arXiv subjects

G. Pineau des Forêts

Publications and source records attributed to G. Pineau des Forêts.

At least 19 recordsLinked to original sources

arXiv2026

JWST imaging of the Pleiades: anisotropy of turbulence in the cold neutral medium

Interstellar medium studies rely on magnetohydrodynamic (MHD) turbulence as a framework for interpretation. In this context, the statistical characterization of interstellar observations is of prime importance. We open a new perspective on diffuse interstellar matter by analyzing James Webb Space Telescope (JWST) observations of the Pleiades nebula with NIRCam. These observations are remarkable in that they provide a microscope view at the cold neutral medium (CNM) with a spatial resolution of 0.2 mpc (40 au). A two-dimensional Fourier analysis is used to characterize the structure of PAH emission in regions near and far from the Pleiades star Merope. To produce maps of the interstellar emission, stars and galaxies are filtered out. The final step in the data cleaning involves subtracting a component, in Fourier space, which we infer to be a residual of the near-infrared cosmic background. The PAH emission power spectra are highly anisotropic. They are well fitted with a break-free power-law, suggesting that we do not observe a specific scale for energy dissipation. Power-law indices are -3.5 near Merope and -3 in the more distant field. The magnetic field orientation, as derived from the Planck dust polarization data, aligns with the PAH anisotropy. The power anisotropy is constant across scales. These findings are discussed in relation to interstellar turbulence that may be driven by the Pleiades stars. The JWST observations of the Pleiades offer a new viewpoint for comparing observations and theoretical models, as they examine physical scales at which turbulence in the CNM is subsonic and decoupled from the thermal instability. The observations may indicate that the turbulent energy cascade in the CNM is anisotropic.

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arXiv2025

Collisions in a system of conical jet/counterjet outflows

Stars predominantly form in compact, non-hierarchical clusters. The gas outflows ejected by protostars can intersect and interact with each other, resulting in complex interactions that affect the dynamics, morphology, and evolution of these outflows. Determining the probability of an encounter between them requires a Bayesian approach that considers the collimation, length (or age), and separation between young stellar objects in the clusters. In this study, we employ a Monte Carlo approach to estimate this probability as a function of the jet opening angle and the ratio between the jet length and the separation between stars. We propose a function that predicts the number of interactions within a cluster based on the opening angle of the gas outflows ejected by protostars.

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arXiv2024

Radiative and mechanical energies in galaxies I. Contributions of molecular shocks and PDRs in 3C 326 N

Context: Atomic and molecular lines in galaxies offer insights into energy budgets and feedback mechanisms. Aims: This study establishes a new framework for interpreting these lines and deducing energy budgets from observations. Methods: Atomic and molecular lines detected in a given object are assumed to result from the combination of distributions of shocks and photo-dissociation regions (PDR). Using the Paris-Durham shock code and the Meudon PDR code, emissions are computed over a wide range of parameters. Total emissions are calculated using probability distribution functions, with a defined distance metric based on observed and predicted intensity ratios. Results: We analyze the radio galaxy 3C 326 N, finding both shocks and PDRs necessary to explain the line fluxes. Viable solutions occur only at low densities ($\rm n_H < 100 cm^{-3}$), indicating emission from diffuse interstellar matter. The optimal solution involves low-velocity shocks (5-20 km/s) in PDRs illuminated by UV radiation ten times stronger than in the solar neighborhood. The H$2$ 0-0 S(0) $28 μ$m, [CII] $158 μ$m, and [OI] $63 μ$m lines originate from PDRs, while other H$2$ lines mostly come from shocks. The reprocessed radiative and mechanical energies are $\rm {L_{UV} = 6.3\times10^9 L\odot}$ and $\rm {L_K = 3.9\times10^8 L_\odot}$, respectively, in agreement with 3C 326 N's infrared luminosity, and consistent with 1% of the AGN jet kinetic power dissipated in the interstellar medium. Conclusions: This study demonstrates that the radiative and mechanical energy budgets of galaxies can be derived from observations of atomic and molecular lines alone. It highlights the unexpected importance of the diffuse medium for 3C 326 N. Comparison with new JWST data for 3C 326 N shows striking agreement, opening new prospects for predicting and interpreting extragalactic observations.

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arXiv2022

Wide-angle protostellar outflows driven by narrow jets in stratified cores

Most simulations of outflow feedback on star formation are based on the assumption that outflows are driven by a wide angle "X-wind," rather than a narrow jet. However, the arguments initially raised against pure jet-driven flows were based on steady ejection in a uniform medium, a notion that is no longer supported based on recent observations. We aim to determine whether a pulsed narrow jet launched in a density-stratified, self-gravitating core could reproduce typical molecular outflow properties, without the help of a wide-angle wind component. We performed axisymmetric hydrodynamic simulations using the MPI-AMRVAC code with optically thin radiative cooling on timescales up to 10000 yrs. Then we computed and compared the predicted properties with observational data. First, the jet-driven shell expands faster and wider through a core with steeply decreasing density than through an uniform core. Second, when blown into the same singular flattened core, a jet-driven shell has a similar width as a wide-angle wind-driven shell in the first few hundred years, but a decelerating expansion on long timescales. The flow adopts a conical shape and a base opening angle reaching up to $90\unicode{xb0}$. Third, after $\sim$ 10000 yrs, a pulsed jet-driven shell shows fitting features and a qualitative resemblance with recent observations of protostellar outflows with the Atacama Large Millimeter Array (ALMA), such as HH46-47 and CARMA-7. In particular, similarities are seen in the shell widths, opening angles, position-velocity diagrams, and mass-velocity distribution, with some showing a closer resemblance than in simulations based on a wide-angle "X-wind" model. Therefore, a realistic ambient density stratification in addition to millenia-long integration times are equally essential to reliably predict the properties of outflows driven by a pulsed jet and to confront them with the observations.

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arXiv2022

The ortho-to-para ratio of water in interstellar clouds

The nuclear-spin chemistry of interstellar water is investigated using the University of Grenoble Alpes Astrochemical Network (UGAN). This network includes reactions involving the different nuclear-spin states of the hydrides of carbon, nitrogen, oxygen and sulphur, as well as their deuterated forms. Nuclear-spin selection rules are implemented within the scrambling hypothesis for reactions involving up to seven protons. The abundances and ortho-to-para ratios (OPRs) of gas-phase water and water ions (H$_2$O$^+$ and H$_3$O$^+$) are computed under the steady-state conditions representative of a dark molecular cloud and during the early phase of gravitational collapse of a prestellar core. The model incorporates the freezing of the molecules on to grains, simple grain surface chemistry and cosmic-ray induced and direct desorption of ices. The predicted OPRs are found to deviate significantly from both thermal and statistical values and to be independent of temperature below $\sim $30~K. The OPR of H$_2$O is shown to lie between 1.5 and 2.6, depending on the spin-state of H$_2$, in good agreement with values derived in translucent clouds with relatively high extinction. In the prestellar core collapse calculations, the OPR of H$_2$O is shown to reach the statistical value of 3 in regions with severe depletion ($n_{\rm H}> 10^7$~cm$^{-3}$). We conclude that a low water OPR ($\lesssim 2.5$) is consistent with gas-phase ion-neutral chemistry and reflects a gas with OPR(H$_2)\lesssim 1$. Available OPR measurements in protoplanetary disks and comets are finally discussed.

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arXiv2021

Sulfur gas-phase abundance in dense cores

The abundance of volatile sulfur in dense clouds is long-standing problem in studies of the physics and chemistry of star-forming regions. Sulfur is an important species because its low ionization potential may possibly make it an important charge carrier. The observed sulfur-bearing species in the gas-phase of dense clouds represent only a minor fraction of the cosmic sulfur abundance, which has been interpreted as a signature of sulfur depletion into ices at the surface of dust grains. However, atomic sulfur, which could be the main gas-phase carrier, cannot be observed directly in cold cores. We present measurements of the nitrogen sulfide (NS) radical toward four dense cores performed with the IRAM-30m telescope. Analytical chemical considerations and chemical models over a wide parameter space show that the NS:N2H+ abundance ratio provides a direct constraint on the abundance of gas-phase atomic sulfur. Toward early-type cores, we find that $n(\rm S)/n_{\rm H}$ is close, or even equal, to the cosmic abundance of sulfur, 14$\times 10^{-6}$, demonstrating that sulfur is not depleted and is atomic, which is in agreement with chemical models. More chemically evolved cores show sulfur depletion by factors up to 100 in their densest parts. In L1544, atomic sulfur depletion is shown to increase with increasing density. Future observations are needed to discover the solid-phase carrier of sulfur. The initial steps of the collapse of pre-stellar cores in the high sulfur abundance regime also need to be explored from their chemical and dynamical perspectives.

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arXiv2021

Excitation mechanisms in the intracluster filaments surrounding Brightest Cluster Galaxies

The excitation of the filamentary gas structures surrounding giant elliptical galaxies at the center of cool-core clusters, a.k.a BCGs (brightest cluster galaxies), is key to our understanding of active galactic nucleus feedback, and of the impact of environmental and local effects on star formation. We investigate the contribution of the thermal radiation from the cooling flow surrounding BCGs to the excitation of the filaments. We explore the effects of small levels of extra-heating (turbulence), and of metallicity, on the optical and infrared lines. Using the Cloudy code, we model the photoionization and photodissociation of a slab of gas of optical depth AV{\leq}30mag at constant pressure, in order to calculate self-consistently all of the gas phases, from ionized gas to molecular gas. The ionizing source is the EUV and soft X-ray radiation emitted by the cooling gas. We test these models comparing their predictions to the rich multi-wavelength observations, from optical to submillimeter. These models reproduce most of the multi-wavelength spectra observed in the nebulae surrounding the BCGs, not only the LINER-like optical diagnostics: [O iii]λ 5007 Å/H\b{eta}, [N ii]λ 6583 Å/Hα and ([S ii]λ 6716 Å+[S ii]λ 6731 Å)/Hα but also the infrared emission lines from the atomic gas. The modeled ro-vib H2 lines also match observations, which indicates that near and mid-IR H2 lines are mostly excited by collisions between H2 molecules and secondary electrons produced naturally inside the cloud by the interaction between the X-rays and the cold gas in the filament. However, there is still some tension between ionized and molecular line tracers (i.e. CO), which requires to optimize the cloud structure and the density of the molecular zone.

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arXiv2020

Self-generated ultraviolet radiation in molecular shock waves I. Effects of Lyman $α$, Lyman $β$, and two-photon continuum

Shocks are ubiquitous in the interstellar and intergalactic media, where their chemical and radiative signatures reveal the physical conditions in which they arise. Detailed astrochemical models of shocks at all velocities are necessary to understand the physics of many environments including protostellar outflows, supernova remnants, and galactic outflows. We present an accurate treatment of the self-generated UV radiation in intermediate velocity, stationary, weakly magnetised, J-type, molecular shocks. Shock solutions computed with the Paris-Durham shock code are post-processed using a multi-level accelerated $Λ$-iteration radiative transfer algorithm to compute Ly$α$, Ly$β$, and 2-photon continuum emission. The subsequent impacts on the ionisation and dissociation of key atomic and molecular species as well as on the heating by the photoelectric effect take the wavelength dependent cross-sections and the fluid velocity profile into account. We analyse shock models with velocities $V=25-60$ km/s, propagating in dense ($n \geq 10^4$ ${\rm cm}^{-3}$), shielded gas. Self-absorption traps Ly$α$ photons in a small region in the shock, though a large fraction escapes into the line wings. We find a critical velocity $V\sim 30$ km/s above which shocks produce a Ly$α$ photon flux exceeding that of the standard ISRF. The escaping photons generate a warm slab (T~100 K) ahead of the shock as well as pre-ionise C and S. These shocks are traced by bright atomic fine structure (e.g. O and S) and metastable (e.g. O and C) lines, substantive molecular emission (e.g. H2, OH, and CO), enhanced column densities of several species (e.g. CH+ and HCO+), as well as a severe destruction of H2O. As much as 13-21% of the initial kinetic energy of the shock escapes in Ly$α$ and Ly$β$ photons if the dust opacity in the radiative precursor allows it.

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arXiv2020

Depletion and fractionation of nitrogen in collapsing cores

Measurements of the nitrogen isotopic ratio in Solar System comets show a constant value, ~140, which is three times lower than the protosolar ratio, a highly significant difference that remains unexplained. Observations of static starless cores at early stages of collapse confirm the theoretical expectation that nitrogen fractionation in interstellar conditions is marginal for most species. Yet, observed isotopic ratios in N2H+ are at variance with model predictions. These gaps in our understanding of how the isotopic reservoirs of nitrogen evolve, from interstellar clouds to comets, and, more generally, to protosolar nebulae, may have their origin in missing processes or misconceptions in the chemistry of interstellar nitrogen. So far, theoretical studies of nitrogen fractionation in starless cores have addressed the quasi-static phase of their evolution such that the effect of dynamical collapse on the isotopic ratio is not known. In this paper, we investigate the fractionation of 14N and 15N during the gravitational collapse of a pre-stellar core through gas-phase and grain adsorption and desorption reactions. The initial chemical conditions, which are obtained in steady state after typically a few Myr, show low degrees of fractionation in the gas phase, in agreement with earlier studies. However, during collapse, the differential rate of adsorption of 14N- and 15N-containing species onto grains results in enhanced 15N:14N ratios, in better agreement with the observations. Furthermore, we find differences in the behavior, with increasing density, of the isotopic ratio in different species. We find that the collapse must take place on approximately one free-fall timescale, based on the CO abundance profile in L183 [see the end in the PDF file]

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arXiv2020

Dust coagulation feedback on magnetohydrodynamic resistivities in protostellar collapse

The degree of coupling between the gas and the magnetic field during the collapse of a core and the subsequent formation of a disk depends on the assumed dust size distribution. We study the impact of grain-grain coagulation on the evolution of magnetohydrodynamic (MHD) resistivities during the collapse of a prestellar core. We use a 1-D model to follow the evolution of the dust size distribution, out-of-equilibrium ionization state and gas chemistry during the collapse of a prestellar core. To compute the grain-grain collisional rate, we consider models for both random and systematic, size-dependent, velocities. We include grain growth through grain-grain coagulation and ice accretion, but ignore grain fragmentation. Starting with a MRN (Mathis et al. 1977) size distribution, we find that coagulation in grain-grain collisions generated by hydrodynamical turbulence is not efficient at removing the smallest grains, and as a consequence does not affect much the evolution of the Hall and ambipolar diffusion MHD resistivities which still severly drop during the collapse like in models without coagulation. The inclusion of systematic velocities, possibly induced by the presence of ambipolar diffusion, increases the coagulation rate between small and large grains, removing small grains earlier in the collapse and therefore limiting the drop in the Hall and ambipolar diffusion resistivities. At intermediate densities ($n_{\rm H} \sim 10^8\,$cm$^{-3}$), the Hall and ambipolar diffusion resistivities are found to be higher by 1 to 2 orders of magnitude in models with coagulation than in models where coagulation is ignored, and also higher than in a toy model without coagulation where all grains smaller than $0.1\,μ$m would have been removed in the parent cloud before the collapse. When grain drift velocities induced by ambipolar diffusion are included, dust coagulation ... (abridged)

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arXiv2020

Constraining MHD disk winds with ALMA. Apparent rotation signatures and application to HH212

Large millimeter interferometers are revealing a growing number of rotating outflows, which are suggested to trace magneto-centrifugal disk winds (MHD DWs). However, their impact on disk accretion is not yet well quantified. Here we identify systematic biases in retrieving the true launch zone, magnetic lever arm, and angular momentum flux of an MHD DW from apparent rotation signatures. Synthetic position-velocity cuts are constructed from self-similar MHD DWs over a broad range of parameters, and three different methods are applied for estimating the specific angular momentum. We find that the launch radius inferred using the well-known relation from Anderson et al. (2006) can markedly differ from the true outermost launch radius $r_{out}$ of the DW. The "double-peak separation" and "flow width" methods provide only a strict lower limit to $r_{out}$. This bias is independent of angular resolution and can reach a factor ten. In contrast, the "rotation curve" method gives a good estimate of $r_{out}$ when the flow is well resolved, and an upper limit otherwise. The magnetic lever arm is always underestimated. Only comparison with synthetic predictions can take into account properly all observational effects. As an application, we present a comparison with ALMA observations of HH212 at resolutions from 250 au to 16 au, which represents the most stringent observational test of MHD DW to date. This comparison confirms our predicted biases for the double-peak separation method, and the large $r_{out}\sim40~$au and small magnetic lever arm first suggested by Tabone et al. (2017). We also derive the first accurate analytical expression for the fraction of disk angular momentum extracted by an MHD disk wind of given radial extent, magnetic lever arm, and mass flux. Application to HH212 confirms that MHD DWs are serious candidates for the steady angular momentum extraction process in young disks.

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arXiv2020

Molecule formation in dust-poor irradiated jets I. Stationary disk winds

Recent ALMA observations suggest that the highest velocity part of molecular protostellar jets are launched from the dust-sublimation regions of the accretion disks (<0.3 au). However, formation and survival of molecules in inner protostellar disk winds, in the presence of a harsh FUV radiation field and the absence of dust, remain unexplored. We aim at determining if simple molecules can be synthesized and spared in fast and collimated dust-free disk winds or if a fraction of dust is necessary to explain the observed molecular abundances. This work is based on the Paris-Durham shock code designed to model irradiated environments. Fundamental properties of the dust-free chemistry are investigated from single point models. A laminar 1D disk wind model is then built using a parametric flow geometry. This model includes time-dependent chemistry and the attenuation of the radiation field by gas-phase photoprocesses. We show that a small fraction of H2 (< 1e-2), primarily formed through the H- route, can efficiently initiate molecule synthesis such as CO and SiO above TK ~ 800 K. The attenuation of the radiation field by atomic species (eg. C, Si, S) proceeds through continuum self-shielding. This process ensures efficient formation of CO, OH, SiO, H2O through neutral-neutral reactions, and the survival of these molecules. Class 0 dust-free winds with high mass-loss rates ($\dot{M}_w >$ 2e-6 Msun/yr) are predicted to be rich in molecules if warm (TK > 800 K). The molecular content of disk winds is very sensitive to the presence of dust and a mass-fraction of surviving dust as small as 1e-5 significantly increases the H2O and SiO abundances. Chemistry of high-velocity jets is a powerful tool to probe their content in dust and uncover their launching point. Models of internal shocks are required to fully exploit the current (sub-)millimeter observations and prepare future JWST observations.

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arXiv2018

Herschel Spectroscopy of the Taffy Galaxies (UGC 12914/12915 = VV 254): Enhanced [C II] emission in the collisionally-formed bridge

Using the PACS and SPIRE spectrometers on-board Herschel, we obtained observations of the Taffy galaxies (UGC 12914/12915) and bridge. The Taffy system is believed to be the result of a face-on collision between two gas-rich galaxies, in which the stellar disks passed through each other, but the gas was dispersed into a massive H I and molecular bridge between them. Emission is detected and mapped in both galaxies and the bridge in the [C II]157.7 $μ$m and [O I]63.2 $μ$m fine-structure lines. Additionally, SPIRE FTS spectroscopy detects the [C I] $^3$P$_2$$\rightarrow$$^3$P$_1$(809.3 GHz) and [C I] $^3$P$_1$$\rightarrow$$3$P$_0$(492.2 GHz) neutral carbon lines, and weakly detects high-J CO transitions in the bridge. These results indicate that the bridge is composed of a warm multi-phase medium consistent with shock and turbulent heating. Despite low star formation rates in the bridge, the [C II] emission appears to be enhanced, reaching [C II]/FIR ratios of 3.3% in parts of the bridge. Both the [C II] and [O I] lines show broad intrinsic multi-component profiles, similar to those seen in previous CO 1-0 and H I observations. The [C II] emission shares similar line profiles with both the double-peaked H I profiles and shares a high-velocity component with single-peaked CO profiles in the bridge, suggesting that the [C II] emission originates in both the neutral and molecular phases. We show that it is feasible that a combination of turbulently heated H$_2$ and high column-density H I, resulting from the galaxy collision, is responsible for the enhanced [C II] emission.

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arXiv2018

Interaction between a pulsating jet and a surrounding disk wind. A hydrodynamical perspective

The molecular richness of fast protostellar jets within 20-100 au of their source, despite strong ultraviolet irradiation, remains a challenge for the models investigated so far. We aim to investigate the effect of interaction between a time-variable jet and a surrounding steady disk wind, to assess the possibility of jet chemical enrichement by the wind, and the characteristic signatures of such a configuration. We have constructed an analytic model of a jet bow shock driven into a surrounding slower disk wind in the thin shell approximation. The refilling of the post bow shock cavity from below by the disk wind is also studied. An extension of the model to the case of two or more successive internal working surfaces (IWS) is made. We then compared this analytic model with numerical simulations with and without a surrounding disk wind. We find that at early times (of order the variability period), jet bow shocks travel in refilled pristine disk-wind material, before interacting with the cocoon of older bow shocks. This opens the possibility of bow shock chemical enrichment (if the disk wind is molecular and dusty) and of probing the unperturbed disk wind structure near the jet base. Several distinctive signatures of the presence of a surrounding disk wind are identified, in the bow shock morphology and kinematics. Numerical simulations validate our analytical approach and further show that at large scale, the passage of many jet IWS inside a disk wind produces a stationary V-shaped cavity, closing down onto the axis at a finite distance from the source.

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arXiv2017

ALMA discovery of a rotating SO/SO$_2$ flow in HH212. A possible MHD disk wind?

We wish to constrain the possible contribution of a magnetohydrodynamic disk wind (DW) to the HH212 molecular jet. We mapped the flow base with ALMA Cycle 4 at 0.13"$\sim$ 60 au resolution and compared these observations with synthetic DW predictions. We identified, in SO/SO$_2$, a rotating flow that is wider and slower than the axial SiO jet. The broad outflow cavity seen in C$^{34}$S is not carved by a fast wide-angle wind but by this slower agent. Rotation signatures may be fitted by a DW of a moderate lever arm launched out to $\sim$ 40 au with SiO tracing dust-free streamlines from 0.05-0.3 au. Such a DW could limit the core-to-star efficiency to $\leq$50%.

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arXiv2015

Warm molecular Hydrogen at high redshift with the James Webb Space Telescope

The build-up of galaxies is regulated by a complex interplay between gravitational collapse, galaxy merging and feedback related to AGN and star formation. The energy released by these processes has to dissipate for gas to cool, condense, and form stars. How gas cools is thus a key to understand galaxy formation. \textit{Spitzer Space Telescope} infrared spectroscopy revealed a population of galaxies with weak star formation and unusually powerful H$_2$ line emission. This is a signature of turbulent dissipation, sustained by large-scale mechanical energy injection. The cooling of the multiphase interstellar medium is associated with emission in the H$_2$ lines. These results have profound consequences on our understanding of regulation of star formation, feedback and energetics of galaxy formation in general. The fact that H$_2$ lines can be strongly enhanced in high-redshift turbulent galaxies will be of great importance for the \textit{James Webb Space Telescope} observations which will unveil the role that H$_2$ plays as a cooling agent in the era of galaxy assembly.

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arXiv2015

Sulphur-bearing molecules in diffuse molecular clouds: new results from SOFIA/GREAT and the IRAM 30 m telescope

We have observed five sulphur-bearing molecules in foreground diffuse molecular clouds lying along the sight-lines to five bright continuum sources. We have used the GREAT instrument on SOFIA to observe the 1383 GHz $^2Π_{3/2} J=5/2-3/2$ transitions of SH towards the star-forming regions W31C, G29.96-0.02, G34.3+0.1, W49N and W51, detecting foreground absorption towards all five sources; and the EMIR receivers on the IRAM 30m telescope at Pico Veleta to detect the H$_2$S 1(10)-1(01), CS J=2-1 and SO 3(2)-2(1) transitions. In nine foreground absorption components detected towards these sources, the inferred column densities of the four detected molecules showed relatively constant ratios, with N(SH)/N(H$_2$S) in the range 1.1 - 3.0, N(CS)/N(H$_2$S) in the range 0.32 - 0.61, and N(SO)/N(H$_2$S) in the range 0.08 - 0.30. The observed SH/H$_2$ ratios - in the range (0.5-2.6) $\times 10^{-8}$ - indicate that SH (and other sulphur-bearing molecules) account for << 1% of the gas-phase sulphur nuclei. The observed abundances of sulphur-bearing molecules, however, greatly exceed those predicted by standard models of cold diffuse molecular clouds, providing further evidence for the enhancement of endothermic reaction rates by elevated temperatures or ion-neutral drift. We have considered the observed abundance ratios in the context of shock and turbulent dissipation region (TDR) models. Using the TDR model, we find that the turbulent energy available at large scale in the diffuse ISM is sufficient to explain the observed column densities of SH and CS. Standard shock and TDR models, however, fail to reproduce the column densities of H$_2$S and SO by a factor of about 10; more elaborate shock models - in which account is taken of the velocity drift, relative to H$_2$, of SH molecules produced by the dissociative recombination of H$_3$S$^+$ - reduce this discrepancy to a factor ~ 3.

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arXiv2014

Exceptional AGN-driven turbulence inhibits star formation in the 3C 326N radio-galaxy

We detect bright [CII]158$μ$m line emission from the radio galaxy 3C 326N at z=0.09, which shows weak star formation ($SFR<0.07$M$_{\odot}$~yr$^{-1}$) despite having strong H$_2$ line emission and $2\times 10^9$M$_{\odot}$ of molecular gas. The [CII] line is twice as strong as the 0-0S(1) 17$μ$m H$_2$ line, and both lines are much in excess what is expected from UV heating. We combine infrared Spitzer and Herschel data with gas and dust modeling to infer the gas physical conditions. The [CII] line traces 30 to 50% of the molecular gas mass, which is warm (70<T<100K) and at moderate densities $700<n_{H}<3000$cm$^{-3}$. The [CII] line is broad with a blue-shifted wing, and likely to be shaped by a combination of rotation, outflowing gas, and turbulence. It matches the near-infrared H$_2$ and the Na D optical absorption lines. If the wing is interpreted as an outflow, the mass loss rate would be larger than 20M$_{\odot}$/yr, and the depletion timescale shorter than the orbital timescale ($10^8$yr). These outflow rates may be over-estimated because the stochastic injection of turbulence on galactic scales can contribute to the skewness of the line profile and mimic outflowing gas. We argue that the dissipation of turbulence is the main heating process of this gas. Cosmic rays can also contribute to the heating but they require an average gas density larger than the observational constraints. We show that strong turbulent support maintains a high gas vertical scale height (0.3-4kpc) in the disk and can inhibit the formation of gravitationally-bound structures at all scales, offering a natural explanation for the weakness of star formation in 3C 326N. To conclude, the bright [CII] line indicates that strong AGN jet-driven turbulence may play a key role in enhancing the amount of molecular gas (positive feedback) but yet can prevent star formation on galactic scales (negative feedback).

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