We map for the first time the two-dimensional H2 excitation of warm intergalactic gas in Stephan's Quintet on group-wide (50 נ35 kpc2) scales to quantify the temperature, mass, and warm H2 mass ...fraction as a function of position using Spitzer. Molecular gas temperatures are seen to rise (to T > 700 K) and the slope of the power-law density–temperature relation flattens along the main ridge of the filament, defining the region of maximum heating. We also performed MHD modeling of the excitation properties of the warm gas, to map the velocity structure and energy deposition rate of slow and fast molecular shocks. Slow magnetic shocks were required to explain the power radiated from the lowest-lying rotational states of H2, and strongly support the idea that energy cascades down to small scales and low velocities from the fast collision of NGC 7318b with group-wide gas. The highest levels of heating of the warm H2 are strongly correlated with the large-scale stirring of the medium as measured by C ii spectroscopy with Herschel. H2 is also seen associated with a separate bridge that extends toward the Seyfert nucleus in NGC 7319, from both Spitzer and CARMA CO observations. This opens up the possibility that both galaxy collisions and outflows from active galactic nuclei can turbulently heat gas on large scales in compact groups. The observations provide a laboratory for studying the effects of turbulent energy dissipation on group-wide scales, which may provide clues about the heating and cooling of gas at high z in early galaxy and protogalaxy formation.
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 N
2
H
+
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
14
N and
15
N 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
14
N- and
15
N-containing species onto grains results in enhanced
15
N:
14
N 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. Various chemical effects that bring models into better agreement with observations are considered. Thus, the observed values of
14
N
2
H
+
:N
15
NH
+
and
14
N
2
H
+
:
15
NNH
+
could be explained by different temperature dependences of the rates of dissociative recombination of these species. We also study the impact of the isotopic sensitivity of the charge-exchange reaction of N
2
with He
+
on the fractionation of ammonia and its singly deuterated analog and find significant depletion in the
15
N variants. However, these chemical processes require further experimental and theoretical investigations, especially at low temperature. These new findings, such as the depletion-driven fractionation, may also be relevant to the dense, UV-shielded regions of protoplanetary disks.
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 ~ 60 au resolution and compared ...these observations with synthetic DW predictions. We identified, in SO/SO2, a rotating flow that is wider and slower than the axial SiO jet. The broad outflow cavity seen in C34S 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 ~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 ≤50%.
Atomic and molecular line emissions from shocks may provide valuable information on the injection of mechanical energy into the interstellar medium (ISM), the generation of turbulence, and the ...processes of phase transition between the warm neutral medium (WNM) and the cold neutral medium (CNM). In this series of papers, we investigate the properties of shocks propagating in the WNM. Our objective is to identify the tracers of these shocks, use them to interpret ancillary observations of the local diffuse matter, and provide predictions for future observations. Shocks propagating in the WNM are studied using the Paris-Durham shock code, a multi-fluid model built to follow the thermodynamical and chemical structures of shock waves at steady-state in a plane-parallel geometry. The code, designed to take into account the impact of an external radiation field, is updated to treat self-irradiated shocks at intermediate ($30 < V_S < 100$ and high velocity ($V_S which emit ultraviolet (UV), extreme-ultraviolet (EUV), and X-ray photons. The couplings between the photons generated by the shock, the radiative precursor, and the shock structure are computed self-consistently using an exact radiative-transfer algorithm for line emission. The resulting code is explored over a wide range of parameters ($0.1 V_S and $0.1 B 10$ mu G), which covers the typical conditions of the WNM in the solar neighborhood. The explored physical conditions lead to the existence of a diversity of stationary magnetohydrodynamic solutions, including J-type, CJ-type, and C-type shocks. These shocks are found to naturally induce phase transition between the WNM and the CNM, provided that the postshock thermal pressure is higher than the maximum pressure of the WNM and that the maximum density allowed by magnetic compression is greater than the minimum density of the CNM. The input flux of mechanical energy is primarily reprocessed into line emissions from the X-ray to the submillimeter domain. Intermediate- and high-velocity shocks are found to generate a UV radiation field that scales as $V_S^3$ for $V_S < 100$ and as $V_S^2$ at higher velocities, and an X-ray radiation field that scales as $V_S^3$ for $V_S Both radiation fields may extend over large distances in the preshock depending on the density of the surrounding medium and the hardness of the X-ray field, which is solely driven by the shock velocity. This first paper presents the thermochemical trajectories of shocks in the WNM and their associated spectra. It corresponds to a new milestone in the development of the Paris-Durham shock code and a stepping stone for the analysis of observations that will be carried out in forthcoming works.
We present quantum dynamical calculations that describe the rotational excitation of H2O due to collisions with H atoms. We used a recent, high-accuracy potential energy surface, and solved the ...collisional dynamics with the close-coupling formalism, for total energies up to 12 000 cm-1. From these calculations, we obtained collisional rate coefficients for the first 45 energy levels of both ortho- and para-H2O and for temperatures in the range T = 5-1500 K. These rate coefficients are subsequently compared to the values previously published for the H2O/He and H2O/H2 collisional systems. It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory.
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 ~ 60 au resolution and compared ...these observations with synthetic DW predictions. We identified, in SO/SO2, a rotating flow that is wider and slower than the axial SiO jet. The broad outflow cavity seen in C34S 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 ~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 ≤50%.
Context. Extended filamentary Hα emission nebulae are a striking feature of nearby galaxy clusters but the formation mechanism of the filaments, and the processes which shape their morphology remain ...unclear. Aims. We conduct an investigation into the formation, evolution and destruction of dense gas in the centre of a simulated, Perseus-like, cluster under the influence of a spin-driven jet. The jet is powered by the supermassive black hole (SMBH) located in the cluster’s brightest cluster galaxy. We particularly study the role played by condensation of dense gas from the diffuse intracluster medium, and the impact of direct uplifting of existing dense gas by the jets, in determining the spatial distribution and kinematics of the dense gas. Methods. We present a hydrodynamical simulation of an idealised Perseus-like cluster using the adaptive mesh refinement code RAMSES. Our simulation includes a SMBH that self-consistently tracks its spin evolution via its local accretion, and in turn drives a large-scale jet whose direction is based on the black hole’s spin evolution. The simulation also includes a live dark matter (DM) halo, a SMBH free to move in the DM potential, star formation and stellar feedback. Results. We show that the formation and destruction of dense gas is closely linked to the SMBH’s feedback cycle, and that its morphology is highly variable throughout the simulation. While extended filamentary structures readily condense from the hot intra-cluster medium, they are easily shattered into an overly clumpy distribution of gas during their interaction with the jet driven outflows. Condensation occurs predominantly onto infalling gas located 5−15 kpc from the centre during quiescent phases of the central AGN, when the local ratio of the cooling time to free fall time falls below 20, i.e. when tcool/tff < 20. Conclusions. We find evidence for both condensation and uplifting of dense gas, but caution that purely hydrodynamical simulations struggle to effectively regulate the cluster cooling cycle and produce overly clumpy distributions of dense gas morphologies, compared to observation.
Context.
Recent ALMA observations suggest that the highest velocity part of molecular protostellar jets (≳80 km s
−1
) are launched from the dust-sublimation regions of the accretion disks (≲0.3 au). ...However, the formation and survival of molecules in inner protostellar disk winds, in the presence of a harsh far-ultraviolet radiation field and the absence of dust, remains unexplored.
Aims.
We aim to determine if simple molecules, such as H
2
, CO, SiO, and H
2
O, 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.
Methods.
This work is based on a recent version of 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 was then built using a parametric flow geometry. This model includes time-dependent chemistry and the attenuation of the radiation field by gas-phase photoprocesses. The influence of the mass-loss rate of the wind and of the fraction of dust on the synthesis of the molecules and on the attenuation of the radiation field is studied in detail.
Results.
We show that a small fraction of H
2
(≤10
−2
), which primarily formed through the H
−
route, can efficiently initiate molecule synthesis, such as CO and SiO above
T
K
~ 800 K. We also propose new gas-phase formation routes of H
2
that can operate in strong visible radiation fields, involving CH
+
for instance. The attenuation of the radiation field by atomic species (e.g., C, Si, and S) proceeds through continuum self-shielding. This process ensures the efficient formation of CO, OH, SiO, and H
2
O through neutral–neutral reactions and the survival of these molecules. Class 0 dust-free winds with high mass-loss rates (
Ṁ
w
≥ 2 × 10
−6
M
⊙
yr
−1
) are predicted to be rich in molecules if warm (
T
K
≥ 800 K). Interestingly, we also predict a steep decrease in the SiO-to-CO abundance ratio with the decline of mass-loss rate, from Class 0 to Class I protostars. The molecular content of disk winds is very sensitive to the presence of dust, and a mass-fraction of surviving dust as small as 10
−5
significantly increases the H
2
O and SiO abundances.
Conclusions.
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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