Tracing the Physical Conditions in Active Galactic Nuclei with Time-Dependent Chemistry

We present an extension of the code ProDiMo that allows for a modeling of processes pertinent to active galactic nuclei and to an ambient chemistry that is time dependent. We present a proof-of-concept and focus on a few astrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO and H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water is strongly suppressed and that this affects the bulk of the oxygen and carbon chemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly time-dependent, with ratios that vary over orders of magnitude for times longer than 10^4 years. Through ALMA observations this ratio can be used to probe how the narrow-line region evolves under large fluctuations in the SMBH accretion rate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also found in species such as H3O+, CO, and H2O. These reflect, respectively, time dependent effects in the ionization balance, the transient nature of the production of molecular gas, and the freeze-out/sublimation of water.Comment: Accepted for publication at the Journal of Physical Chemistry A "Oka Festschrift: Celebrating 45 Years of Astrochemistry

Extreme cosmic ray dominated regions: a new paradigm for high star formation density events in the Universe

We examine in detail the recent proposal that extreme cosmic ray dominated regions (CRDRs) characterize the interstellar medium of galaxies during events of high-density star formation, fundamentally altering its initial conditions (Papadopoulos 2010). Solving the coupled chemical and thermal state equations for dense UV-shielded gas reveals that the large CR energy densities in such systems [UCR ∼ few × (103-104) UCR, Gal] will indeed raise the minimum temperature of this phase (where the initial conditions of star formation are set) from ∼10 K (as in the Milky Way) to ∼50-100 K. Moreover in such extreme CRDRs the gas temperature remains fully decoupled from that of the dust, with Tkin≫Tdust, even at high densities [n(H2) ∼ 105-106 cm−3], quite unlike CRDRs in the Milky Way where Tk∼Tdust when n(H2) ≳ 105 cm−3. These dramatically different star formation initial conditions will (i) boost the Jeans mass of UV-shielded gas regions by factors of ∼10-100 with respect to those in quiescent or less extreme star-forming systems and (ii) ‘erase' the so-called inflection point of the effective equation of state of molecular gas. Both these effects occur across the entire density range of typical molecular clouds, and may represent a new paradigm for all high-density star formation in the Universe, with CRs as the key driving mechanism, operating efficiently even in the high dust extinction environments of compact extreme starbursts. The characteristic mass of young stars will be boosted as a result, naturally yielding a top-heavy stellar initial mass function (IMF) and a bimodal star formation mode (with the occurrence of extreme CRDRs setting the branching point). Such CRDRs will be present in Ultra-Luminous Infrared Galaxies (ULIRGs) and merger-driven gas-rich starbursts across the Universe where large amounts of molecular gas rapidly dissipate towards compact disc configurations where they fuel intense starbursts. In hierarchical galaxy formation models, CR-controlled star formation initial conditions lend a physical basis for the currently postulated bimodal IMF in merger/starburst versus quiescent/disc star-forming environments, while naturally making the integrated galactic IMFs a function of the star formation history of galaxie

Organic molecules in protoplanetary disks around TTauri and HerbigAe stars

The results of single-dish observations of low- and high-J transitions of selected molecules from protoplanetary disks around two TTauri stars (LkCa15 and TWHya) and two HerbigAe stars (HD163296 and MWC480) are reported. Simple molecules such as CO, 13CO, HCO+, CN and HCN are detected. Several lines of H2CO are found toward the TTauri star LkCa15 but not in other objects. No CH3OH has been detected down to abundances of 10E-9 - 10E-8 with respect to H2. SO and CS lines have been searched for without success. Line ratios indicate that the molecular emission arises from dense 10E6 - 10E8 cm-3 and moderately warm (T ~ 20-40K) intermediate height regions of the disk atmosphere, in accordance with predictions from models of the chemistry in disks. The abundances of most species are lower than in the envelope around the solar-mass protostar IRAS 16293-2422. Freeze-out and photodissociation are likely causes of the depletion. DCO+ is detected toward TWHya, but not in other objects. The high inferred DCO+/HCO+ ratio of ~0.035 is consistent with models of the deuterium fractionation in disks which include strong depletion of CO. The inferred ionization fraction in the intermediate height regions as deduced from HCO+ is at least 10E-11 - 10E-10, comparable to that derived for the midplane from recent H2D+ observations. (abridged abstract)Comment: Accepted for publication in A&A. 21 pages, 6 figures Tables 3, 4, 5 will only be published in the electronic version of the Journa

Detection of H_2 Pure Rotational Line Emission from the GG Tauri Binary System

We present the first detection of the low-lying pure rotational emission lines of H_2 from circumstellar disks around T Tauri stars, using the Short Wavelength Spectrometer on the Infrared Space Observatory. These lines provide a direct measure of the total amount of warm molecular gas in disks. The J = 2 → 0 S(0) line at 28.218 μm and the J = 3 → 1 S(1) line at 17.035 μm have been observed toward the double binary system GG Tau. Together with limits on the J = 5 → 3 S(3) and J = 7 → 5 S(5) lines, the data suggest the presence of gas at T_(kin) ≈ 110 ± 10 K with a mass of (3.6 ± 2.0) × 10^(-3) M_☉ (±3 σ). This amounts to ~3% of the total gas + dust mass of the circumbinary disk as imaged by millimeter interferometry, but it is larger than the estimated mass of the circumstellar disk(s). Possible origins for the warm gas seen in H_2 are discussed in terms of photon and wind-shock heating mechanisms of the circumbinary material, and comparisons with model calculations are made

Continuum and line modelling of discs around young stars. I. 300000 disc models for Herschel/GASPS

We have combined the thermo-chemical disc code ProDiMo with the Monte Carlo radiative transfer code MCFOST to calculate a grid of ~300000 circumstellar disc models, systematically varying 11 stellar, disc and dust parameters including the total disc mass, several disc shape parameters and the dust-to-gas ratio. For each model, dust continuum and line radiative transfer calculations are carried out for 29 far IR, sub-mm and mm lines of [OI], [CII], 12CO and o/p-H2O under 5 inclinations. The grid allows to study the influence of the input parameters on the observables, to make statistical predictions for different types of circumstellar discs, and to find systematic trends and correlations between the parameters, the continuum fluxes, and the line fluxes. The model grid, comprising the calculated disc temperatures and chemical structures, the computed SEDs, line fluxes and profiles, will be used in particular for the data interpretation of the Herschel open time key programme GASPS. The calculated line fluxes show a strong dependence on the assumed UV excess of the central star, and on the disc flaring. The fraction of models predicting [OI] and [CII] fine-structure lines fluxes above Herschel/PACS and Spica/SAFARI detection limits are calculated as function of disc mass. The possibility of deriving the disc gas mass from line observations is discussed.Comment: accepted by MNRAS. 5 pages, 4 figures, 3 table

Size-dependent charging of dust particles in protoplanetary disks Can turbulence cause charge separation and lightning?

Protoplanetary disk are the foundation of planet formation. Lightning can have a profound impact on the chemistry of planetary atmospheres. The emergence of lightning in a similar manner in protoplanetary disks, would substantially alter the chemistry of protoplanetary disks. We aim to study under which conditions lightning could emerge within protoplanetary disks. We employ the ProDiMo code to make 2D thermo-chemical models of protoplanetary disks. We included a new way of how the code handles dust grains, which allows the consideration of dust grains of different sizes. We investigate the chemical composition, dust charging behaviour and charge balance of these models, to determine which regions could be most sufficient for lightning. We identify 6 regions within the disks where the charge balance is dominated by different radiation processes and find that the emergence of lightning is most probable in the lower and warmer regions of the midplane. This is due to the low electron abundance ($n_{\rm e}/n_{\rm\langle H \rangle}<10^{-15}$) in these regions and dust grains being the most abundant negative charge carriers ($n_{\rm Z}/n_{\rm\langle H \rangle}> 10^{-13}$). We find that $\rm NH4^+$ is the most abundant positive charge carrier in those regions at the same abundances as the dust grains. We then develop a method of inducing electric fields via turbulence within this mix of dust grains and $\rm NH_4^+$. The electric fields generated with this mechanism are however several orders of magnitude weaker than required to overcome the critical electric field

Interferometric Observations of Formaldehyde in the Protoplanetary Disk around LkCa15

Emission from the $2_{12}-1_{11}$ line of H$_2$CO has been detected and marginally resolved toward LkCa15 by the Nobeyama Millimeter Array. The column density of H$_2$CO is higher than that observed in DM Tau and than predicted by theoretical models of disk chemistry; also the line-intensity profile is less centrally peaked than that for CO. A similar behavior is observed in other organic gaseous molecules in the LkCa 15 disk.Comment: 5 pages, 4 figures. accepted to PASJ (Publication of Astronomical Society of Japan

Tracing micron-sized grains in molecular clouds with coreshine

Recently discovered scattered light at 3-5 µm from low-mass cores (so-called "coreshine") reveals the presence of grains around 1 µm. But only a fraction of the cores investigated so far show the effect. We derive a simple limit for detecting scattered light from a low-mass core can be derived. The extinction by the core prohibits detection in bright parts of the Galactic plane, the phase function favors the off-plane detection near the Galactic center and to some extent near the Galactic anti-center. Our 3D radiative transfer calculations for the core L260 show that also the K band is capable of probing coreshine, and that the shape of the Ks band surface brightness profile limits the largest grains to sizes of to 1-1.5 µm. For the core L1506C showing coreshine and strong depletion, but low density and turbulence our grain growth calculations and radiative transfer modeling show detectable coreshine at 3.6 µm only when we increase the core density and the turbulence above what is currently observed. The grains could be part of primitive omnipresent large grain population becoming visible in the densest part of the ISM, could have been grown under the turbulent dense conditions of former cores, or in L1506C itself. In the later case, L1506C must have passed through a period of larger density and/or stronger turbulence. This would be consistent with the surprisingly strong depletion usually attributed to high column densities, and with the large-scale outward motion of the core envelope observed today

The protoplanetary disk of FT Tauri: multi-wavelength data analysis and modeling

Investigating the evolution of protoplanetary disks is crucial for our understanding of star and planet formation. Several theoretical and observational studies have been performed in the last decades to advance this knowledge. FT Tauri is a young star in the Taurus star forming region that was included in a number of spectroscopic and photometric surveys. We investigate the properties of the star, the circumstellar disk, and the accretion and ejection processes and propose a consistent gas and dust model also as a reference for future observational studies. We performed a multi-wavelength data analysis to derive the basic stellar and disk properties, as well as mass accretion/outflow rate from TNG-Dolores, WHT-Liris, NOT-Notcam, Keck-Nirspec, and Herschel-Pacs spectra. From the literature, we compiled a complete Spectral Energy Distribution. We then performed detailed disk modeling using the MCFOST and ProDiMo codes. Multi-wavelengths spectroscopic and photometric measurements were compared with the reddened predictions of the codes in order to constrain the disk properties. This object can serve as a benchmark for primordial disks with significant mass accretion rate, high gas content and typical size.Comment: 16 pages, 9 figures, accepted for publication in A&