Showing papers by "Marco Spaans published in 2011"

Star formation in extreme environments: the effects of cosmic rays and mechanical heating

Abstract: Context. The molecular interstellar medium in extreme environments, such as Arp 220, but also NGC 253 appears to have extremely high cosmic ray (CR) rates (10 3 −10 4 × Milky Way) and substantial mechanical heating from supernova driven turbulence. Aims. We explore the consequences of high CR rates and mechanical heating on the chemistry of the clouds. Methods. PDR model predictions are made for low, n = 10 3 , and high, n = 10 5.5 cm −3 , density clouds using well-tested chemistry and radiation transfer codes. Column densities of relevant species are discussed, and special attention is given to water-related species. Fluxes are shown for fine-structure lines of O, C + ,C , and N + , and molecular lines of CO, HCN, HNC, and HCO + . A comparison is made with an X-ray dominated region model. Results. Fine-structure lines of [CII], [CI], and [OI] are remarkably similar for different mechanical heating and CR rates, when already exposed to large amounts of UV. Both HCN and H2O abundances are boosted for very high mechanical heating rates, while ionized species are relatively unaffected. Both OH + and H2O + are enhanced for very high CR rates ζ ≥ 5 × 10 −14 s −1 . A combination of OH + , OH, H2O + ,H 2O, and H3O + traces the CR rates, and is able to distinguish between enhanced cosmic rays and X-rays.

Diffuse interstellar bands in Upper Scorpius: probing variations in the DIB spectrum due to changing environmental conditions

Abstract: Aims: We study the effects of local environmental conditions affecting the diffuse interstellar band (DIB) carriers within the Upper Scorpius subgroup of the Sco OB2 association. The aim is to reveal how the still unidentified DIB carriers respond to different physical conditions prevailing in interstellar clouds, in order to shed light on the origin of the DIB carriers. Methods: We obtained optical spectra with FEROS on the ESO 1.52 m telescope at La Silla, Chile, and measured the equivalent widths of five DIBs (at 5780, 5797, 6196, 6379, and 6613 A) as well as those of absorption lines of di-atomic molecules (CH, CH+, CN) and atoms (K i, Ca i) towards 89 targets in the direction of Upper Scorpius. We construct a simple radiative transfer and chemical network model of the diffuse interstellar medium (ISM) sheet in front of Upp Sco to infer the effective radiation field. Results: By measuring the DIB and molecular spectrum of diffuse clouds towards 89 sightlines in the Upper Scorpius region, we have obtained a valuable statistical dataset that provides information on the physical conditions that influence the band strengths of the DIBs. Both the interstellar radiation field strength, IUV, and the molecular hydrogen fraction, fH2, have been derived for 55 sightlines probing the Upp Sco ISM. We discuss the relations between DIB strengths, CH and CH+ line strengths, E(B-V), IUV, and fH2. The ratio between the 5780 and 5797 A DIBs reveals a (spatial) dependence on the local environment in terms of cloud density and exposure to the interstellar radiation field, reflecting the molecular nature of these DIB carriers. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO program 63.H-0456).Tables 1, 2, and 5, and Appendices are available in electronic form at http://www.aanda.org

X-ray impact on the protoplanetary disks around T Tauri stars

Abstract: Context. T Tauri stars have X-ray luminosities in the range LX = 10 28 − 10 32 erg s −1 . These luminosities are similar to their UV luminosities (LUV ∼ 10 30 −10 31 erg s −1 ) and therefore X-rays are expected to affect the physics and chemistry of the upper layers of their surrounding protoplanetary disks. Aims. The effects and importance of X-rays on the chemical and hydrostatic structure of protoplanetary disks are investigated, species tracing X-ray irradiation (for LX ≥ 10 29 erg s −1 ) are identified and predictions for [O i], [C ii], and [N ii] fine structure line fluxes are provided. Methods. We implemented X-ray physics and chemistry into the chemo-physical disk code ProDiMo. We include Coulomb heating and H2 ionization as heating processes and both primary and secondary ionization due to X-rays in the chemistry. Results. X-rays heat the gas causing it to expand in the optically thin surface layers. Neutral molecular species are not significantly affected in terms of their abundance and spatial distribution, but charged species such as N + ,O H + ,H 2O + ,a nd H 3O + display enhanced abundances in the disk surface. Conclusions. Coulomb heating by X-rays changes the vertical structure of the disk, yielding temperatures of ∼8000 K out to distances of 50 AU. The chemical structure is altered by the high electron abundance of the gas at the disk surface, causing an efficient ion-molecule chemistry. The products of this, OH + ,H 2O + and H3O + , are of great interest for observations of low-mass young stellar objects with the Herschel Space Observatory. Both [O i] (at 63 and 145 μm) and [C ii] (at 158 μm) fine structure emission are affected only for LX > 10 30 erg s −1 .

Interstellar Ices as Witnesses of Star Formation: Selective Deuteration of Water and Organic Molecules Unveiled

Abstract: Observations of star-forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10{sup -5}. Possible reasons for this pointed to grain surface chemistry. However, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star-forming regions, while deuterated water rarely is. In this paper, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolution as the cloud collapses to form a star. Ices start with the deposition of gas-phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H{sub 2}) yields H{sub 2}O (HDO), CO only reacts with atoms (H and D) to form H{sub 2}CO (HDCO, D{sub 2}CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star-forming regions and canmore » explain the wide spread of deuterium fractionation of water observed in these environments.« less

WATER VAPOR EMISSION REVEALS A HIGHLY OBSCURED, STAR-FORMING NUCLEAR REGION IN THE QSO HOST GALAXY APM 08279+5255 AT z = 3.9

Abstract: We present the detection of four rotational emission lines of water vapor, from energy levels E u/k = 101-454 K, in the gravitationally lensed z = 3.9 QSO host galaxy APM?08279+5255. While the lowest H2 O lines are collisionally excited in clumps of warm, dense gas (density of hydrogen nuclei , gas temperature T g ~ 105 ? 21 K), we find that the excitation of the higher lines is dominated by the intense local infrared radiation field. Since only collisionally excited emission contributes to gas cooling, we conclude that H2 O is not a significant coolant of the warm molecular gas. Our excitation model requires the radiatively excited gas to be located in an extended region of high 100 ? m opacity (?100 = 0.9 ? 0.2). Locally, such extended infrared-opaque regions are found only in the nuclei of ultraluminous infrared galaxies. We propose a model where the infrared-opaque circumnuclear cloud, which is penetrated by the X-ray radiation field of the QSO nucleus, contains clumps of massive star formation where the H2 O emission originates. The radiation pressure from the intense local infrared radiation field exceeds the thermal gas pressure by about an order of magnitude, suggesting close to Eddington-limited star formation in these clumps.

Water vapor emission reveals a highly obscured, star forming nuclear region in the QSO host galaxy APM08279+5255 at z=3.9

Abstract: We present the detection of four rotational emission lines of water vapor, from energy levels Eu/k= 101 - 454 K, in the gravitationally lensed z=3.9 QSO host galaxy APM08279+5255. While the lowest H2O lines are collisionally excited in clumps of warm, dense gas (density of hydrogen nuclei n_H=(3.1 +/- 1.2) x 10^6 cm^-3, gas temperature T_g ~ 105 +/- 21 K), we find that the excitation of the higher lines is dominated by the intense local infrared radiation field. Since only collisionally excited emission contributes to gas cooling, we conclude that H2O is not a significant coolant of the warm molecular gas. Our excitation model requires the radiatively excited gas to be located in an extended region of high 100 micron opacity (tau_100 = 0.9 +/- 0.2). Locally, such extended infrared-opaque regions are found only in the nuclei of ultraluminous infrared galaxies. We propose a model where the infrared-opaque circumnuclear cloud, which is penetrated by the X-ray radiation field of the QSO nucleus, contains clumps of massive star formation where the H2O emission originates. The radiation pressure from the intense local infrared radiation field exceeds the thermal gas pressure by about an order of magnitude, suggesting close to Eddington-limited star formation in these clumps.

Interstellar ices as witnesses of star formation: selective deuteration of water and organic molecules unveiled

Abstract: Observations of star forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10-5. Possible reasons for this pointed to grain surface chemistry. How- ever, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star forming regions, while deuterated water rarely is. In this article, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolu- tion as the cloud collapses to form a star. Ices start with the deposition of gas phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H2) yields H2O (HDO), CO only reacts with atoms (H and D) to form H2CO (HDCO, D2CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star forming regions and can explain the wide spread of deuterium fractionation of water observed in these environments.

Gas modelling in the disc of HD 163296

Abstract: We present detailed model fits to observations of the disc around the Herbig Ae star HD 163296. This well-studied object has an age of ~ 4 Myr, with evidence of a circumstellar disc extending out to ~ 540AU. We use the radiation thermo-chemical disc code ProDiMo to model the gas and dust in the circumstellar disc of HD 163296, and attempt to determine the disc properties by fitting to observational line and continuum data. These include new Herschel/PACS observations obtained as part of the open-time key program GASPS (Gas in Protoplanetary Systems), consisting of a detection of the [OI]63mic line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the 12CO 3-2, 2-1 and 13CO J=1-0 line transitions, as well as the H2 S(1) transition. We explore the effects of stellar ultraviolet variability and dust settling on the line emission, and on the derived disc properties. Our fitting efforts lead to derived gas/dust ratios in the range 9-100, depending on the assumptions made. We note that the line fluxes are sensitive in general to the degree of dust settling in the disc, with an increase in line flux for settled models. This is most pronounced in lines which are formed in the warm gas in the inner disc, but the low excitation molecular lines are also affected. This has serious implications for attempts to derive the disc gas mass from line observations. We derive fractional PAH abundances between 0.007 and 0.04 relative to ISM levels. Using a stellar and UV excess input spectrum based on a detailed analysis of observations, we find that the all observations are consistent with the previously assumed disc geometry.

The impact of Lyman α trapping on the formation of primordial objects

Abstract: Numerous cosmological simulations have been performed to study the formation of the first objects. We present the results of high-resolution 3D cosmological simulations of the formation of primordial objects using the adaptive mesh refinement code FLASH by including in an approximate manner the radiative transfer effects of Lyman alpha photons. We compare the results of a Lyman a trapping case inside gas clouds with atomic and molecular hydrogen cooling cases. The principal objective of this research is to follow the collapse of a zero metallicity halo with an effective equation of state ( that accounts for the trapping) and to explore the fate of a halo in each of the three cases, specifically the impact of thermodynamics on the fragmentation of haloes. Our results show that in the case of Lyman alpha trapping, fragmentation is halted and a massive object is formed at the centre of a halo. The temperature of the gas remains well above 10(4) K and the halo is not able to fragment to stellar masses. In the atomic cooling case, gas collapses into one or two massive clumps in contrast to the Lyman alpha trapping case. For the molecular hydrogen cooling case, gas cools efficiently and fragments. The formation of massive primordial objects is thus strongly dependent on the thermodynamics of the gas. A salient feature of our results is that for the formation of massive objects, e. g. intermediate-mass black holes, feedback effects are not required to suppress H-2 cooling, as molecular hydrogen is collisionally dissociated at temperatures higher than 10(4) K as a consequence of Lyman a trapping.

The evolution of organic matter in space

Abstract: Carbon, and molecules made from it, have already been observed in the early Universe. During cosmic time, many galaxies undergo intense periods of star formation, during which heavy elements like carbon, oxygen, nitrogen, silicon and iron are produced. Also, many complex molecules, from carbon monoxide to polycyclic aromatic hydrocarbons, are detected in these systems, like they are for our own Galaxy. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly high number of molecules that are used in contemporary biochemistry on the Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites and interplanetary dust particles. Large quantities of extra-terrestrial material were delivered via comets and asteroids to young planetary surfaces during the heavy bombardment phase. Monitoring the formation and evolution of organic matter in space is crucial in order to determine the prebiotic reservoirs available to the early Earth. It is equally important to reveal abiotic routes to prebiotic molecules in the Earth environments. Materials from both carbon sources (extra-terrestrial and endogenous) may have contributed to biochemical pathways on the Earth leading to life's origin. The research avenues discussed also guide us to extend our knowledge to other habitable worlds.

Star formation near an obscured AGN - Variations in the initial mass function

Abstract: The conditions that affect the formation of stars in radiatively and mechanically active environments are quite different from the conditions that apply to our local interstellar neighborhood. In these galactic environments, a variety of feedback processes can play a significant role in shaping the initial mass function (IMF). Here, we present a numerical study on the effects of an accreting black hole and the influence of nearby massive stars to a collapsing, 800 M-circle dot, molecular cloud at 10 pc distance from the black hole. Our work focusses on the star-forming ISM in the centers of (ultra-)luminous infrared galaxies ((U)LIRGS). We therefore assume that this region is enshrouded by gas and dust and that most of the UV and soft X-ray radiation from the broad line region (BLR) is attenuated along the line of sight to the model cloud. We then parametrize and study radiative feedback effects of hard X-rays emanating from the black hole BLR, increased cosmic ray rates caused by supernovae in starbursts, and strong UV radiation produced by nearby massive stars. We also investigate the importance of shear from the supermassive, 10(6)-10(8) M-circle dot, black hole as the star-forming cloud orbits around it. A grid of 42 models is created and calculated with the hydrodynamical code FLASH. We find that thermal pressure from X-rays compresses the cloud, which induces a high star-formation rate early on, but reduces the overall star-formation efficiency (SFE) to about 7% through gas depletion by evaporation. We see that the turn-over mass of the IMF increases up to a factor of 2.3, M-turn = 1-1.5 M-circle dot, for the model with the highest X-ray flux (160 erg s(-1) cm(-2)), while the high-mass slope of the IMF becomes Gamma greater than or similar to -1 (Gamma(Salpeter) = -1.35). This results in more high-mass stars and a non-Salpeter IMF. Cosmic rays penetrate deeply into the cloud and increase the gas temperature to about 50 K for rates that are roughly 100 times Galactic and 200 K for 3000 times Galactic, which leads to a reduced formation efficiency of low-mass stars. While the shape of the mass function is preserved, high cosmic ray rates increase the average mass of stars, thereby shifting the turn-over mass to higher values, i.e., up to several solar masses. Owing to this process, the onset of star formation is also delayed. We find that UV radiation plays only a minor role. Because UV photons cannot penetrate a dense, n >= 10(5) cm(-3), cloud deep enough, they only affect the late time accretion by heating the medium where the cloud is embedded in. When we increase the black hole mass, for a cloud that is at 10 pc distance, the turbulence caused by shearing effects reduces the SFE slightly. Furthermore, shear weakens the effect of the other parameters on the slope of the IMF as well as the turn-over mass. The run with the most massive black hole, however, causes so much shear that the hydrodynamics is completely dominated by this effect and it severely inhibits star formation. We conclude that the IMF inside active galaxies is different from the one obtained from local environments. We also find that the combined effects of X-rays, cosmic rays, UV, and shear tend to drive toward a less pronounced deviation from a Salpeter IMF.

When sticking influences H2 formation

Abstract: Aims: Because of their catalytic properties, interstellar dust grains are crucial to the formation of H2, the most abundant molecule in the Universe The formation of molecular hydrogen strongly depends on the ability of H atoms to stick on dust grains In this study we determine the sticking coefficient of H atoms chemisorbed on graphitic surfaces, and estimate its impact on the formation of H2 Methods: The sticking probability of H atoms chemisorbed onto graphitic surfaces is obtained using a mixed classical-quantum dynamics method In this, the H atom is treated quantum-mechanically and the vibrational modes of the surface are treated classically The implications of sticking for the formation of H2 are addressed by using kinetic Monte Carlo simulations that follow how atoms stick, move and associate with each other on dust surfaces of different temperature Results: In our model, molecular hydrogen forms very efficiently for dust temperatures lower than 15 K through the involvement of physisorbed H atoms At dust temperatures higher than 15 K and gas temperatures lower than 2000 K, H2 formation differs strongly if the H atoms coming from the gas phase have to cross a square barrier (usually considered in previous studies) or a barrier obtained by density functional theory (DFT) calculations to become chemisorbed The product of the sticking times efficiency can be increased by many orders of magnitude when realistic barriers are considered If graphite phonons are taken into account in the dynamics calculations, then H atoms stick better on the surface at high energies, but the overall H2 formation efficiency is only slightly affected Our results suggest that H2 formation can proceed efficiently in photon-dominated regions, X-ray dominated regions, hot cores and in the early Universe when the first dust is available

The Structure and Dynamics of An Active Galactic Nucleus Torus: CO Line Predictions for ALMA from Three-dimensional Hydrodynamical Simulations with X-ray-driven Chemistry

Abstract: Several attempts have been made to model the mass distribution and dynamical evolution of the circumnuclear gas in active galactic nuclei (AGNs). However, chemical evolution is not included in detail in three-dimensional (3D) hydrodynamic simulations. The X-ray radiation from the AGN can drive the gas chemistry and affect the thermodynamics, as well as the excitation of the interstellar medium. Therefore, we estimate the effects (on chemical abundances and excitation) of X-ray irradiation by the AGN for atomic and molecular gas in a 3D hydrodynamic model of an AGN torus.We obtain the abundances of various species from an X-ray chemical model. A 3D radiative transfer code estimates the level populations, which result in line intensity maps. Predictions for the CO J = 1 -> 0 to J = 9 -> 8 lines indicate that mid-J CO lines are excellent probes of density and dynamics in the central (less than or similar to 60 pc) region of the AGN in contrast to the low-J CO lines. Analysis of the X-CO/alpha conversion factors shows that only the higher J CO lines can be used for gas mass determination in AGN tori. The [C II] 158 mu m emission traces mostly the hot (T-k > 1000 K) central region of the AGN torus. The [C II] 158 mu m line will be useful for ALMA observations of high-redshift (z greater than or similar to 1) AGNs. The spatial scales (>= 0.25 pc) probed with our simulations match the size of the structures that ALMA will resolve in nearby (

Lyman alpha emission from the first galaxies: Implications of UV backgrounds and the formation of molecules

Abstract: The Lyman alpha line is a robust tracer of high redshift galaxies. We present estimates of Lyman alpha emission from a protogalactic halo illuminated by UV background radiation fields with various intensities. For this purpose, we performed cosmological hydrodynamics simulations with the adaptive mesh refinement code FLASH, including a detailed network for primordial chemistry, comprising the formation of primordial molecules, a multi-level model for the hydrogen atom as well as the photo-ionization and photo-dissociation processes in a UV background. We find that the presence of a background radiation field J(21) excites the emission of Lyman alpha photons, increasing the Lyman alpha luminosity up to two orders of magnitude. For a halo of similar to 10(10) M-circle dot, we find that a maximum flux of 5 x 10(-15) erg cm(-2) s(-1) is obtained for J(21) x f(esc) = 0.1, where f(esc) is the escape fraction of the ionizing radiation. Depending on the environmental conditions, the flux may vary by three orders of magnitude. For J(21) x f(esc) > 0.1 the Lyman alpha luminosity decreases as the atomic hydrogen abundance becomes rather small. The fluxes derived here can be probed using Subaru and the upcoming James Webb Space Telescope. The emission of Lyman alpha photons is extended and comes from the envelope of the halo rather than its core. In the center of the halo, line trapping becomes effective above columns of 10(22) cm(-2) and suppresses the emission of Lyman alpha. In addition, cooling by primordial molecules may decrease the gas temperature in the central region, which further reduces Lyman a emission. In the central core, H-2 is photo-dissociated for a background flux of J(21) >= 1000. For weaker radiation fields, i.e. J(21) <0.1, H-2 and HD cooling are particularly strong in the center of the halo, leading to gas temperatures as low as similar to 100 K. We also performed a parameter study with different escape fractions of ionizing photons and explored the relative role of ionizing and dissociating radiation. We find that Lyman alpha emission depends more on the strength of the ionizing background. For a constant ionizing background, the Lyman a flux increases at least by an order of magnitude for stronger photodissociation.

The Structure and Dynamics of an AGN Torus: CO Line Predictions for ALMA from 3D Hydrodynamical Simulations with X-ray Driven Chemistry

Abstract: Many efforts have been made to model the mass distribution and dynamical evolution of the circumnuclear gas in active galactic nuclei (AGNs). However, chemical evolution is not included in detail in three-dimensional (3-D) hydrodynamic simulations. The X-ray radiation from the AGN can drive the gas chemistry and affect the thermodynamics, as well as the excitation of the interstellar medium (ISM). Therefore, we estimate the effects (on chemical abundances and excitation) of X-ray irradiation by the AGN, for atomic and molecular gas in a 3-D hydrodynamic model of an AGN torus. We obtain the abundances of various species from an X-ray chemical model. A 3-D radiative transfer code estimates the level populations, which result in line intensity maps. Predictions for the CO J=1-0 to J=9-8 lines indicate that mid-J CO lines are excellent probes of density and dynamics in the central ( 1000m K) central ( 1) AGNs. The spatial scales (>0.25 pc) probed with our simulations match the size of the structures that ALMA will resolve in nearby (<45 Mpc at 0.01") galaxies.

The complexity that the first stars brought to the universe: fragility of metal-enriched gas in a radiation field

Abstract: The initial mass function (IMF) of the first (Population III) stars and Population II (Pop II) stars is poorly known due to a lack of observations of the period between recombination and reionization. In simulations of the formation of the first stars, it has been shown that, due to the limited ability of metal-free primordial gas to cool, the IMF of the first stars is a few orders of magnitude more massive than the current IMF. The transition from a high-mass IMF of the first stars to a lower-mass current IMF is thus important to understand. To study the underlying physics of this transition, we performed several simulations using the cosmological hydrodynamic adaptive mesh refinement code Enzo for metallicities of 10–4, 10–3, 10–2, and 10–1 Z ☉. In our simulations, we include a star formation prescription that is derived from a metallicity-dependent multi-phase interstellar medium (ISM) structure, an external UV radiation field, and a mechanical feedback algorithm. We also implement cosmic ray heating, photoelectric heating, and gas-dust heating/cooling, and follow the metal enrichment of the ISM. It is found that the interplay between metallicity and UV radiation leads to the coexistence of Pop III and Pop II star formation in non-zero-metallicity (Z/Z ☉ ≥ 10–2) gas. A cold (T 10–22 g cm–3) gas phase is fragile to ambient UV radiation. In a metal-poor (Z/Z ☉ ≤ 10–3) gas, the cold and dense gas phase does not form in the presence of a radiation field of F 0 ~ 10–5-10–4 erg cm–2 s–1. Therefore, metallicity by itself is not a good indicator of the Pop III-Pop II transition. Metal-rich (Z/Z ☉ ≥ 10–2) gas dynamically evolves two to three orders of magnitude faster than metal-poor gas (Z/Z ☉ ≤ 10–3). The simulations including supernova explosions show that pre-enrichment of the halo does not affect the mixing of metals.

Lyman α emission from the first galaxies : Signatures of accretion and infall in the presence of line trapping

Abstract: The formation of the first galaxies is accompanied by large accretion flows and virialization shocks, during which the gas is shock heated to temperatures of similar to 10(4) K, leading to potentially strong fluxes in the Lyman alpha line. Indeed, a number of Lyman alpha blobs have been detected at high redshift. In this Letter, we explore the origin of such Lyman alpha emission using cosmological hydrodynamical simulations that include a detailed model of atomic hydrogen as a multi-level atom and the effects of line trapping with the adaptive mesh refinement code FLASH. We see that baryons fall into the centre of a halo through cold streams of gas, giving rise to a Lyman alpha luminosity of at least 10(44) erg s(-1) at z = 4.7, similar to the observed Lyman alpha blobs. We find that a Lyman alpha flux of 5.0 x 10(-17) erg cm(-2) s(-1) emerges from the envelope of the halo rather than its centre, where the photons are efficiently trapped. Such emission can be probed in detail with the upcoming James Webb Space Telescope (JWST) and will constitute an important probe of gas infall and accretion.

The deeply obscured AGN of NGC4945 I. Spitzer-IRS maps of [Ne V], [Ne II], H2 0-0 S(1), S(2), and other tracers

Abstract: The nearly edge-on galaxy NGC4945 is one of the closest galaxies where an AGN and starburst coexist, and is one of the brightest sources at 100 keV. Near and mid-infrared spectroscopy have shown very strong obscuration of its central region, rivaled only in strength by some of the most deeply obscured ULIRGs. We aim to determine the spatial distribution of ISM features in the central 426x426 pc^2 of NGC4945. We map the central region of NGC4945 in three Spitzer-IRS modules (SH, SL and LL). We produce maps of the flux distribution of the starburst tracers [Ne II], [Ne III], [S III] and [S IV] at 12.81, 15.56, 18.71 and 10.51 mum, respectively, and a map of the AGN narrow-line region tracer [Ne V] at 14.32 mum. We also mapped the S(1), S(2) and S(3) pure rotational lines of H2, which trace the distribution of warm molecular hydrogen. We obtained an extinction map (A_V) based on the apparent strength of the 9.7 mum silicate absorption feature. Our A_V map traces the contours of the starburst ring but the highest extinction (A_V(9.85 mum)~60) is found at the nucleus. Within the uncertainty of the astrometry all emission lines are found to peak on the nucleus, except for the warm molecular hydrogen emission which shows a maximum 60-100 pc NW of the nucleus. We favour a scenario in which the lower H2 0-0 S(1) and S(2) rotational lines originate mainly from an unobscured extra-nuclear component associated with the super-wind cone observed in the HST NICMOS map of the H2 1-0 S(1) vibrational line. For the [Ne V] emission we infer an attenuation of a factor 12-160 (A_V=55-112) based on a comparison of the ratio of our [Ne V] flux and the absorption-corrected 14-195 keV Swift-BAT flux to the average [Ne V]/BAT ratio for Seyfert 1 nuclei. The high attenuation indicates that [Ne V] and [O IV] cannot be used as extinction-free tracers of AGN power in galaxies with deeply buried nuclei.

The deeply obscured AGN of NGC 4945. I. Spitzer-IRS maps of [Ne V], [Ne II], H2 0-0 S(1), S(2), and other tracers

Abstract: Context. The nearly edge-on galaxy NGC 4945 is one of the closest galaxies where an AGN and starburst coexist, and is one of the brightest sources at 100 keV. Near and mid-infrared spectroscopy have shown very strong obscuration of its central region, rivaled only in strength by some of the most deeply obscured ULIRGs. Aims: We determine the spatial distribution of ISM emission features in the central 426 × 426 pc2 of NGC 4945. Methods: We mapped the central region of NGC 4945 in three of the four Spitzer-IRS modules (SH, SL and LL). In particular, we produced maps of the flux distribution of the starburst tracers [Ne II], [Ne III], [S III] and [S IV] at 12.81, 15.56, 18.71, and 10.51 μm, respectively, and a map of the AGN narrow-line region tracer [Ne V] at 14.32 μm. In addition, we mapped the S(1), S(2), and S(3) pure rotational lines of H2, which trace the distribution of warm molecular hydrogen. Finally, we obtained an extinction map (AV) based on the apparent strength of the 9.7 μm silicate absorption feature. Results: At a spatial resolution of ~5'', our extinction map traces the contours of the starburst ring. The highest extinction is, however, found at the nucleus, where we measure AV(9.85 μm) ≈ 60. Within the uncertainty of the astrometry, all emission lines are found to peak on the nucleus, except for the warm molecular hydrogen emission, which shows a maximum 60-100 pc NW of the nucleus. We favor a scenario in which the emission of the lower H2 0-0 S(1) and S(2) rotational lines originate mainly in an unobscured extranuclear component associated with the super-wind cone observed in the HST NICMOS map of the H2 1-0 S(1) vibrational line. For the [Ne V] emission we infer an attenuation of a factor 12-160 (AV = 55-112) based on a comparison of the ratio of our [Ne V] flux and the absorption-corrected 14-195 keV Swift-BAT flux to the average [Ne V]/BAT ratio for Seyfert 1 nuclei. The high attenuation indicates that [Ne V] and [O IV] cannot be used as extinction-free tracers of AGN power in galaxies with deeply buried nuclei. We dedicate this paper to the memory of our esteemed colleague and advisor, Alan Moorwood (1945-2011), who pioneered the infrared spectroscopic study of NGC 4945. This work is based on observations obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.

The JCMT Spectral Legacy Survey: Physical structure of the molecular envelope of the high-mass protostar AFGL2591

Abstract: Context. The understanding of the formation process of massive stars (greater than or similar to 8 M-circle dot) is limited by a combination of theoretical complications and observational challenges. The high UV luminosities of massive stars give rise to chemical complexity in their natal molecular clouds and affect the dynamical properties of their circumstellar envelopes. Aims. We investigate the physical structure of the large-scale (similar to 10(4)-10(5) AU) molecular envelope of the high-mass protostar AFGL2591. Methods. Observational constraints are provided by spectral imaging in the 330-373 GHz regime from the JCMT Spectral Legacy Survey and its high-frequency extension. While the majority of the similar to 160 spectral features from the survey cube are spatially unresolved, this paper uses the 35 that are significantly extended in the spatial directions. For these features we present integrated intensity maps and velocity maps. The observed spatial distributions of a selection of six species are compared with radiative transfer models based on (i) a static spherically symmetric structure; (ii) a dynamic spherical structure; and (iii) a static flattened structure. Results. The maps of CO and its isotopic variations exhibit elongated geometries on scales of similar to 100 '', and smaller scale substructure is found in maps of N2H+, o-H2CO, CS, SO2, C2H, and various CH3OH lines. In addition, a line-of-sight velocity gradient is apparent in maps of all molecular lines presented here, except SO, SO2, and H2CO. We find two emission peaks in warm (E-up similar to 200 K) CH3OH separated by 12 '' (12 000 AU), indicative of a secondary heating source in the envelope. The spherical models are able to explain the distribution of emission for the optically thin (HCO+)-C-13 and (CS)-S-34, but not for the optically thick HCN, HCO+, and CS or for the optically thin (CO)-O-17. The introduction of velocity structure mitigates the optical depth effects, but does not fully explain the observations, especially in the spectral dimension. A static flattened envelope viewed at a small inclination angle does slightly better. Conclusions. Based on radiative transfer modeling, we conclude that a geometry of the envelope other than an isotropic static sphere is needed to circumvent line optical depth effects. We propose that this could be achieved in circumstellar envelope models with an outflow cavity and/or an inhomogeneous structure on scales less than or similar to 10(4) AU. The picture of inhomogeneity is supported by substructure observed in at least six different species.

Star formation near an obscured AGN: Variations in the initial mass function

Abstract: The conditions that affect the formation of stars in radiatively and mechanically active environments are quite different than the conditions that apply to our local interstellar neighborhood. In such galactic environments, a variety of feedback processes can play a significant role in shaping the initial mass function (IMF). Here, we present a numerical study on the effects of an accreting black hole and the influence of nearby massive stars to a collapsing, 800 M_sun, molecular cloud at 10 pc distance from the black hole. We parametrize and study radiative feedback effects of hard X-rays emanating from the black hole broad line region, increased cosmic ray rates due to supernovae in starbursts, and strong UV radiation produced by nearby massive stars. We also investigate the importance of shear from the supermassive, 10^6-10^8 M_sun, black hole as the star-forming cloud orbits around it. We find that thermal pressure from X-rays compresses the cloud, which induces a high star formation rate early on, but reduces the overall star formation efficiency to about 7% due to gas depletion by evaporation. We see that the turn-over mass of the IMF increases up to a factor of 2.3, M_turn = 1-1.5 M_sun, for the model with the highest X-ray flux (160 erg s^-1 cm^-2), while the high-mass slope of the IMF becomes Gamma > -1. This results in more high mass stars and a non-Salpeter IMF. Cosmic rays penetrate deeply into the cloud and increase the gas temperature (50-200 K), which leads to a reduced formation efficiency of low mass stars. High cosmic ray rates increase the average mass of stars, thereby shifting the turn-over mass to higher values, i.e., up to several solar masses. Due to this process, the onset of star formation is also delayed. We conclude that the IMF inside active galaxies is different than the one obtained from local environments.

First Results of the Sideband-Separating Mixer for ALMA Band 9 Upgrade

Abstract: Last year, the design and implementation details of a new modular sideband-separating mixer block, intended as an upgrade for the current single-ended ALMA Band 9 mixers, were presented at this conference. In high-frequency observation bands like ALMA Band 9 (600-720 GHz), which is strongly influenced by atmospheric noise, employment of sideband separating mixers can reduce, by roughly a factor of two, the integration time needed to reach a certain signal-to-noise ratio for spectral line observations. Alternatively, in the same integration time, a sufficiently larger selection of sources can be accessed. Two prototype mixer blocks were produced on a micro milling machine, and equipped with production Band 9 SIS mixer devices that have independently been tested in double-sideband mode. Here, we present the results of the first measurements, notably, the noise temperature, image rejection, LO pumping balance and IF response. We also present in detail a procedure of the image rejection ratio measurement, which is fast and can be used for single sideband mixers, so that a second IF chain is not required.

Lyman alpha emission from the first galaxies: Implications of UV backgrounds and the formation of molecules

Abstract: The Lyman alpha line is a robust tracer of high redshift galaxies. We present estimates of Lyman alpha emission from a protogalactic halo illuminated by UV background radiation fields with various intensities. For this purpose, we performed cosmological hydrodynamics simulations with the adaptive mesh refinement code FLASH, including a detailed network for primordial chemistry,comprising the formation of primordial molecules, a multi-level model for the hydrogen atom as well as the photo-ionization and photo-dissociation processes in a UV background. We find that the presence of a background radiation field J_21 excites the emission of Lyman alpha photons, increasing the Lyman alpha luminosity up to two orders of magnitude. For a halo of \sim 10^10 M_sun, we find that a maximum flux of 5 \times 10^-15 erg cm^-2 s^-1 is obtained for J21 \times f_esc = 0.1, where f_esc is the escape fraction of the ionizing radiation. Depending on the environmental conditions, the flux may vary by three orders of magnitude. For J_21 \times f_esc > 0.1 the Lyman alpha luminosity decreases as the atomic hydrogen abundance becomes rather small. The fluxes derived here can be probed using Subaru and the upcoming James Webb Space Telescope. The emission of Lyman alpha photons is extended and comes from the envelope of the halo rather than its core. In the center of the halo, line trapping becomes effective above columns of 10^22 cm^-2 and suppresses the emission of Lyman alpha. In addition, cooling by primordial molecules may decrease the gas temperature in the central region, which further reduces Lyman alpha emission. In the central core, H_2 is photo-dissociated for a background flux of J_21 \geq 1000. For weaker radiation fields, i.e. J_21 < 0.1, H_2 and HD cooling are particularly strong in the center of the halo, leading to gas temperatures as low as \sim 100 K.

When sticking influences H2 formation

Abstract: Aims. Interstellar dust grains, because of their catalytic properties, are crucial to the formation of H2, the most abundant molecule in the Universe. The formation of molecular hydrogen strongly depends on the ability of H atoms to stick on dust grains. In this study we determine the sticking coefficient of H atoms chemisorbed on graphitic surfaces, and estimate its impact on the forma- tion of H2. Methods. The sticking probability of H atoms chemisorbed onto graphitic surfaces is obtained using a mixed classical-quantum dynamics method. In this, the H atom is treated quantum- mechanically and the vibrational modes of the surface are treated classically. The implications of sticking for the formation of H2 are addressed by using Kinetic Monte Carlo simulations that follow how atoms stick, move and associate with each other on dust surfaces of different temper- ature. Results. In our model, molecular hydrogen forms very efficiently for dust temperatures lower than 15 K through the involvement of physisorbed H atoms. At dust temperatures higher than 15 K and gas temperatures lower than 2000 K, H2 formation differs strongly if the H atoms com- ing from the gas phase have to cross a square barrier (usually considered in previous studies) or a barrier obtained by DFT calculations to become chemisorbed. The product of sticking times efficiency can be increased by many orders of magnitude when realistic barriers are considered. If graphite phonons are taken into account in the dynamics calculations, then H atoms stick better on the surface at high energies, but the overall H2 formation efficiency is only slightly affected. Our results suggest that H2 formation can proceed efficiently in photon dominated regions, X-ray dominated regions, hot cores and in the early Universe when the first dust is available.

The complexity that the first stars brought to the Universe: Fragility of metal enriched gas in a radiation field

Abstract: The initial mass function (IMF) of the first (Population III) stars and Population II (Pop II) stars is poorly known due to a lack of observations of the period between recombination and reionization. In simulations of the formation of the first stars, it has been shown that, due to the limited ability of metal-free primordial gas to cool, the IMF of the first stars is a few orders of magnitude more massive than the current IMF. The transition from a high-mass IMF of the first stars to a lower-mass current IMF is thus important to understand. To study the underlying physics of this transition, we performed several simulations using the cosmological hydrodynamic adaptive mesh refinement code Enzo for metallicities of 10^{-4}, 10^{-3}, 10^{-2}, and 10^{-1} Z_{\odot}. In our simulations we include a star formation prescription that is derived from a metallicity dependent multi-phase ISM structure, an external UV radiation field, and a mechanical feedback algorithm. We also implement cosmic ray heating, photoelectric heating and gas-dust heating/cooling, and follow the metal enrichment of the ISM. It is found that the interplay between metallicity and UV radiation leads to the co-existence of Pop III and Pop II star formation in non-zero metallicity (Z/Z_{\odot} \geq10^{-2}) gas. A cold (T 10^{-22} g cm^{-3}) gas phase is fragile to ambient UV radiation. In a metal-poor (Z/Z_{\odot} \leq10^{-3}) gas, the cold and dense gas phase does not form in the presence of a radiation field of F_{0}\sim10^{-5}-10^{-4} erg cm^{-2} s^{-1}. Therefore, metallicity by itself is not a good indicator of the Pop III-Pop II transition. Metal-rich (Z/Z_{\odot}\geq10^{-2}) gas dynamically evolves two to three orders of magnitude faster than metal poor gas (Z/Z_{\odot}\leq10^{-3}). The simulations including SNe show that pre-enrichment of the halo does not affect the mixing of metals.

Magnetic fields during primordial star formation

Abstract: Recent FERMI observations provide a lower limit of 10^{-15} G for the magnetic field strength in the intergalactic medium (IGM) This is consistent with theoretical expectations based on the Biermann battery effect, which predicts such IGM fields already at redshifts z~10 During gravitational collapse, such magnetic fields can be amplified by compression and by turbulence, giving rise to the small-scale dynamo On scales below the Jeans length, the eddy turnover timescale is much shorter than the free-fall timescale, so that saturation can be reached during collapse This scenario has been tested and confirmed with magneto-hydrodynamical simulations following the collapse of a turbulent, weakly magnetized cloud Based on a spectral analysis, we confirm that turbulence is injected on the Jeans scale For the power spectrum of the magnetic field, we obtain the Kazantsev slope which is characteristic for the small-scale dynamo A calculation of the critical length scales for ambipolar diffusion and Ohmic dissipation shows that these scales are always small enough to allow significant amplification of the magnetic field by small-scale eddies We discuss potential implications for the protostellar accretion disk, with particular focus on the magneto-rotational instability, which may change the morphology of the disk and reduce the accretion rate by a factor of a few

The deeply obscured AGN of NGC 4945

Abstract: Context The nearly edge-on galaxy NGC 4945 is one of the closest galaxies where an AGN and starburst coexist, and is one of the brightest sources at 100 keV Near and mid-infrared spectroscopy have shown very strong obscuration of its central region, rivaled only in strength by some of the most deeply obscured ULIRGs Aims We determine the spatial distribution of ISM emission features in the central 426 × 426 pc 2 of NGC 4945 Methods We mapped the central region of NGC 4945 in three of the four Spitzer-IRS modules (SH, SL and LL) In particular, we produced maps of the flux distribution of the starburst tracers [Ne II], [Ne III], [S III] and [S IV] at 1281, 1556, 1871, and 1051 μm, respectively, and a map of the AGN narrow-line region tracer [Ne V] at 1432 μm In addition, we mapped the S(1), S(2), and S(3) pure rotational lines of H2, which trace the distribution of warm molecular hydrogen Finally, we obtained an extinction map (AV) based on the apparent strength of the 97 μm silicate absorption feature Results At a spatial resolution of ∼5 �� , our extinction map traces the contours of the starburst ring The highest extinction is, however, found at the nucleus, where we measure AV(985 μm) ≈ 60 Within the uncertainty of the astrometry, all emission lines are found to peak on the nucleus, except for the warm molecular hydrogen emission, which shows a maximum 60−100 pc NW of the nucleus We favor a scenario in which the emission of the lower H2 0−0 S(1) and S(2) rotational lines originate mainly in an unobscured extranuclear component associated with the super-wind cone observed in the HST NICMOS map of the H2 1−0 S(1) vibrational line For the [Ne V] emission we infer an attenuation of a factor 12−160 (AV = 55−112) based on a comparison of the ratio of our [Ne V] flux and the absorption-corrected 14–195 keV Swift-BAT flux to the average [Ne V]/BAT ratio for Seyfert 1 nuclei The high attenuation indicates that [Ne V] and [O IV] cannot be used as extinction-free tracers of AGN power in galaxies with deeply buried nuclei

The JCMT Spectral Legacy Survey: physical structure of the molecular envelope of the high-mass protostar AFGL2591

Abstract: The understanding of the formation process of massive stars (>8 Msun) is limited, due to theoretical complications and observational challenges. We investigate the physical structure of the large-scale (~10^4-10^5 AU) molecular envelope of the high-mass protostar AFGL2591 using spectral imaging in the 330-373 GHz regime from the JCMT Spectral Legacy Survey. Out of ~160 spectral features, this paper uses the 35 that are spatially resolved. The observed spatial distributions of a selection of six species are compared with radiative transfer models based on a static spherically symmetric structure, a dynamic spherical structure, and a static flattened structure. The maps of CO and its isotopic variations exhibit elongated geometries on scales of ~100", and smaller scale substructure is found in maps of N2H+, o-H2CO, CS, SO2, CCH, and methanol lines. A velocity gradient is apparent in maps of all molecular lines presented here, except SO, SO2, and H2CO. We find two emission peaks in warm (Eup~200K) methanol separated by 12", indicative of a secondary heating source in the envelope. The spherical models are able to explain the distribution of emission for the optically thin H13CO+ and C34S, but not for the optically thick HCN, HCO+, and CS, nor for the optically thin C17O. The introduction of velocity structure mitigates the optical depth effects, but does not fully explain the observations, especially in the spectral dimension. A static flattened envelope viewed at a small inclination angle does slightly better. We conclude that a geometry of the envelope other than an isotropic static sphere is needed to circumvent line optical depth effects. We propose that this could be achieved in envelope models with an outflow cavity and/or inhomogeneous structure at scales smaller than ~10^4 AU. The picture of inhomogeneity is supported by observed substructure in at least six species.