Hyperbolic self-gravity solver for large scale hydrodynamical simulations

ABSTRACT We use hydrodynamical simulations to study the Milky Way’s central molecular zone (CMZ). The simulations include a non-equilibrium chemical network, the gas self-gravity, star formation, and supernova feedback. We resolve the structure of the interstellar medium at sub-parsec resolution while also capturing the interaction between the CMZ and the bar-driven large-scale flow out to $R\sim 5\, {\rm kpc}$. Our main findings are as follows: (1) The distinction between inner (R ≲ 120 pc) and outer (120 ≲ R ≲ 450 pc) CMZ that is sometimes proposed in the literature is unnecessary. Instead, the CMZ is best described as single structure, namely a star-forming ring with outer radius R ≃ 200 pc which includes the 1.3° complex and which is directly interacting with the dust lanes that mediate the bar-driven inflow. (2) This accretion can induce a significant tilt of the CMZ out of the plane. A tilted CMZ might provide an alternative explanation to the ∞-shaped structure identified in Herschel data by Molinari et al. (3) The bar in our simulation efficiently drives an inflow from the Galactic disc (R ≃ 3 kpc) down to the CMZ (R ≃ 200 pc) of the order of $1\rm \, M_\odot \, yr^{-1}$, consistent with observational determinations. (4) Supernova feedback can drive an inflow from the CMZ inwards towards the circumnuclear disc of the order of ${\sim}0.03\, \rm M_\odot \, yr^{-1}$. (5) We give a new interpretation for the 3D placement of the 20 and 50 km s−1 clouds, according to which they are close (R ≲ 30 pc) to the Galactic Centre, but are also connected to the larger scale streams at R ≳ 100 pc.

Download Full-text

The anisotropy of the power spectrum in periodic cosmological simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab874 ◽

2021 ◽

Vol 503 (4) ◽

pp. 5638-5645

Author(s):

Gábor Rácz ◽

István Szapudi ◽

István Csabai ◽

László Dobos

Keyword(s):

Dark Matter ◽

Power Spectrum ◽

Large Scale ◽

Cold Dark Matter ◽

Initial Conditions ◽

Power Spectra ◽

Cosmological Simulations ◽

Spherical Collapse ◽

Lower Amplitude ◽

Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

Download Full-text

Filament Formation in Molecular Clouds as a Scale-Free Process

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006463 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 709-710

Author(s):

Enrique Vázquez-Semadeni ◽

Gilberto Gómez

Keyword(s):

Hierarchical Structure ◽

Molecular Clouds ◽

Large Scale ◽

Filament Formation ◽

Molecular Line ◽

Scale Free ◽

The Core ◽

Free Process ◽

Self Gravity

AbstractWe discuss the formation of filaments in molecular clouds (MCs) as the result of large-scale collapse in the clouds. We first give arguments suggesting that self-gravity dominates the nonthermal motions, and then briefly describe the resulting structure, similar to that found in molecular-line and dust observations of the filaments in the clouds. The filaments exhibit a hierarchical structure in both density and velocity, suggesting a scale-free nature, similar to that of the cosmic web, resulting from the domination of self-gravity from the MC down to the core scale.

Download Full-text

Thawing the frozen-in approximation: implications for self-gravity in deeply plunging tidal disruption events

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slz048 ◽

2019 ◽

Vol 485 (1) ◽

pp. L146-L150 ◽

Cited By ~ 18

Author(s):

Elad Steinberg ◽

Eric R Coughlin ◽

Nicholas C Stone ◽

Brian D Metzger

Keyword(s):

Free Fall ◽

Tidal Disruption ◽

Massive Black Hole ◽

High Penetration ◽

Order Of Magnitude ◽

Sphere Radius ◽

Hydrodynamical Simulations ◽

Self Gravity ◽

Hydrostatic Balance ◽

Mesh Technique

ABSTRACT The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the ‘frozen-in’ approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β ≡ rt/rp = 5−7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

Download Full-text

Finding and characterising WHIM structures using the luminosity density method

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010188 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 368-371

Author(s):

Jukka Nevalainen ◽

L. J. Liivamägi ◽

E. Tempel ◽

E. Branchini ◽

M. Roncarelli ◽

...

Keyword(s):

Large Scale ◽

Real Data ◽

Sloan Digital Sky Survey ◽

Physical Parameters ◽

X Ray ◽

Galaxy Surveys ◽

Sky Survey ◽

The Galaxy ◽

Hydrodynamical Simulations ◽

X Ray Absorption

AbstractWe have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) mapping its luminosity into a galaxy luminosity density field, (c) using numerical simulations to relate the luminosity density to the density of the WHIM, (d) applying this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density NH in Sculptor agree with those obtained via the X-ray analysis. Due to the additional NH estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem.

Download Full-text

Neutral Hydrogen in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s007418090011736x ◽

1999 ◽

Vol 190 ◽

pp. 37-44

Author(s):

L. Staveley-Smith ◽

S. Kim ◽

S. Stanimirović

Keyword(s):

Atomic Hydrogen ◽

Large Scale ◽

Milky Way ◽

Velocity Dispersion ◽

Neutral Hydrogen ◽

Distribution Functions ◽

Magellanic Clouds ◽

Self Gravity ◽

Rotational Shear ◽

Compact Array

We review observations of neutral atomic hydrogen (HI) in the Magellanic Clouds (MCs). Being the nearest gas-rich neighbours of the Milky Way the MCs give us an excellent opportunity to study in detail the structure and evolution of the interstellar medium (ISM) and the effect of interactions between galaxies. HI in emission provides a probe of the structure and velocity field of the Clouds, allowing the study of their velocity dispersion, 3-D structure, and large-scale total-mass distribution. Recent data from Australia Telescope Compact Array surveys reveal a morphology (for both Clouds) which is heavily dominated by the effects of local star-formation, rotational shear, fragmentation, self-gravity and turbulence. The new data, which has a spatial resolution down to 10 pc, also allows the study of the distribution functions in velocity and mass for HI clouds. We discuss the morphology, dynamics and giant shell population of the LMC and SMC.

Download Full-text

Dynamics of Type-II Supernovae

International Astronomical Union Colloquium ◽

10.1017/s0252921100007971 ◽

1996 ◽

Vol 145 ◽

pp. 109-117 ◽

Cited By ~ 1

Author(s):

H.-Th. Janka ◽

E. M. Müller

Keyword(s):

Large Scale ◽

Energy Deposition ◽

Supernova Explosion ◽

Threshold Value ◽

Neutrino Energy ◽

Two Dimensions ◽

Iron Core ◽

Type Ii ◽

Convective Processes ◽

Hydrodynamical Simulations

Hydrodynamical simulations of type-II supernovae in one and two dimensions are performed for the revival phase of the delayed shock by neutrino energy deposition. Starting with a post-collapse model of the 1.31 Mʘ iron core of a 15 Mʘ star immediately after the stagnation of the prompt shock about 10 ms after core bounce, the models are followed for several hundred milliseconds with varied neutrino fluxes from the neutrino sphere. The variation of the neutrino luminosities is motivated by the considerable increase of the neutrino emission due to convective processes inside and close to the neutrino sphere (see Janka 1993), which are driven by negative gradients of entropy and electron concentration left behind by the prompt shock (Burrows & Fryxell 1992, Janka & Müller 1992). The size of this luminosity increase remains to be quantitatively analyzed yet and may require multi-dimensional neutrino transport. However, in the presented simulations the region below the neutrino sphere is cut out and replaced by an inner boundary condition, so that the convective zone is only partially included and the neutrino flows are treated as a freely changeable energy source.For small neutrino luminosities the energy transfer to the matter is insufficient to revive the stalled shock. However, there is a sharp transition to successful explosions, when the neutrino luminosities lie above some ‘threshold value’. Once the shock is driven out and the density and temperature of the matter between neutrino sphere and shock start to decrease during the expansion, suitable conditions for further neutrino energy deposition are maintained, and an explosion results. With the neutrino energy deposition the entropy per nucleon in the region between neutrino sphere and shock grows, and convective overturn will set in. Multi-dimensional simulations show that due to the large pressure scale height a large-scale pattern of up-flows and down-flows with velocities close to the local speed of sound develops. Consequently, cold, postshock material is advected down into the neutrino heating layer close to the neutrino sphere and hot material is transported outwards, thus reducing energy losses by re-emission of neutrinos and increasing the pressure behind the shock. Therefore these convective processes are found to be a very important aid to the delayed supernova explosion. In fact, two-dimensional models explode even in cases where spherically symmetrical computations fail.

Download Full-text

Simulations of the star-forming molecular gas in an interacting M51-like galaxy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3600 ◽

2020 ◽

Vol 492 (2) ◽

pp. 2973-2995 ◽

Cited By ~ 11

Author(s):

Robin G Tress ◽

Rowan J Smith ◽

Mattia C Sormani ◽

Simon C O Glover ◽

Ralf S Klessen ◽

...

Keyword(s):

Star Formation ◽

Large Scale ◽

Formation Rate ◽

Three Dimensional ◽

Molecular Gas ◽

Secondary Importance ◽

Star Forming ◽

The Galaxy ◽

Cold Star ◽

Self Gravity

ABSTRACT We present here the first of a series of papers aimed at better understanding the evolution and properties of giant molecular clouds (GMCs) in a galactic context. We perform high-resolution, three-dimensional arepo simulations of an interacting galaxy inspired by the well-observed M51 galaxy. Our fiducial simulations include a non-equilibrium, time-dependent, chemical network that follows the evolution of atomic and molecular hydrogen as well as carbon and oxygen self-consistently. Our calculations also treat gas self-gravity and subsequent star formation (described by sink particles), and coupled supernova feedback. In the densest parts of the simulated interstellar medium (ISM), we reach sub-parsec resolution, granting us the ability to resolve individual GMCs and their formation and destruction self-consistently throughout the galaxy. In this initial work, we focus on the general properties of the ISM with a particular focus on the cold star-forming gas. We discuss the role of the interaction with the companion galaxy in generating cold molecular gas and controlling stellar birth. We find that while the interaction drives large-scale gas flows and induces spiral arms in the galaxy, it is of secondary importance in determining gas fractions in the different ISM phases and the overall star formation rate. The behaviour of the gas on small GMC scales instead is mostly controlled by the self-regulating property of the ISM driven by coupled feedback.

Download Full-text

Molecular cloud formation by compression of magnetized turbulent gas subjected to radiative cooling

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa468 ◽

2020 ◽

Vol 493 (3) ◽

pp. 3098-3113 ◽

Cited By ~ 5

Author(s):

Ankush Mandal ◽

Christoph Federrath ◽

Bastian Körtgen

Keyword(s):

Molecular Cloud ◽

Large Scale ◽

Turnover Rate ◽

Radiative Heating ◽

Cloud Formation ◽

Neutral Medium ◽

Contraction Rate ◽

Mhd Turbulence ◽

Cloud Properties ◽

Hydrodynamical Simulations

ABSTRACT Complex turbulent motions of magnetized gas are ubiquitous in the interstellar medium (ISM). The source of this turbulence, however, is still poorly understood. Previous work suggests that compression caused by supernova shockwaves, gravity, or cloud collisions, may drive the turbulence to some extent. In this work, we present three-dimensional (3D) magnetohydrodynamic (MHD) simulations of contraction in turbulent, magnetized clouds from the warm neutral medium of the ISM to the formation of cold dense molecular clouds, including radiative heating and cooling. We study different contraction rates and find that observed molecular cloud properties, such as the temperature, density, Mach number, and magnetic field strength, and their respective scaling relations, are best reproduced when the contraction rate equals the turbulent turnover rate. In contrast, if the contraction rate is significantly larger (smaller) than the turnover rate, the compression drives too much (too little) turbulence, producing unrealistic cloud properties. We find that the density probability distribution function evolves from a double lognormal representing the two-phase ISM, to a skewed, single lognormal in the dense, cold phase. For purely hydrodynamical simulations, we find that the effective driving parameter of contracting cloud turbulence is natural to mildly compressive (b ∼ 0.4–0.5), while for MHD turbulence, we find b ∼ 0.3–0.4, i.e. solenoidal to naturally mixed. Overall, the physical properties of the simulated clouds that contract at a rate equal to the turbulent turnover rate, indicate that large-scale contraction may explain the origin and evolution of turbulence in the ISM.

Download Full-text

Hydrodynamical simulations of the barred spiral galaxy NGC 1097

Proceedings of the International Astronomical Union ◽

10.1017/s174392131401148x ◽

2012 ◽

Vol 10 (H16) ◽

pp. 376-376

Author(s):

Lien-Hsuan Lin ◽

Hsiang-Hsu Wang ◽

Pei-Ying Hsieh ◽

Ronald E. Taam ◽

Chao-Chin Yang ◽

...

Keyword(s):

Spiral Galaxy ◽

Gas Flow ◽

Elliptical Galaxy ◽

The Self ◽

Two Dimensional ◽

Nuclear Ring ◽

Barred Spiral Galaxy ◽

Circumnuclear Disk ◽

Hydrodynamical Simulations ◽

Self Gravity

AbstractNGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable which is consistent with the observation in Hsieh et al. (2011). Our simulations also show that gas can flow into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.

Download Full-text