scholarly journals Simulations of the Milky Way’s central molecular zone – I. Gas dynamics

2020 ◽  
Vol 499 (3) ◽  
pp. 4455-4478
Author(s):  
Robin G Tress ◽  
Mattia C Sormani ◽  
Simon C O Glover ◽  
Ralf S Klessen ◽  
Cara D Battersby ◽  
...  
Keyword(s):  
Large Scale ◽  
Outer Radius ◽  
Galactic Centre ◽  
Star Forming ◽  
Single Structure ◽  
New Interpretation ◽  
Hydrodynamical Simulations ◽  
Large Scale Flow ◽  
Self Gravity ◽  
Supernova Feedback

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.

scholarly journals Properties of the circumgalactic medium in simulations compared to observations

2018 ◽  
Vol 609 ◽  
pp. A66 ◽  
Author(s):  
R. E. G. Machado ◽  
P. B. Tissera ◽  
G. B. Lima Neto ◽  
L. Sodré
Keyword(s):  
Gas Phase ◽  
Chemical Elements ◽  
Star Forming ◽  
Physical Conditions ◽  
Cosmological Context ◽  
Circumgalactic Medium ◽  
Hydrodynamical Simulations ◽  
Stellar Masses ◽  
Lower Limits ◽  
Supernova Feedback

Context. Galaxies are surrounded by extended gaseous halos that store significant fractions of chemical elements. These are syntethized by the stellar populations and later ejected into the circumgalactic medium (CGM) by different mechanism, of which supernova feedback is considered one of the most relevant. Aims. We aim to explore the properties of this metal reservoir surrounding star-forming galaxies in a cosmological context aiming to investigate the chemical loop between galaxies and their CGM, and the ability of the subgrid models to reproduce observational results. Methods. Using cosmological hydrodynamical simulations, we have analysed the gas-phase chemical contents of galaxies with stellar masses in the range 109−1011 M⊙. We estimated the fractions of metals stored in the different CGM phases, and the predicted O vi and Si iii column densities within the virial radius. Results. We find roughly 107 M⊙ of oxygen in the CGM of simulated galaxies having M⋆ ~ 1010 M⊙, in fair agreement with the lower limits imposed by observations. The Moxy is found to correlate with M⋆, at odds with current observational trends but in agreement with other numerical results. The estimated profiles of O vi column density reveal a substantial shortage of that ion, whereas Si iii, which probes the cool phase, is overpredicted. Nevertheless, the radial dependences of both ions follow the respective observed profiles. The analysis of the relative contributions of both ions from the hot, warm and cool phases suggests that the warm gas (105 K < T < 106 K) should be more abundant in order to bridge the mismatch with the observations, or alternatively, that more metals should be stored in this gas-phase. These discrepancies provide important information to improve the subgrid physics models. Our findings show clearly the importance of tracking more than one chemical element and the difficulty of simultaneously satisfying the observables that trace the circumgalactic gas at different physical conditions. Additionally, we find that the X-ray coronae around the simulated galaxies have luminosities and temperatures in decent agreement with the available observational estimates.

scholarly journals Global simulations of galactic discs: violent feedback from clustered supernovae during bursts of star formation

2019 ◽  
Vol 492 (1) ◽  
pp. 79-95 ◽  
Author(s):  
Davide Martizzi
Keyword(s):  
Adaptive Mesh Refinement ◽  
Gravitational Instability ◽  
Adaptive Mesh ◽  
Dark Matter Halo ◽  
Time Variability ◽  
Mass Loading ◽  
Star Forming ◽  
Galactic Winds ◽  
Self Gravity ◽  
Supernova Feedback

ABSTRACT A suite of idealized, global, gravitationally unstable, star-forming galactic disc simulations with 2 pc spatial resolution, performed with the adaptive mesh refinement code ramses, is used in this paper to predict the emergent effects of supernova feedback. The simulations include a simplified prescription for the formation of single stellar populations of mass $\sim 100 \, {\rm M}_{\odot }$, radiative cooling, photoelectric heating, an external gravitational potential for a dark matter halo and an old stellar disc, self-gravity, and a novel implementation of supernova feedback. The results of these simulations show that gravitationally unstable discs can generate violent supersonic winds with mass-loading factors η ≳ 10, followed by a galactic fountain phase. These violent winds are generated by highly clustered supernovae exploding in dense environments created by gravitational instability, and they are not produced in simulation without self-gravity. The violent winds significantly perturb the vertical structure of the disc, which is later re-established during the galactic fountain phase. Gas resettles into a quasi-steady, highly turbulent disc with volume-weighted velocity dispersion $\sigma \gt 50 \, {\rm km\, s}^{-1}$. The new configuration drives weaker galactic winds with a mass-loading factor η ≤ 0.1. The whole cycle takes place in ≤10 dynamical times. Such high time variability needs to be taken into account when interpreting observations of galactic winds from starburst and post-starburst galaxies.

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

2020 ◽  
Vol 492 (2) ◽  
pp. 2973-2995 ◽  
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.

scholarly journals Hyperbolic self-gravity solver for large scale hydrodynamical simulations

2016 ◽  
Vol 93 (8) ◽  
Author(s):  
Ryosuke Hirai ◽  
Hiroki Nagakura ◽  
Hirotada Okawa ◽  
Kotaro Fujisawa
Keyword(s):  
Large Scale ◽  
Hydrodynamical Simulations ◽  
Self Gravity

scholarly journals The SEDIGISM survey: First Data Release and overview of the Galactic structure

2020 ◽  
Vol 500 (3) ◽  
pp. 3064-3082 ◽  
Author(s):  
F Schuller ◽  
J S Urquhart ◽  
T Csengeri ◽  
D Colombo ◽  
A Duarte-Cabral ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Large Scale ◽  
Galactic Plane ◽  
Structural Features ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Spiral Arms ◽  
Star Forming ◽  
Wide Range ◽  
Data Release

ABSTRACT The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg2 of the Galactic plane between ℓ = −60° and +31° in several molecular transitions, including 13CO (2 – 1) and C18O (2 – 1), thus probing the moderately dense (∼103 cm−3) component of the interstellar medium. With an angular resolution of 30 arcsec and a typical 1σ sensitivity of 0.8–1.0 K at 0.25 km s−1 velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large-scale distribution of cold molecular gas in the inner Galaxy. In this paper, we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this First Data Release (DR1). We present integrated maps and position–velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large-scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic Centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic Centre and well-known star-forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.

scholarly journals How runaway stars boost galactic outflows

2020 ◽  
Vol 494 (3) ◽  
pp. 3328-3341 ◽  
Author(s):  
Eric P Andersson ◽  
Oscar Agertz ◽  
Florent Renaud
Keyword(s):  
Interstellar Medium ◽  
Large Scale ◽  
Ob Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Order Of Magnitude ◽  
Hydrodynamical Simulations ◽  
Scale Properties ◽  
Energy And Momentum ◽  
Runaway Stars

ABSTRACT Roughly 10 per cent of OB stars are kicked out of their natal clusters before ending their life as supernovae. These so-called runaway stars can travel hundreds of parsecs into the low-density interstellar medium, where momentum and energy from stellar feedback is efficiently deposited. In this work, we explore how this mechanism affects large-scale properties of the galaxy, such as outflows. To do so we use a new model that treats OB stars and their associated feedback processes on a star-by-star basis. With this model, we compare two hydrodynamical simulations of Milky Way-like galaxies, one where we include runaways, and one where we ignore them. Including runaway stars leads to twice as many supernovae explosions in regions with gas densities ranging from $10^{-5}\, \mathrm{\,cm^{-3}}$ to $10^{-3}\, \mathrm{\,cm^{-3}}$. This results in more efficient heating of the inter-arm regions, and drives strong galactic winds with mass loading factors boosted by up to one order of magnitude. These outflows produce a more massive and extended multiphase circumgalactic medium, as well as a population of dense clouds in the halo. Conversely, since less energy and momentum is released in the dense star-forming regions, the cold phase of the interstellar medium is less disturbed by feedback effects.

scholarly journals The life cycle of the Central Molecular Zone – I. Inflow, star formation, and winds

2019 ◽  
Vol 490 (3) ◽  
pp. 4401-4418 ◽  
Author(s):  
Lucia Armillotta ◽  
Mark R Krumholz ◽  
Enrico M Di Teodoro ◽  
N M McClure-Griffiths
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Galactic Centre ◽  
Two Phase ◽  
Star Forming ◽  
Stellar Feedback ◽  
Order Of Magnitude ◽  
Hydrodynamical Simulations

ABSTRACT We present a study of the gas cycle and star formation history in the central 500 pc of the Milky Way, known as Central Molecular Zone (CMZ). Through hydrodynamical simulations of the inner 4.5 kpc of our Galaxy, we follow the gas cycle in a completely self-consistent way, starting from gas radial inflow due to the Galactic bar, the channelling of this gas into a dense, star-forming ring/stream at ≈200–300 pc from the Galactic centre, and the launching of galactic outflows powered by stellar feedback. We find that star formation activity in the CMZ goes through oscillatory burst/quench cycles, with a period of tens to hundreds of Myr, characterized by roughly constant gas mass but order-of-magnitude level variations in the star formation rate. Comparison with the observed present-day star formation rate of the CMZ suggests that we are currently near a minimum of this cycle. Stellar feedback drives a mainly two-phase wind off the Galactic disc. The warm phase dominates the mass flux, and carries $100\!-\!200{{\ \rm per\ cent}}$ of the gas mass converted into stars. However, most of this gas goes into a fountain and falls back on to the disc rather than escaping the Galaxy. The hot phase carries most of the energy, with a time-averaged energy outflow rate of $10\!-\!20{{\ \rm per\ cent}}$ of the supernova energy budget.

scholarly journals Simulations of the Milky Way’s Central Molecular Zone – II. Star formation

2020 ◽  
Vol 497 (4) ◽  
pp. 5024-5040 ◽  
Author(s):  
Mattia C Sormani ◽  
Robin G Tress ◽  
Simon C O Glover ◽  
Ralf S Klessen ◽  
Cara D Battersby ◽  
...  
Keyword(s):  
Star Formation ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Formation Rate ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
Zone Ii ◽  
Sgr A ◽  
Large Scale Flow ◽  
Induced Changes

ABSTRACT The Milky Way’s Central Molecular Zone (CMZ) has emerged in recent years as a unique laboratory for the study of star formation. Here we use the simulations presented in Tress et al. to investigate star formation in the CMZ. These simulations resolve the structure of the interstellar medium at sub-parsec resolution while also including the large-scale flow in which the CMZ is embedded. Our main findings are as follows. (1) While most of the star formation happens in the CMZ ring at $R\gtrsim 100 \, {\rm pc}$, a significant amount also occurs closer to Sgr A* at $R \lesssim 10\, {\rm pc}$. (2) Most of the star formation in the CMZ happens downstream of the apocentres, consistent with the ‘pearls-on-a-string’ scenario, and in contrast to the notion that an absolute evolutionary timeline of star formation is triggered by pericentre passage. (3) Within the time-scale of our simulations (∼100 Myr), the depletion time of the CMZ is constant within a factor of ∼2. This suggests that variations in the star formation rate are primarily driven by variations in the mass of the CMZ, caused, for example, by active galactic nuclei (AGN) feedback or externally induced changes in the bar-driven inflow rate, and not by variations in the depletion time. (4) We study the trajectories of newly born stars in our simulations. We find several examples that have age and 3D velocity compatible with those of the Arches and Quintuplet clusters. Our simulations suggest that these prominent clusters originated near the collision sites where the bar-driven inflow accretes on to the CMZ, at symmetrical locations with respect to the Galactic Centre, and that they have already decoupled from the gas in which they were born.

scholarly journals Birthing star forming clouds in the grand design

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Yusuke Fujimoto ◽  
Elizabeth J. Tasker ◽  
Greg L. Bryan ◽  
Asao Habe
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Galactic Centre ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Stellar Feedback ◽  
Star Formation Activity ◽  
Grand Design ◽  
Centre Region ◽  
Hydrodynamical Simulations

AbstractWe performed high resolution 3D hydrodynamical simulations of the barred galaxy M83 and investigated formation and evolution of the giant molecular clouds (GMCs) and star formation activity. We compared two simulations with and without stellar feedback. We found that the feedback disperses the cloud gas and causes clouds to inflow toward the galactic centre region due to hydrodynamical drag. The effect raises the star formation rate (SFR) and star formation efficiency (SFE) in the central bar region.

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