","url":null,"abstract":"The possible role of neutral PAHs as catalysts for H2 forma- tion in the interstellar medium is investigated by a combined exper- imental and density function theory study of the superhydrogenation of coronene (C24H12). The calculations suggest efficient hydrogenation of both edge and centre sites, along with competing abstraction reac- tions to form H2 in a series of catalytic cycles. Scanning tunneling microscopy and thermal desorption measurements have been used to provide direct evidence of the formation of superhydrogenated coronene as a result of exposure to D atoms. Lower limit estimates for the cross- sections of 1.8×10 �17 ,5 .5×10 �18 and 1.1×10 �18 cm 2 for the formation of singly, doubly and triply hydrogenated coronene are derived. The results suggest that superhydrogenated PAHs may play an important role in H2 formation in the ISM.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"205 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121631802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Depending on whom you ask, PAHs are either the smallest dust particles or the largest gas-phase molecules in space. Whether referred to as gas or dust, these PAHs can contain up to 20% of the total cosmic carbon abundance and as such also play an important role in the carbon chemistry of protoplanetary disks. The interpretation of PAH bands is often a complex procedure involving not only gas physics to determine their ionization stage and temperature, but also radiative transfer effects that can bury these bands in a strong thermal continuum from a population of larger dust particles. PAHs are most readily seen in the spectral energy distributions (SEDs) of disks around Herbig AeBe stars where they are photopro- cessed by the stellar radiation field. Resolved images taken in the PAH bands confirm their origin in the flaring surfaces of circumstellar disks: if the SED is consistent with a flat disk structure (less illuminated), there is little or no evidence of PAH emission. The very low detec- tion rates in the disks around T Tauri stars often require an overall lower abundance of PAHs in these disk surface as compared to that in molecular clouds. In this review, I will adress three aspects of PAHs in protoplanetary disks: (1) Do PAHs form in protoplanetary disks or do they originate from the precursor molecular cloud? (2) Is the presence of PAH features in SEDs a consequence of the disk structure or do PAHs in fact shape the disk structure? (3) How can we use PAHs as tracers of processes in protoplanetary disks?
{"title":"Evolution of PAHs in Protoplanetary Disks","authors":"I. Kamp","doi":"10.1051/eas/1146029","DOIUrl":"https://doi.org/10.1051/eas/1146029","url":null,"abstract":"Depending on whom you ask, PAHs are either the smallest dust particles or the largest gas-phase molecules in space. Whether referred to as gas or dust, these PAHs can contain up to 20% of the total cosmic carbon abundance and as such also play an important role in the carbon chemistry of protoplanetary disks. The interpretation of PAH bands is often a complex procedure involving not only gas physics to determine their ionization stage and temperature, but also radiative transfer effects that can bury these bands in a strong thermal continuum from a population of larger dust particles. PAHs are most readily seen in the spectral energy distributions (SEDs) of disks around Herbig AeBe stars where they are photopro- cessed by the stellar radiation field. Resolved images taken in the PAH bands confirm their origin in the flaring surfaces of circumstellar disks: if the SED is consistent with a flat disk structure (less illuminated), there is little or no evidence of PAH emission. The very low detec- tion rates in the disks around T Tauri stars often require an overall lower abundance of PAHs in these disk surface as compared to that in molecular clouds. In this review, I will adress three aspects of PAHs in protoplanetary disks: (1) Do PAHs form in protoplanetary disks or do they originate from the precursor molecular cloud? (2) Is the presence of PAH features in SEDs a consequence of the disk structure or do PAHs in fact shape the disk structure? (3) How can we use PAHs as tracers of processes in protoplanetary disks?","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114664613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As images and spectra from ISO and Spitzer have provided increasingly higher–fidelity representations of the mid–infrared (MIR) and Polycyclic Aromatic Hydrocarbon (PAH) emission from galaxies and galactic and extra–galactic regions, more systematic efforts have been devoted to establishing whether the emission in this wavelength region can be used as a reliable star formation rate indicator. This has also been in response to the extensive surveys of distant galaxies that have accumulated during the cold phase of the Spitzer Space Telescope. Results so far have been somewhat contradictory, reflecting the complex nature of the PAHs and of the mid–infrared–emitting dust in general. The two main problems faced when attempting to define a star formation rate indicator based on the mid–infrared emission from galaxies and star–forming regions are: (1) the strong dependence of the PAH emission on metallicity; (2) the heating of the PAH dust by evolved stellar populations unrelated to the current star formation. I review the status of the field, with a specific focus on these two problems, and will try to quantify the impact of each on calibrations of the mid–infrared emission as a star formation rate indicator.
{"title":"Polycyclic Aromatic Hydrocarbons as Star Formation Rate Indicators","authors":"D. Calzetti","doi":"10.1051/eas/1146014","DOIUrl":"https://doi.org/10.1051/eas/1146014","url":null,"abstract":"As images and spectra from ISO and Spitzer have provided increasingly higher–fidelity representations of the mid–infrared (MIR) and Polycyclic Aromatic Hydrocarbon (PAH) emission from galaxies and galactic and extra–galactic regions, more systematic efforts have been devoted to establishing whether the emission in this wavelength region can be used as a reliable star formation rate indicator. This has also been in response to the extensive surveys of distant galaxies that have accumulated during the cold phase of the Spitzer Space Telescope. Results so far have been somewhat contradictory, reflecting the complex nature of the PAHs and of the mid–infrared–emitting dust in general. The two main problems faced when attempting to define a star formation rate indicator based on the mid–infrared emission from galaxies and star–forming regions are: (1) the strong dependence of the PAH emission on metallicity; (2) the heating of the PAH dust by evolved stellar populations unrelated to the current star formation. I review the status of the field, with a specific focus on these two problems, and will try to quantify the impact of each on calibrations of the mid–infrared emission as a star formation rate indicator.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122472789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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