Lessons from the Local Group

Freeman, K. C.; Elmegreen, Bruce; Block, David L.; Woolway, Matthew

doi:10.1007/978-3-319-10614-4

2015

DOI: 10.1007/978-3-319-10614-4

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Lessons from the Local Group

K. C. Freeman¹,

Bruce Elmegreen²,

David L. Block³

et al.

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Cited by 4 publications

References 754 publications

(1,063 reference statements)

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Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

Suzuki

Fukui

Torii

et al. 2015

Mon. Not. R. Astron. Soc.

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By performing a global magneto-hydrodynamical simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic center region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches > ∼ 0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. In addition, the magnetic pressuregradient force also drives radial flows in a similar manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram-shape of the central molecular zone. This is a natural extension into the central few 100 pc of the magnetic activity, which is observed as molecular loops at radii from a few 100 pc to 1 kpc. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time-dependent, which we discuss from a viewpoint of the outflow from the bulge.

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Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

Suzuki

Fukui

Torii

et al. 2015

Mon. Not. R. Astron. Soc.

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show abstract

Hubble–Lemaître fragmentation and the path to equilibrium of merger-driven cluster formation

Dorval

Boily

Moraux

et al. 2016

Mon. Not. R. Astron. Soc.

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This paper discusses a new method to generate self-coherent initial conditions for young substructured stellar cluster. The expansion of a uniform system allows stellar sub-structures (clumps) to grow from fragmentation modes by adiabatic cooling. We treat the system mass elements as stars, chosen according to a Salpeter mass function, and the time-evolution is performed with a collisional N-body integrator. This procedure allows to create a fully-coherent relation between the clumps' spatial distribution and the underlying velocity field. The cooling is driven by the gravitational field, as in a cosmological Hubble-Lemaître flow. The fragmented configuration has a 'fractal'like geometry but with a self-grown velocity field and mass profile. We compare the characteristics of the stellar population in clumps with that obtained from hydrodynamical simulations and find a remarkable correspondence between the two in terms of the stellar content and the degree of spatial mass-segregation. In the fragmented configuration, the IMF power index is ≈ 0.3 lower in clumps in comparison to the field stellar population, in agreement with observations in the Milky Way. We follow in time the dynamical evolution of fully fragmented and sub-virial configurations, and find a soft collapse, leading rapidly to equilibrium (timescale of 1 Myr for a ∼ 10 4 M ⊙ system). The low-concentration equilibrium implies that the dynamical evolution including massive stars is less likely to induce direct collisions and the formation of exotic objects. Low-mass stars already ejected from merging clumps are depleted in the end-result stellar clusters, which harbour a top-heavy stellar mass function.

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The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

Grasha

Calzetti

Adamo

et al. 2018

Monthly Notices of the Royal Astronomical Society

110

105

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We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the timescale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median ages for clusters associated with clouds is 4 Myr whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After ∼6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50-100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with α = −0.28 ± 0.04, than the GMCs (α = −0.09 ± 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few percent, is comparable (α = −0.35 ± 0.05) to that of the clusters. We find a galactocentric-dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment.

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Lessons from the Local Group

Cited by 4 publications

References 754 publications

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

Hubble–Lemaître fragmentation and the path to equilibrium of merger-driven cluster formation

The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

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