A magnetohydrodynamic model of a steady, transverse C-type shock in a dense molecular cloud is presented. A complete gas-grain chemical network is taken into account: the gas-phase chemistry, the adsorption of gas species on dust grains, various desorption mechanisms, the grain surface chemistry, the ion neutralization on dust grains, the sputtering of grain mantles. The population densities of energy levels of ions CI, CII and OI and molecules H$_2$, CO, H$_2$O are computed in parallel with the dynamical and chemical rate equations. The large velocity gradient approximation is used in the line radiative transfer calculations. The simulations consist of two steps: (i) modelling of the chemical and thermal evolution of a static molecular cloud and (ii) shock simulations. A comparison is made with the results of publicly available models of similar physical systems.
The focus of the paper is on the chemical processing of gas material and ice mantles of dust grains by the shock. Sputtering of ice mantles takes place in the shock region close to the temperature peak of the neutral gas. At high shock speeds, molecules ejected from ice mantles are effectively destroyed in hot gas, and their survival time is low - of the order of dozens of years. After a passage of high-speed C-type shock, a zone of high abundance of atomic hydrogen appears in the cooling postshock gas that triggers formation of complex organic species such as methanol. It is shown that abundances of some complex organic molecules (COMs) in the postshock region can be much higher than in the preshock gas. These results are important for interpretation of observations of COMs in protostellar outflows.
From integral field data we extract the optical spectra of 20 shocked clouds in the supernova remnant N132D in the Large Magellanic Cloud (LMC). Using self-consistent shock modelling, we derive the shock velocity, pre-shock cloud density and shock ram pressure in these clouds. We show that the [Fe X] and [Fe XIV] emission arises in faster, partially radiative shocks moving through the lower density gas near the periphery of the clouds. In these shocks dust has been effectively destroyed, while in the slower cloud shocks the dust destruction is incomplete until the recombination zone of the sho…
Using the adaptive mesh refinement code MG, we perform 3D hydrodynamic simulations of a supernova-cloud interaction in the "large cloud regime". The cloud is initially atomic and evolving due to the thermal instability (TI) and gravity. We study interactions in a "pre-TI" and "post-TI" stage when cold and dense clumps are present, and compare these results to idealised shock-cloud scenarios in the "small cloud regime", and a scenario without shocks. On aggregate, the supernova disruption is significantly weaker than that from an idealised shock due to the supernova impact being instantaneous, …
Star formation can be triggered by compression from shock waves. In this study, we investigated the interaction of hydrodynamic shocks with Bonnor-Ebert spheres using 3D hydrodynamical simulations with self-gravity. Our simulations indicated that the cloud evolution primarily depends on two parameters: the shock speed and initial cloud radius. The stronger shock can compress the cloud more efficiently, and when the central region becomes gravitationally unstable, a shock triggers the cloud contraction. However, if it is excessively strong, it shreds the cloud more violently and the cloud is de…
The similarities, or otherwise, of a shock or wind interacting with a cloud of density contras t$ χ= 10$ were explored in a previous paper. Here, we investigate such interactions with clouds of higher density contrast. We compare the adiabatic hydrodynamic interaction of a Mach 10 shock with a spherical cloud of $χ= 10^{3}$ with that of a cloud embedded in a wind with identical parameters to the post-shock flow. We find that initially there are only minor morphological differences between the shock-cloud and wind-cloud interactions, compared to when $χ= 10$. However, once the transmitted shock…
The diffuse interstellar medium is dynamic, and its chemistry and evolution is determined by shock fronts as well as photodissociation. Shocks are implied by the supersonic motions and velocity dispersion often statistically called "turbulence". We compare models of magnetohydrodynamic (MHD) shocks, with speeds typical of cloud motions through the ISM (3-25 km/s) and densities typical of cold neutral gas (~ 100 cm-3), to archival observations of the atomic hydrogen 21-cm line for gas kinematics, far-infrared emission for dust mass, and mid-infrared emission for high-resolution morphology, to i…
Using the adaptive mesh refinement code MG, we perform hydrodynamic simulations of the interaction of a shock with a molecular cloud evolving due to thermal instability and gravity. To explore the relative importance of these processes, three case studies are presented. The first follows the formation of a molecular cloud out of an initially quiescent atomic medium due to the effects of thermal instability and gravity. The second case introduces a shock whilst the cloud is still in the warm atomic phase, and the third scenario introduces a shock once the molecular cloud has formed. The shocks …
We report three-dimensional hydrodynamical simulations of shocks (${\cal M_{\rm shock}}\geq 4$) interacting with fractal multicloud layers. The evolution of shock-multicloud systems consists of four stages: a shock-splitting phase in which reflected and refracted shocks are generated, a compression phase in which the forward shock compresses cloud material, an expansion phase triggered by internal heating and shock re-acceleration, and a mixing phase in which shear instabilities generate turbulence. We compare multicloud layers with narrow ($σ_ρ=1.9\barρ$) and wide ($σ_ρ=5.9\barρ$) log-normal …
We compare the properties of shocked gas in Sgr B2 with maps obtained from 3D simulations of a collision between two fractal clouds. In agreement with $^{13}$CO(1-0) observations, our simulations show that a cloud-cloud collision produces a region with a highly turbulent density substructure with an average $N_{\rm H2}\gtrsim 5\times10^{22}\,\rm cm^{-2}$. Similarly, our numerical multi-channel shock study shows that colliding clouds are efficient at producing internal shocks with velocities of $5-50\,\rm km\,s^{-1}$ and Mach numbers of $\sim4-40$, which are needed to explain the $\sim 10^{-9}$…
We present SiO J=2-1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10,40] km s$^{-1}$ and an arc at velocities of [-20,10] km s$^{-1}$. The spatial anti-correlation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud-cloud collision. Some of the known compact HII regions spatially overlap with sites of strong SiO emission at velocities of [40,85] km s$^{-1}$, and are between or along the edges …
The GUAPOS project. VI: the chemical inventory of shocked gas
Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心）；Departamento de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid（马德里康普顿斯大学物理科学学院地球与天体物理学系）；INAF-Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Institut de Ciències de l’Espai (ICE, CSIC)（空间科学研究所）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；INAF-IAPS（意大利国家天体物理研究所空间和行星物理学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Department of Physics and Astronomy, University College London（伦敦大学学院物理与天文系）
We revisit an alternate explanation for the turbulent nature of molecular clouds - namely, that velocity dispersions matching classical predictions of driven turbulence can be generated by the passage of clumpy material through a shock. While previous work suggested this mechanism can reproduce the observed Larson relation between velocity dispersion and size scale ($σ\propto L^Γ$ with $Γ\approx 0.5$), the effects of self-gravity and magnetic fields were not considered. We run a series of smoothed particle magnetohydrodynamics experiments, passing clumpy gas through a shock in the presence of …
Chemical Evolution during Molecular Cloud Formation Triggered by an Interstellar Shock Wave: Dependence on Shock Parameters and Comparison with Molecular Absorption Lines
Shocks may have been prevalent in the early Universe, associated with virialization and supernova explosions, etc. Here, we study thermal evolution and fragmentation of shock-compressed clouds, by using a one-zone model with detailed thermal and chemical processes. We explore a large range of initial density (1-1e5 /cm^3), metallicity (0-1e-2 Z_sun), UV strength (0-500 times Galactic value), and cosmic microwave background temperature (10 and 30 K). Shock-compressed clouds contract isobarically via atomic and molecular line cooling, until self-gravitating clumps are formed by fragmentation. If…
Supernovae from core-collapse of massive stars drive shocks into the molecular clouds from which the stars formed. Such shocks affect future star formation from the molecular clouds, and the fast-moving, dense gas with compressed magnetic fields is associated with enhanced cosmic rays. This paper presents new theoretical modeling, using the Paris-Durham shock model, and new observations, using the Stratospheric Observatory for Infrared Astronomy (SOFIA), of the H$_2$ S(5) pure rotational line from molecular shocks in the supernova remnant IC443. We generate MHD models for non-steady-state shoc…
Evidence for Decay of Turbulence by MHD Shocks in Molecular Clouds via CO Emission
我们利用观测的亚毫米旋转转换的CO从赫歇尔周期2开放时间程序（“COPS”，PI：J.绿色），以确定以前预测的湍流耗散磁流体动力学（MHD）冲击分子云。我们发现证据的冲击预期耗散的MHD湍流的材料不与任何原恒星。两个模型的拟合程度相当：模型1的密度为10 $^{3}$ cm $^{-3}$，激波速度为3 km s $^{-1}$，磁场强度为4 $μ$ G;模型2的密度为10 $^{3.5}$ cm $^{-3}$，激波速度为$2$ km s，磁场强度为8 $μ$ G。在这一区域中，湍流衰减的时间尺度与穿越时间相当。转换的CO高达$J$的8，观察到接近恒星形成的活跃网站，但不是在外流，可以跟踪湍流耗散的冲击搅拌形成过程。虽然转换是很难在个别位置检测，我们的赫歇尔-SPIRE调查的原恒星提供了一个网格的分子云内的空间分布的光谱。我们平均了七颗原恒星附近已知流出物的所有空间位置。我们发现显着的协议与预测模型的湍流耗散在稍密（10 $^{3.5}$厘米$^{-3}$）材料具有较强的磁场（24 $μ$ G）比一般的分子云。
Instability and Evolution of Shocked Clouds Formed by Orthogonal Collisions between Magnetized Filamentary Molecular Clouds
Division of Science, National Astronomical Observatory of Japan（日本国立天文台科学部）；Center for Computational Astrophysics, National Astronomical Observatory of Japan（日本国立天文台计算天体物理学中心）；The Graduate University for Advanced Studies (SOKENDAI)（综合研究大学院大学）
Recent observations of molecular clouds show that dense filaments are the sites of present-day star formation. Thus, it is necessary to understand the filament formation process because these filaments provide the initial condition for star formation. Theoretical research suggests that shock waves in molecular clouds trigger filament formation. Since several different mechanisms have been proposed for filament formation, the formation mechanism of the observed star-forming filaments requires clarification. In the present study, we perform a series of isothermal magnetohydrodynamics simulations…
我们提出了一个公开的，开源版本的时间依赖性气体颗粒化学代码UCLCHEM。UCLCHEM通过在各种物理条件下的化学反应的大型网络传播化学物种的丰度。该模型的详细描述及其应用。作为可能用途的一个例子，UCLCHEM被用来探索原恒星坍缩对通常观察到的分子的影响，并研究C型冲击中分子的行为。我们发现一个简单的Bonnor-Ebert球的崩溃成功地再现了大部分的行为CO，CS和NH $_3$从核心观察到的\citet{Tafalla2004}，但不能预测的行为N $_2$ H $^+$。在C-shock应用中，我们发现分子可以被分类，以便它们可以成为有用的观察冲击及其物理性质的示踪剂。虽然许多分子在冲击气体中增强，但我们特别确定了两组分子。当激波传播时，少量的分子被冰的溅射所增强，然后在整个激波中保持高丰度。第二，更大的集合也被溅射增强，但随后随着气体温度的升高而被破坏。通过这些应用，UCLCHEM的普遍适用性得到了证明。
We present maps for the electron temperature in the inner kpc of three luminous Seyfert galaxies: Mrk 79, Mrk 348, and Mrk 607 obtained from Gemini GMOS-IFU observations at spatial resolutions of 110-280 pc. We study the distributions of electron temperature in active galaxies and find temperatures varying in the range from 8000 to >30000 K. Shocks due to gas outflows play an important role in the observed temperature distributions of Mrk 79 and Mrk 348, while standard photoionization models reproduce the derived temperature values for Mrk 607. In Mrk 79 and Mrk 348, we find direct evidence fo…
Formation of HI Clouds in Shock-compressed Interstellar Medium: Physical Origin of Angular Correlation Between Filamentary Structure and Magnetic Field
We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamic simulations, including non-equilibrium chemical reactions and heating/cooling processes. We consider super-Alfvénic head-on colliding flows of atomic gas possessing the two-phase structure that consists of HI clouds and surrounding warm diffuse gas. We examine how the formation of molecular clouds depends on the angle $θ$ between the upstream flow and the mean magnetic field. We find that there is a critical angle $θ_\mathrm{cr}$ above which the shock-amplified magnetic field control…
Notwithstanding manufacture of complex organic molecules from impacting cometary and icy planet surface analogues is well-established, dust grain-grain collisions driven by turbulence in interstellar or circumstellar regions may represent a parallel chemical route toward the shock synthesis of prebiotically relevant species. Here we report on a study, based on the multi-scale shock-compression technique combined with ab initio molecular dynamics approaches, where the shock-waves-driven chemistry of mutually colliding isocyanic acid (HNCO) containing icy grains has been simulated by first-princ…
Chemical complexity in star formation induced by stellar feedback: cores shock-formed by the supernova remnant W44
Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；Laboratory for the study of the Universe and eXtreme phenomena (LUX), Observatoire de Paris（巴黎天文台宇宙与极端现象实验室）；Institute of Theoretical Astrophysics, University of Oslo（奥斯陆大学理论天体物理研究所）；Department of Astronomy, University of Virginia（弗吉尼亚大学天文学系）；Institut de Radioastronomie Millimétrique（毫米波射电天文研究所）；Centro de Astrobiología (CSIC/INTA)（天体生物学中心）；INAF Osservatorio Astronomico di Arcetri（阿切特里天文台）；Rosseland Centre for Solar Physics, University of Oslo（奥斯陆大学罗斯兰太阳物理中心）；Department of Space, Earth and Environment, Chalmers University of Technology（查尔姆斯理工大学空间、地球与环境系）；Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所）；European Southern Observatory (ESO)（欧洲南方天文台）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）
Here we present our current update of CLOUDY on gas-phase chemical reactions for the formation and destruction of the SiS molecule, its energy levels, and collisional rate coefficients with H$_2$, H, and He over a wide range of temperatures. As a result, henceforth the spectral synthesis code CLOUDY predicts SiS line intensities and column densities for various astrophysical environments.
CH as a Molecular Gas Tracer and C-Shock Tracer Across a Molecular Cloud Boundary in Taurus
我们提出了新的观测所有三个基态跃迁的次甲基（CH）自由基和所有四个基态跃迁的羟基（OH）自由基对一个尖锐的边界区域的金牛座分子云。这些数据与现有的CO和灰尘图像进行了分析。推导出的CH丰度与以前的半透明云（$0.8\le A_{v} \le 2.1$等）的观测结果一致。在此消光范围内，$X({\rm CH})$ -因子在$(1.0\pm0.06)\times 10^{22}$ $\rm {cm^{-2}~K^{-1}~km^{-1}~s}$处几乎为常数，其色散小于更广泛使用的分子示踪剂CO和OH的色散。结果表明，CH是一个更好的总柱密度在这样的中间消光范围比CO或OH的示踪剂。与以前的观测结果相比，CH在1等灭绝以下是过剩的。这种CH的过量与C型休克的存在是一致的。CH有两个运动学分量，当从云外向云内移动时，其中一个从5.3 km s $^{-1}$移动到6 km s，而另一个保持在6.8 km s $^{-1}$。这些速度行为与以前的OH观测结果完全吻合。这两个运动分量的移动表明在边界区域的碰撞流或气体流动，这可能是C-激波的原因。
Using integral field data we extract the optical spectra of shocked interstellar clouds in Kepler's supernova remnant located in the inner regions of our Galaxy, as well as in the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), NGC6822 and IC 1613. Using self-consistent shock modelling, we make a new determination of the chemical composition of the interstellar medium (ISM) in N, O, Ne, S, Cl and Ar in these galaxies and obtain accurate estimates of the fraction of refractory grains destroyed in the shock. By comparing our derived abundances with those obtained in recent works …
Sulphur within the extreme environment of the central molecular zone of NGC 253: a chemical modelling approach
Leiden University（莱顿大学）；University of Bonn（波恩大学）；University College London（伦敦大学学院）；National Radio Astronomy Observatory（美国国家射电天文台）；University of Virginia（弗吉尼亚大学）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）
We build detailed composite models of photoionization and shock ionization based on the SUMA code to reproduce emission lines emitted from the Narrow Line Regions (NLR) of Seyfert 2 nuclei. The aim of this work is to investigate diagram AGN positions according to shock parameters, shock effects on the gas temperature and ionization structures and derive a semi-empirical abundance calibration based on emission-line ratios little sensitive to the shock presence. The models were used to reproduce optical (3000 < A < 7000) emission line intensities of 244 local (z < 0.4) Seyfert 2s, whose observat…
We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamical simulations,including non-equilibrium chemical reactions, heating/cooling processes, and self-gravity by changing the collision speed $V_0$ and the angle $θ$ between the magnetic field and colliding flow. We found that the efficiency of the dense gas formation depends on $θ$. For small $θ$, anisotropic super-Alfvénic turbulence delays the formation of gravitationally unstable clumps. An increase in $θ$ develops shock-amplified magnetic fields along which the gas is accumulated, mak…
