Launching Cosmic-Ray-Driven Outflows From the Magnetized Interstellar Medium

Girichidis, Philipp; Naab, Thorsten; Walch, Stefanie; Hanasz, M.; Low, Mordecai–Mark Mac; Ostriker, Jeremiah P.; Gatto, Andrea; Peters, Thomas; Wünsch, Richard; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul; Baczynski, Christian

doi:10.3847/2041-8205/816/2/l19

Cited by 233 publications

(237 citation statements)

References 48 publications

(56 reference statements)

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“…Recent simulations show CRs are promising candidates to drive galactic scale outflows, with a mass loading around 0.5 (Uhlig et al 2012;Hanasz et al 2013;Booth et al 2013;Salem & Bryan 2014). Recent high-resolution, local simulations indicate that for the solar neighbourhood, both CRs and SN thermal feedback can drive an outflow with mass loading around unity (Girichidis et al 2016a;Simpson et al 2016). CR-driven outflows are cooler, slower, and smoother than the thermally-driven ones.…”

Section: Comparison With Other Workmentioning

confidence: 99%

Quantifying Supernovae-driven Multiphase Galactic Outflows

Li¹,

Bryan²,

Ostriker³

2017

ApJ

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133

119

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Galactic outflows are ubiquitously observed in star-forming disk galaxies and are critical for galaxy formation. Supernovae (SNe) play the key role in driving the outflows, but there is no consensus as to how much energy, mass and metal they can launch out of the disk. We perform 3D, high-resolution hydrodynamic simulations to study SNe-driven outflows from stratified media. Assuming SN rate scales with gas surface density Σ gas as in the Kennicutt-Schmidt (KS) relation, we find the mass loading factor, η m , defined as the mass outflow flux divided by the star formation surface density, decreases with increasing Σ gas as η m ∝ Σ −0.61 gas . Approximately Σ gas 50M / pc 2 marks when η m 1. About 10-50% of the energy and 40-80% of the metals produced by SNe end up in the outflows. The tenuous hot phase (T > 3×10 5 K), which fills 60-80% of the volume at mid-plane, carries the majority of the energy and metals in outflows. We discuss how various physical processes, including vertical distribution of SNe, photoelectric heating, external gravitational field and SN rate, affect the loading efficiencies. The relative scale height of gas and SNe is a very important factor in determining the loading efficiencies.

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Section: Comparison With Other Workmentioning

confidence: 99%

Quantifying Supernovae-driven Multiphase Galactic Outflows

Li¹,

Bryan²,

Ostriker³

2017

ApJ

Self Cite

133

119

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“…However, this is much more challenging owing to the complicated behavior of CR propagation which depends on the configuration of the magnetic fields and some uncertainties in its propagation mechanisms (Uhlig et al 2012;Hanasz et al 2013;Girichidis et al 2016a;Simpson et al 2016). A fully self-consistent treatment of the CR ionization heating therefore requires substantial further investigation.…”

Section: Cosmic Ray Ionizationmentioning

confidence: 99%

Variable interstellar radiation fields in simulated dwarf galaxies: supernovae versus photoelectric heating

Naab

Glover

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present high-resolution hydrodynamical simulations of isolated dwarf galaxies including self-gravity, non-equilibrium cooling and chemistry, interstellar radiation fields (IRSF) and shielding, star formation, and stellar feedback. This includes spatially and temporally varying photoelectric (PE) heating, photoionization, resolved supernova (SN) blast waves and metal enrichment. A new flexible method to sample the stellar initial mass function allows us to follow the contribution to the ISRF, the metal output and the SN delay times of individual massive stars. We find that SNe play the dominant role in regulating the global star formation rate, shaping the multi-phase interstellar medium (ISM) and driving galactic outflows. Outflow rates (with massloading factors of a few) and hot gas fractions of the ISM increase with the number of SNe exploding in low-density environments where radiative energy losses are low. While PE heating alone can suppress star formation slightly more (a factor of a few) than SNe alone can do, it is unable to drive outflows and reproduce the multi-phase ISM that emerges naturally when SNe are included. These results are in conflict with recent results of Forbes et al. who concluded that PE heating is the dominant process suppressing star formation in dwarfs, about an order of magnitude more efficient than SNe. Potential origins for this discrepancy are discussed. In the absence of SNe and photoionization (mechanisms to disperse dense clouds), the impact of PE heating is highly overestimated owing to the (unrealistic) proximity of dense gas to the radiation sources. This leads to a substantial boost of the infrared continuum emission from the UV-irradiated dust and a far infrared line-to-continuum ratio too low compared to observations. Though sub-dominant in regulating star formation, the ISRF controls the abundance of molecular hydrogen via photodissociation.

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“…We stress that our simulations do not include the cosmic rays, which likely contribute to support the galactic disc against gravity. In particular Girichidis et al (2016) have recently performed simulations which suggest that this cosmic rays could indeed have a significant contribution, mainly because they dissipate less easily that the hot gas produced by supernova explosions. Definite conclusions are, however, prevented given the difficulties of accurately measure this scale height.…”

Section: Density and Pressure Profilesmentioning

confidence: 99%

Structure distribution and turbulence in self-consistently supernova-driven ISM of multiphase magnetized galactic discs

Iffrig

Hennebelle

2017

A&A

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Context. Galaxy evolution and star formation are two multi-scale problems tightly linked to each other. Aims. We aim to describe simultaneously the large-scale evolution widely induced by the feedback processes and the details of the gas dynamics that controls the star formation process through gravitational collapse. This is a necessary step in understanding the interstellar cycle, which triggers galaxy evolution. Methods. We performed a set of three-dimensional high-resolution numerical simulations of a turbulent, self-gravitating and magnetized interstellar medium within a 1 kpc stratified box with supernova feedback correlated with star-forming regions. In particular, we focussed on the role played by the magnetic field and the feedback on the galactic vertical structure, the star formation rate (SFR) and the flow dynamics. For this purpose we have varied their respective intensities. We extracted properties of the dense clouds arising from the turbulent motions and compute power spectra of various quantities. Results. Using a distribution of supernovae sufficiently correlated with the dense gas, we find that supernova explosions can reproduce the observed SFR, particularly if the magnetic field is on the order of a few µG. The vertical structure, which results from a dynamical and an energy equilibrium is well reproduced by a simple analytical model, which allows us to roughly estimate the efficiency of the supernovae in driving the turbulence in the disc to be rather low, of the order of 1.5%. Strong magnetic fields may help to increase this efficiency by a factor of between two and three. To characterize the flow we compute the power spectra of various quantities in 3D but also in 2D in order to account for the stratification of the galactic disc. We find that within our setup, the compressive modes tend to dominate in the equatorial plane, while at about one scale height above it, solenoidal modes become dominant. We measured the angle between the magnetic and velocity fields and we conclude that they tend to be well aligned particularly at high magnetization and lower feedback. Finally, the dense structures present scaling relations that are reminiscent of the observational ones. The virial parameter is typically larger than 10 and shows a large spread of masses below 1000 M . For masses larger than 10 4 M , its value tends to a few. Conclusions. Using a relatively simple scheme for the supernova feedback, which is self-consistently proportional to the SFR and spatially correlated to the star formation process, we reproduce a stratified galactic disc that presents reasonable scale height, SFR as well as a cloud distribution with characteristics close to the observed ones.

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Launching Cosmic-Ray-Driven Outflows From the Magnetized Interstellar Medium

Cited by 233 publications

References 48 publications

Quantifying Supernovae-driven Multiphase Galactic Outflows

Quantifying Supernovae-driven Multiphase Galactic Outflows

Variable interstellar radiation fields in simulated dwarf galaxies: supernovae versus photoelectric heating

Structure distribution and turbulence in self-consistently supernova-driven ISM of multiphase magnetized galactic discs

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