Chang-Es

Krause, M.; Irwin, Judith A.; Wiegert, Theresa; Miskolczi, A.; Damas-Segovia, Ancor; Beck, Rainer; Li, Jiangtao; Heald, G.; Müller, P.; Stein, Y.; Rand, Richard J.; Heesen, V.; Walterbos, R. A. M.; Dettmar, R.‐J.; Vargas, Carlos J.; English, Jayanne; Murphy, E. J.

doi:10.1051/0004-6361/201731991

Cited by 84 publications

(194 citation statements)

References 21 publications

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“…Clearly, the extra-planar radio emission is related to the distribution of star formation sites in the disk. This has been confirmed by Krause et. al.…”

Section: Introductionsupporting

confidence: 81%

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Radio haloes of star-forming galaxies

Vijayan

Nath

Sharma

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We study the synchrotron radio emission from extra-planar regions of star forming galaxies. We use ideal magneto-hydrodynamical (MHD) simulations of a rotating Milky Way-type disk galaxy with distributed star formation sites for three star formation rates (SFRs) (0.3, 3, 30 M yr −1 ). From our simulations, we see emergence of galactic-scale magnetised outflows, carrying gas from the disk. We compare the morphology of the outflowing gas with hydrodynamic (HD) simulations. We look at the spatial distribution of magnetic field in the outflows. Assuming that a certain fraction of gas energy density is converted into cosmic ray energy density, and using information about the magnetic field, we obtain synchrotron emissivity throughout the simulation domain. We generate the surface brightness maps at a frequency of 1.4 GHz. The outflows are more extended in the vertical direction than radial and hence have an oblate shape. We further find that the matter right behind the outer shock, shines brighter in these maps than that above or below. To understand whether this feature can be observed, we produce vertical intensity profiles. We convolve the vertical intensity profile with the typical beam sizes of radio telescopes, for a galaxy located at 10 Mpc (similar to NGC 891) in order to estimate the radio scale height to compare with observations. We find that for our SFRs this feature will lie below the RMS noise limit of instruments. The radio scale height is found to be ∼ 300 − 1200 pc , depending on the resolution of the telescope. We relate the advection speed of the outer shock with the surface density of star formation as v adv ∝ Σ 0.3 SFR , which is consistent with earlier observations and analytical estimates.

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“…Clearly, the extra-planar radio emission is related to the distribution of star formation sites in the disk. This has been confirmed by Krause et. al.…”

Section: Introductionsupporting

confidence: 81%

“…In Figure 10 we show the time-averaged radio emission scale height for three star formation rates. Krause et. al.…”

Section: Scale Height Of Emissionmentioning

confidence: 99%

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Radio haloes of star-forming galaxies

Vijayan

Nath

Sharma

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Edge-on views of most spiral galaxies reveal a thin and a thick disc in synchrotron emission with exponential scale heights of a few 100 pc and a few kpc, respectively [200,201]. Thick radio discs are also called "radio halos".…”

Section: Observationsmentioning

confidence: 99%

“…M 31) have only a thin disc in synchrotron emission. In most galaxies, the synchrotron scale height of the halo is H syn = 1 − 2 kpc and the disc scale length is R syn = 3 − 6 kpc [201].…”

Section: Observationsmentioning

confidence: 99%

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

et al. 2019

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Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Further, we measure the velocity dispersion of H I gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

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The radio continuum perspective on cosmic-ray transport in external galaxies

Heesen

2021

Astrophys Space Sci

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Radio continuum observations of external galaxies provide us with an excellent outside view on the distribution of cosmic-ray electrons in the disc and halo. In this review, we summarise the current state of what we have learned from modelling such observations with cosmic-ray transport, paying particular attention to the question to what extent we can exploit radio haloes when studying galactic winds. We have developed the user-friendly framework spinnaker to model radio haloes with either pure advection or diffusion, allowing us to study both diffusion coefficients and advection speeds in nearby galaxies. Using these models, we show that we can identify galaxies with winds using both morphology and radio spectral indices of radio haloes. Advective radio haloes are ubiquitous, indicating that already fairly low values of the star formation rate (SFR) surface density ($\Sigma_{ \mathrm{SFR}}$ Σ SFR ) can trigger galactic winds. The advection speeds scale with SFR, $\Sigma_{\mathrm{SFR}}$ Σ SFR , and rotation speed as expected for stellar feedback-driven winds. Accelerating winds are in agreement with our radio spectral index data, but this is sensitive to the magnetic field parametrisation, so that constant wind speeds cannot be ruled out either. The question to what extent cosmic rays can be a driving force behind winds is still an open issue and we discuss only in passing how a simple iso-thermal wind model could fit our data. Nevertheless, the comparison with inferences from observations and theory looks promising with radio continuum offering a complementary view on galactic winds. We finish with a perspective on future observations and challenges lying ahead.

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Chang-Es

Cited by 84 publications

References 21 publications

Radio haloes of star-forming galaxies

Radio haloes of star-forming galaxies

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

The radio continuum perspective on cosmic-ray transport in external galaxies

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