| 1. |
- Agertz, Oscar, et al.
(författare)
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Characterizing gravitational instability in turbulent multicomponent galactic discs
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 449:2, s. 2156-2166
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Tidskriftsartikel (refereegranskat)abstract
- Gravitational instabilities play an important role in galaxy evolution and in shaping the interstellar medium (ISM). The ISM is observed to be highly turbulent, meaning that observables like the gas surface density and velocity dispersion depend on the size of the region over which they are measured. In this work, we investigate, using simulations of Milky Way-like disc galaxies with a resolution of ∼ 9 pc, the nature of turbulence in the ISM and how this affects the gravitational stability of galaxies. By accounting for the measured average turbulent scalings of the density and velocity fields in the stability analysis, we can more robustly characterize the average level of stability of the galaxies as a function of scale, and in a straightforward manner identify scales prone to fragmentation. Furthermore, we find that the stability of a disc with feedback-driven turbulence can be well described by a ‘Toomre-like' Q stability criterion on all scales, whereas the classical Q can formally lose its meaning on small scales if violent disc instabilities occur in models lacking pressure support from stellar feedback.
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| 2. |
- Agertz, O., et al.
(författare)
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Large-scale galactic turbulence: can self-gravity drive the observed HI velocity dispersions?
- 2009
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 392:1, s. 294-308
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Tidskriftsartikel (refereegranskat)abstract
- Observations of turbulent velocity dispersions in the HI component of galactic discs show a characteristic floor in galaxies with low star formation rates and within individual galaxies the dispersion profiles decline with radius. We carry out several high-resolution adaptive mesh simulations of gaseous discs embedded within dark matter haloes to explore the roles of cooling, star formation, feedback, shearing motions and baryon fraction in driving turbulent motions. In all simulations the disc slowly cools until gravitational and thermal instabilities give rise to a multiphase medium in which a large population of dense self-gravitating cold clouds are embedded within a warm gaseous phase that forms through shock heating. The diffuse gas is highly turbulent and is an outcome of large-scale driving of global non-axisymmetric modes as well as cloud-cloud tidal interactions and merging. At low star formation rates these processes alone can explain the observed HI velocity dispersion profiles and the characteristic value of similar to 10 km s(-1) observed within a wide range of disc galaxies. Supernovae feedback creates a significant hot gaseous phase and is an important driver of turbulence in galaxies with a star formation rate per unit area greater than or similar to 10(-3) M(circle dot) yr(-1) kpc(-2).
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| 3. |
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| 4. |
- Agertz, Oscar, et al.
(författare)
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Virtual Universes
- 2011
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Ingår i: Tofsen. ; :4, s. 38-39
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Antonuccio-Delogu, V., et al.
(författare)
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Properties of galaxy haloes in clusters and voids
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 332:1, s. 7-20
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Tidskriftsartikel (refereegranskat)abstract
- We use the results of a high-resolution N -body simulation to investigate the role of the environment on the formation and evolution of galaxy-sized haloes. Starting from a set of constrained initial conditions, we have produced a final configuration hosting a double cluster in one octant and a large void extending over two octants of the simulation box. In this paper we concentrate on gravitationally bound galaxy-sized haloes extracted from these two regions and from a third region hosting a single, relaxed cluster without substructure. Exploiting the high mass resolution of our simulation (m body =2.1×109 h -1 Msolar ), we construct halo samples probing more than two decades in mass, starting from a rather small mass threshold: 5×1010 h -1 Msolar =34.2r 0 , where r 0 is the core radius of the TIS solution). We do, however, find a dependence of this relationship on the environment, like for the P (lambda ) statistics. These facts hint at a possible role of tidal fields in determining the statistical properties of haloes.
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| 6. |
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| 7. |
- Bertin, G., et al.
(författare)
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Global spiral modes in stellar disks containing gas
- 1988
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 195, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- The authors present a linear study of the role of gas on global spiral modes in stellar disks using a simple two-fluid model. The local destabilizing role of a cold component has been known for many years and calculated by various authors. The authors confirm the effectiveness of a small amount of gas in fueling spiral instabilities with a response which is primarily at short wavelengths by constructing a synthetic diagram which summarizes the local stability analysis. Then they proceed to consider global spiral modes in two-component systems with applications to regimes of astrophysical interest that are expected to be associated with normal spiral structure. Moderate growth spiral modes are found that are very close in structure to those of one-component systems, but for substantially higher values of the stability parameter Q. A simple model of self-regulation is also presented.
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| 8. |
- Ejdetjärn, Timmy, et al.
(författare)
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From giant clumps to clouds - III. The connection between star formation and turbulence in the ISM
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 514:1, s. 480-496
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Tidskriftsartikel (refereegranskat)abstract
- Supersonic gas turbulence is a ubiquitous property of the interstellar medium. The level of turbulence, quantified by the gas velocity dispersion (sigma(g)), is observed to increase with the star formation rate (SFR) of a galaxy, but it is yet not established whether this trend is driven by stellar feedback or gravitational instabilities. In this work, we carry out hydrodynamical simulations of entire disc galaxies, with different gas fractions, to understand the origins of the SFR-sigma(g) relation. We show that disc galaxies reach the same levels of turbulence regardless of the presence of stellar feedback processes, and argue that this is an outcome of the way disc galaxies regulate their gravitational stability. The simulations match the SFR-sigma(g) relation up to SFRs of the order of tens of M-circle dot yr(-1) and sigma(g) similar to 50 km s(-1) in neutral hydrogen and molecular gas, but fail to reach the very large values (> 100 km s(-1)) reported in the literature for rapidly star-forming galaxies. We demonstrate that such high values of sigma(g) can be explained by ( 1) insufficient beam smearing corrections in observations and (2) stellar feedback being coupled to the ionized gas phase traced by recombination lines. Given that the observed SFR-sigma(g) relation is composed of highly heterogeneous data, with sigma(g) at high SFRs almost exclusively being derived from H alpha observations of high-redshift galaxies with complex morphologies, we caution against analytical models that attempt to explain the SFR-sigma(g) relation without accounting for these effects.
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| 9. |
- Fathi, Kambiz, et al.
(författare)
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LOCAL INSTABILITY SIGNATURES IN ALMA OBSERVATIONS OF DENSE GAS IN NGC 7469
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213 .- 1538-4357 .- 0004-637X. ; 806:2
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Tidskriftsartikel (refereegranskat)abstract
- We present an unprecedented measurement of the disk stability and local instability scales in the luminous infrared Seyfert 1 host, NGC 7469, based on ALMA observations of dense gas tracers and with a synthesized beam of 165 x 132 pc. While we confirm that non-circular motions are not significant in redistributing the dense interstellar gas in this galaxy, we find compelling evidence that the dense gas is a suitable tracer for studying the origin of its intensely high-mass star-forming ringlike structure. Our derived disk stability parameter Q accounts for a thick disk structure, and its value falls below unity at the radii in which intense star formation is found. Furthermore, we derive the characteristic instability scale lambda(c) and find a striking agreement between our measured scale of similar to 180 pc and the typical sizes of individual complexes of young and massive star clusters seen in high-resolution images.
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| 10. |
- Grisdale, Kearn, et al.
(författare)
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On the observed diversity of star formation efficiencies in Giant Molecular Clouds
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 486:4, s. 5482-5491
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Tidskriftsartikel (refereegranskat)abstract
- Observations find a median star formation efficiency per free-fall time in Milky Way Giant Molecular Clouds (GMCs) of the order of eff ~ 1 per cent with dispersions of ~0.5dex. The origin of this scatter in eff is still debated and difficult to reproduce with analytical models.We track the formation, evolution and destruction of GMCs in a hydrodynamical simulation of a Milky Way-like galaxy and by deriving cloud properties in an observationally motivated way, we measure the distribution of star formation efficiencies which are in excellent agreement with observations. We find no significant link between eff and any measured global property of GMCs (e.g. gas mass, velocity dispersion). Instead, a wide range of efficiencies exist in the entire parameter space. From the cloud evolutionary tracks, we find that each cloud follows a unique evolutionary path which gives rise to a wide diversity in all properties.We argue that it is this diversity in cloud properties, above everything else, that results in the dispersion of eff .
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