Cloud-cloud collisions and triggered star formation

Fukui, Yasuo; Habe, Asao; Inoue, Tsuyoshi; Enokiya, Rei; Tachihara, Kengo

doi:10.48550/arxiv.2009.05077

Cited by 6 publications

(11 citation statements)

References 124 publications

(196 reference statements)

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“…According 1 The threshold density for the sink formation is 5.6 × 10 4 cm −3 . This value is much lower than that used in our previous studies, because we do not employ the adaptive mesh refinement in the present study to the shock jump condition: ρ 0 v 2 0 ∼ B 2 1 /(8π) (e.g., §4.1 of Fukui et al 2020), the compression ratio is given by…”

Section: High Shock Velocity Casementioning

confidence: 85%

Classification of Filament Formation Mechanisms in Magnetized Molecular Clouds

Abe

Inoue

Inutsuka

et al. 2021

ApJ

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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 of filament formation. We focus on the influences of shock velocity and turbulence on the formation mechanism and identified three different mechanisms for the filament formation. The results indicate that when the shock is fast, at shock velocity v sh ≃ 7 km s−1, the gas flows driven by the curved shock wave create filaments irrespective of the presence of turbulence and self-gravity. However, at a slow shock velocity v sh ≃ 2.5 km s−1, the compressive flow component involved in the initial turbulence induces filament formation. When both the shock velocities and turbulence are low, the self-gravity in the shock-compressed sheet becomes important for filament formation. Moreover, we analyzed the line-mass distribution of the filaments and showed that strong shock waves can naturally create high-line-mass filaments such as those observed in the massive star-forming regions in a short time. We conclude that the dominant filament formation mode changes with the velocity of the shock wave triggering the filament formation.

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Section: High Shock Velocity Casementioning

confidence: 85%

Classification of Filament Formation Mechanisms in Magnetized Molecular Clouds

Abe

Inoue

Inutsuka

et al. 2021

ApJ

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“…These same streaming motions can also redistribute the gas, fuel star formation in the inner parts of the galaxy, or even trigger nuclear starbursts (e.g, Kenney et al 1992;Sakamoto et al 1999;Sheth et al 2005;Schmidt et al 2016). Collisions between gas clouds may also trigger star formation (e.g., Tan 2000;Inoue & Fukui 2013;Fukui et al 2020).…”

Section: Key Physics At or Near Cloud Scalesmentioning

confidence: 99%

PHANGS-ALMA: Arcsecond CO(2-1) Imaging of Nearby Star-Forming Galaxies

Leroy,

Schinnerer,

Hughes

et al. 2021

Preprint

101

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We present PHANGS-ALMA, the first survey to map CO J = 2 → 1 line emission at ∼ 1 ∼ 100 pc spatial resolution from a representative sample of 90 nearby (d 20 Mpc) galaxies that lie on or near the z = 0 "main sequence" of star-forming galaxies. CO line emission traces the bulk distribution of molecular gas, which is the cold, star-forming phase of the interstellar medium. At the resolution achieved by PHANGS-ALMA, each beam reaches the size of a typical individual giant molecular cloud (GMC), so that these data can be used to measure the demographics, life-cycle, and physical state of molecular clouds across the population of galaxies where the majority of stars form at z = 0. This paper describes the scientific motivation and background for the survey, sample selection, global properties of the targets, ALMA observations, and characteristics of the delivered ALMA data and derived data products. As the ALMA sample serves as the parent sample for parallel surveys with VLT/MUSE, HST, AstroSat, VLA, and other facilities, we include a detailed discussion of the sample selection. We detail the estimation of galaxy mass, size, star formation rate, CO luminosity, and other properties, compare estimates using different systems and provide best-estimate integrated measurements for each target. We also report the design and execution of the ALMA observations, which combine a Cycle 5 Large Program, a series of smaller programs, and archival observations. Finally, we present the first 1 resolution atlas of CO emission from nearby galaxies and describe the properties and contents of the first PHANGS-ALMA public data release.1. INTRODUCTION This paper presents PHANGS-ALMA, an Atacama Large Millimeter/submillimeter Array (ALMA) survey aimed at studying the physics of molecular gas across the nearby galaxy population. PHANGS-ALMA is a key component of the multiwavelength observational campaign conducted by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) project 1 . Combining a Cycle 5 ALMA Large Program, a suite of smaller programs, and data from the ALMA archive, PHANGS-ALMA mapped the CO J = 2 → 1 emission, hereafter CO(2-1), from a cleanly-selected sample of 90 of the nearest, ALMA-accessible, massive, star-forming galaxies. The resulting CO(2-1) data have high spatial and spectral resolution, good surface brightness sensitivity, full flux recovery, and good coverage of the area of active star formation in each target.These characteristics make PHANGS-ALMA the first "cloud scale," ∼ 100 pc, survey of molecular gas across a local galaxy sample that is representative of where stars form in the z = 0 universe. Though the data are

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“…At this time (1.1 Myr), the clouds have collided, but there is relatively little fragmentation of the filaments formed from the shock at this point. In the case where the field is perpendicular to the collision, but parallel to the shock, the shock induces an increase in the strength of the field in this direction, as expected for a fast shock (Ryu & Jones 1995;Fukui et al 2020). Theoretically, we would expect the magnetic field component parallel to the shock to increase by the same amount as the density.…”

Section: Magnetic Field and Filamentsmentioning

confidence: 75%

“…Wu et al (2020) also find that less fragmentation occurs in models with stronger fields, and there are fewer stars. Although some studies now explicitly include sink particles (Inoue et al 2018;Fogerty et al 2016;Zamora-Avilés et al 2018;Fukui et al 2020), few investigate the role of magnetic fields on cluster formation.…”

mentioning

confidence: 99%

The properties of clusters, and the orientation of magnetic fields relative to filaments, in magnetohydrodynamic simulations of colliding clouds

Dobbs,

Wurster

2021

Preprint

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We have performed Smoothed Particle Magneto-Hydrodynamics (SPMHD) calculations of colliding clouds to investigate the formation of massive stellar clusters, adopting a timestep criterion to prevent large divergence errors. We find that magnetic fields do not impede the formation of young massive clusters (YMCs), and the development of high star formation rates, although we do see a strong dependence of our results on the direction of the magnetic field. If the field is initially perpendicular to the collision, and sufficiently strong, we find that star formation is delayed, and the morphology of the resulting clusters is significantly altered. We relate this to the large amplification of the field with this initial orientation. We also see that filaments formed with this configuration are less dense. When the field is parallel to the collision, there is much less amplification of the field, dense filaments form, and the formation of clusters is similar to the purely hydrodynamical case. Our simulations reproduce the observed tendency for magnetic fields to be aligned perpendicularly to dense filaments, and parallel to low density filaments. Overall our results are in broad agreement with past work in this area using grid codes.

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Cloud-cloud collisions and triggered star formation

Cited by 6 publications

References 124 publications

Classification of Filament Formation Mechanisms in Magnetized Molecular Clouds

Classification of Filament Formation Mechanisms in Magnetized Molecular Clouds

PHANGS-ALMA: Arcsecond CO(2-1) Imaging of Nearby Star-Forming Galaxies

The properties of clusters, and the orientation of magnetic fields relative to filaments, in magnetohydrodynamic simulations of colliding clouds

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