Showing papers by "Marco Spaans published in 2008"
TL;DR: In this paper, a large observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays.
Abstract: Aims. Molecular emission lines originating in the nuclei of luminous infra-red galaxies are used to determine the physical properties of the nuclear ISM in these systems. Methods. A large observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays. Results. The observed line ratios and model predictions imply a separation of the observed systems into three groups: XDRs, UV-dominated high-density (n >= 10(5) cm(-3)) PDRs, and lower-density ( n = 10(4.5) cm-3) PDRs that are dominated by mechanical feedback. Conclusions. The division of the two types of PDRs follows naturally from the evolution of the star formation cycle of these sources, which evolves from deeply embedded young stars, resulting in high-density ( n >= 10(5) cm(-3)) PDRs, to a stage where the gas density has decreased ( n = 10(4.5) cm(-3)) and mechanical feedback from supernova shocks dominates the heating budget.
95 citations
TL;DR: In this paper, the authors present a method which extends Monte Carlo studies to situations that require a large dynamic range in particle number, where the amount of grouping is determined by the zoom factor, a free parameter that determines on which particles the computational effort is focused.
Abstract: We present a method which extends Monte Carlo studies to situations that require a large dynamic range in particle number. The underlying idea is that, in order to calculate the collisional evolution of a system, some particle interactions are more important than others and require more resolution, while the behavior of the less important, usually of smaller mass, particles can be considered collectively. In this approximation, groups of identical particles, sharing the same mass and structural parameters, operate as one unit. The amount of grouping is determined by the zoom factor?a free parameter that determines on which particles the computational effort is focused. Two methods for choosing the zoom factors are discussed: the equal-mass method, in which the groups trace the mass density of the distribution, and the distribution method, which additionally follows fluctuations in the distribution. Both methods achieve excellent correspondence with analytic solutions to the Smoluchowski coagulation equation. The grouping method is furthermore applied to simulations involving runaway kernels, where the particle interaction rate is a strong function of particle mass, and to situations that include catastrophic fragmentation. For the runaway simulations, previous predictions for the decrease of the runaway timescale with the initial number of particles $m{c N} $ --> are reconfirmed, extending $m{c N} $ --> to 10160. Astrophysical applications include modeling of dust coagulation, planetesimal accretion, and the dynamical evolution of stars in large globular clusters. The proposed method is a powerful tool to compute the evolution of any system where the particles interact through discrete events, with the particle properties characterized by structural parameters.
57 citations
TL;DR: In this article, the X-rays drive a low-metallicity ion-molecule chemistry that leads to the formation and excitation of CO and H2 in 100 K 15 and H 2 S(0) and S(1) emission that allows one to constrain ambient conditions.
Abstract: Many present-day galaxies are known to harbor supermassive, ≥106 M☉, black holes. These central black holes must have grown through accretion from less massive seeds in the early universe. The molecules CO and H2 can be used to trace this young population of accreting massive black holes through the X-ray irradiation of ambient gas. The X-rays drive a low-metallicity ion-molecule chemistry that leads to the formation and excitation of CO and H2 in 100 K 15 and H2 S(0) and S(1) emission is found that allows one to constrain ambient conditions. Comparable line strengths cannot be produced by FUV or cosmic-ray irradiation. Weak, but perhaps detectable, H+3 (2, 2) → (1, 1) emission is found and discussed. The models predict that black hole masses larger than 105 M☉ can be detected with ALMA, over a redshift range of 5-20, provided that the black holes radiate close to Eddington.
52 citations
TL;DR: In this paper, the authors present high resolution (0.4) observations of HNC J=3-2 with the SubMillimeter Array (SMA) and find luminous HNC 3-2 line emission in the western part of Arp220, centered on the western nucleus, while the eastern side of the merger shows relatively faint emission.
Abstract: We present high resolution (0."4) observations of HNC J=3-2 with the SubMillimeter Array (SMA). We find luminous HNC 3-2 line emission in the western part of Arp220, centered on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K), narrow (60 km/s) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment. We discuss this briefly in the context of an X-ray chemistry and radiative excitation. We conclude that the luminous and possibly amplified HNC emission of the western nucleus of the Arp220 merger reflects the unusual, and perhaps transient, environment of the starburst/AGN activity there. The faint HNC line emission towards Arp220-east reveals a real difference in physical conditions between the two merger nuclei.
42 citations
TL;DR: In this article, the authors combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure.
Abstract: Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure. We discuss the observability of pure rotational H2O lines with the Herschel Space Observatory, specifically the residual gas where water is mainly frozen out. We find that measuring both the line profile of the ground 110–101 ortho-H2O transition and the ratio of this line to the 312–303 and 221–212 lines can provide information on the gas-phase water between 5 and 100 AU, but not on the snow line which is expected to occur at smaller radii.
24 citations
TL;DR: In this paper, a multi-line spectroscopy in the far-infrared (FIR) was used to detect strong continuum emission and fine-structure emission lines from photo-dissociation and H ii regions.
Abstract: Context. The Galactic center region is luminous in the far-infrared (FIR), but dominant sources of this luminosity are still controversial. Aims. We investigate physical conditions of the diffuse interstellar medium in the Galactic center region by multi-line spectroscopy in the FIR. Methods. We analyze the archival data of the Galactic center region obtained with the Long-Wavelength Spectrometer on board the Infrared Space Observatory. We detect strong continuum emission and fine-structure emission lines from photo-dissociation and H ii regions, including [O i ]a nd [Cii] lines that are dominant coolants of interstellar clouds. Results. The observations show that the [C ii]/FIR ratio is systematically low whereas the [O i]/FIR ratio is almost constant toward the Galactic center region. By using a photo-dissociation region model with observed FIR parameters, we obtain radiation an effective temperature of 6600 ± 300 K in the Galactic center region, which is significantly lower than 8600 ± 500 K in the Galactic disk region. Conclusions. Dominant sources of the FIR luminosity in the Galactic center region are not likely to be young OB stars but rather cool stars, K and M giants, which implies that the current star-formation activity is rather low in the Galactic center region.
13 citations
TL;DR: In this article, the authors presented Spitzer observations with the Infrared Array Camera toward object G111 in the outer Galactic plane, located at a distance of ~3 kpc from us and ~10kpc from the Galactic center, which confirmed the suggestion that cluster-forming clumps are present throughout the Galactic plane.
Abstract: Infrared dark clouds (IRDCs) represent the earliest observed stages of clustered star formation, characterized by large column densities of cold and dense molecular material observed in silhouette against a bright background of mid-IR emission. Up to now, IRDCs were predominantly known toward the inner Galaxy where background infrared emission levels are high. We present Spitzer observations with the Infrared Array Camera toward object G111.80+0.58 (G111) in the outer Galactic plane, located at a distance of ~3 kpc from us and ~10 kpc from the Galactic center. Earlier results show that G111 is a massive, cold molecular clump very similar to IRDCs. The mid-IR Spitzer observations unambiguously detect object G111 in absorption. We have identified for the first time an IRDC in the outer Galaxy, which confirms the suggestion that cluster-forming clumps are present throughout the Galactic plane. However, against a low mid-IR background such as the outer Galaxy it takes some effort to find them.
8 citations
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TL;DR: In this paper, the authors derived a model for the high-redshift black hole population based on observed relations between the black hole mass and the host galaxy and derived the expected flux of different fine-structure lines for a similar system at higher redshift.
Abstract: We study the prospects of finding the first quasars in the universe with ALMA and JWST. For this purpose, we derive a model for the high-redshift black hole population based on observed relations between the black hole mass and the host galaxy. We re-address previous constraints from the X-ray background with particular focus on black hole luminosities below the Eddington limit as observed in many local AGN. For such luminosities, up to 20% of high-redshift black holes can be active quasars. We then discuss the observables of high-redshift black holes for ALMA and JWST by adopting NGC 1068 as a reference system. We calculate the expected flux of different fine-structure lines for a similar system at higher redshift, and provide further predictions for high-J CO lines. We discuss the expected fluxes from stellar light, the AGN continuum and the Lyman $\alpha$ line for JWST. Line fluxes observed with ALMA can be used to derive detailed properties of high-redshift sources. We suggest two observational strategies to find potential AGN at high redshift and estimate the expected number of sources, which is between 1-10 for ALMA with a field of view of $\sim(1')^2$ searching for line emission and 100-1000 for JWST with a field of view of $(2.16')^2$ searching for continuum radiation. We find that both telescopes can probe high-redshift quasars down to redshift 10 and beyond, and therefore truely detect the first quasars in the universe.
2 citations
TL;DR: The chemical analysis of the J=1–0 transition lines of HCN, HNC, and HCO+.
Abstract: High- and low-density tracer molecules have been observed in (Ultra-) Luminous Infrared Galaxies in order to initiate multi-molecule multi-transition studies to evaluate the physical and chemical environment of the nuclear medium and the ongoing nuclear activity. The data, augmented with data available in the literature, are presented in Baan et al. (2007), which also presents a first order analysis. Here, we present the chemical analysis of the J=1–0 transition lines of HCN, HNC, and HCO+.
2 citations
TL;DR: In this article, an overview of the chemical processes that occur in primordial systems under the influence of radiation, metal abundances and dust surface reactions is given, and it is found that radiative feedback effects differ for UV and X-ray photons at any metallicity.
Abstract: An overview is given of the chemical processes that occur in primordial systems under the influence of radiation, metal abundances and dust surface reactions. It is found that radiative feedback effects differ for UV and X-ray photons at any metallicity, with molecules surviving quite well under irradiation by X-rays. Starburst and AGN will therefore enjoy quite different cooling abilities for their dense molecular gas. The presence of a cool molecular phase is strongly dependent on metallicity. Strong irradiation by cosmic rays (>100x the Milky Way value) forces a large fraction of the CO gas into neutral carbon. Dust is important for H2 and HD formation, already at metallicities of 10^-4-10^-3 solar, for electron abundances below 10^-3.
1 citations
TL;DR: In this paper, the line ratios of HCN/HCO(+) and HNC/HCN discrimination between PDRs and XDRs were investigated for molecular gas that was exposed to X-rays (1-100 keV, XDR) and far-ultraviolet radiation (6-13.6 eV, PDR).
Abstract: The nuclei of active galaxies harbor massive young stars, an accreting central black hole, or both. Results are presented for molecular gas that is exposed to X-rays (1-100 keV, XDRs) and far-ultraviolet radiation (6-13.6 eV, PDRs). Particular attention is paid to species like HCN, HNC and HCO(+). Line ratios of HCN/HCO(+) and HNC/HCN discrimination between PDRs and XDRs.
TL;DR: In this paper, the authors presented Spitzer observations with the Infrared Camera Array toward object G111 in the outer Galactic Plane, located at a distance of ~3 kpc from us and ~10 kpc away from the Galactic center.
Abstract: Infrared Dark Clouds (IRDCs) represent the earliest observed stages of clustered star formation, characterized by large column densities of cold and dense molecular material observed in silhouette against a bright background of mid-IR emission. Up to now, IRDCs were predominantly known toward the inner Galaxy where background infrared emission levels are high. We present Spitzer observations with the Infrared Camera Array toward object G111.80+0.58 (G111) in the outer Galactic Plane, located at a distance of ~3 kpc from us and ~10 kpc from the Galactic center. Earlier results show that G111 is a massive, cold molecular clump very similar to IRDCs. The mid-IR Spitzer observations unambiguously detect object G111 in absorption. We have identified for the first time an IRDC in the outer Galaxy, which confirms the suggestion that cluster-forming clumps are present throughout the Galactic Plane. However, against a low mid-IR back ground such as the outer Galaxy it takes some effort to find them.
TL;DR: In this article, the authors combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure.
Abstract: Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure. We discuss the observability of pure rotational H2O lines with the Herschel Space Observatory, specifically the residual gas where water is mainly frozen out. We find that measuring both the line profile of the ground 110-101 ortho-H2O transition and the ratio of this line to the 312-303 and 221-212 line can provide information on the gas phase water between 5-100 AU, but not on the snow line which is expected to occur at smaller radii.
01 Jun 2008
TL;DR: In this paper, an overview of the chemical processes that occur in primordial systems under the influence of radiation is given, and it is found that radiative feedback effects differ for UV and X-ray photons at any metallicity, with molecules surviving quite well under irradiation by X-rays.
Abstract: An overview is given of the chemical processes that; occur in primordial systems under the influence of radiation. metal abundances and dust, surface reactions. It is found that radiative feedback effects differ for UV and X-ray photons at any metallicity, with molecules surviving quite well under irradiation by X-rays. Starburst and AGN will therefore enjoy quite different cooling abilities for their dense molecular gas. The presence of a cool molecular phase is strongly dependent on metallicity. Strong irradiation by cosmic rays (> 200 x the Milky Way value) forces a large fraction of the, CO gas into neutral carbon. Dust is important for H(2) and HD formation, already at metallicities of 10(-4) - 10(-3) solar, for electron abundances below 10(-3).
TL;DR: In this article, the authors have used SEST, JCMT, and IRAM 30 m telescopes to observe the J=1-0, J=3-2, and J=4-3 transition lines of HNC and HCN in the Seyfert 2 galaxies NGC 1068 and NGC 3079.
Abstract: What are the physical conditions in the nuclear region of Seyfert galaxies? Can we asses the predominant nuclear source of power starburst or AGN by using high density gas tracers? We have used SEST, JCMT, and IRAM 30 m telescopes to observe the J=1-0, J=3-2, and J=4-3 transition lines of HNC and HCN in the Seyfert 2 galaxies NGC 1068 and NGC 3079 We model the excitatioon conditions of these molecules based on the observed 3–2/1–0 line intensity ratios In these proceedings we show the line ratios and discuss the excitation conditions modeled We summarize our results and conclusions as follows: in NGC 1068, the emission of HNC emerges from lower ( 10^5 {cm-3}) Instead, the emission of HNC and HCN emerges from the same gas in NGC 3079 The observed HCN/HNC line ratios favor a PDR scenario rather than an XDR one However, the N(HNC)/N(HCN) column density ratios obtained for NGC 3079 can be found only in XDR environments