Radio haloes in nearby galaxies modelled with 1D cosmic ray transport using spinnaker

Heesen, V.; Krause, M.; Beck, Rainer; Adebahr, B.; Bomans, D. J.; Carretti, E.; Dumke, M.; Heald, G.; Irwin, Judith A.; Koribalski, B. S.; Mulcahy, D. D.; Westmeier, T.; Dettmar, R.‐J.

doi:10.1093/mnras/sty105

Cited by 68 publications

(109 citation statements)

References 118 publications

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“…(v) The advection speed of the radio emitting outflowing gas scaled with SFR as v adv ∝ Σ 1/3 SFR . Such a scaling relation has been observed previously (e.g., Heesen et. al.…”

Section: Discussionsupporting

confidence: 85%

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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“…(v) The advection speed of the radio emitting outflowing gas scaled with SFR as v adv ∝ Σ 1/3 SFR . Such a scaling relation has been observed previously (e.g., Heesen et. al.…”

Section: Discussionsupporting

confidence: 85%

Radio haloes of star-forming galaxies

Vijayan

Nath

Sharma

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…So w = 2 implies only a modest outflow. A value more like w = 5−10 would be required to imitate the outflow velocities inferred elsewhere (Heesen et al 2018). As may be expected, these tend to draw the magnetic field up into the halo and erase the parity change (Henriksen 2018).…”

Section: Outflow or Accretion In The Patternmentioning

confidence: 90%

Evolving galactic dynamos and fits to the reversing rotation measures in the halo of NGC 4631

Woodfinden

Henriksen

Irwin

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Rotation measure (RM) synthesis maps of NGC 4631 show remarkable sign reversals with distance from the minor axis in the northern halo of the galaxy on kpc scales. To explain this new phenomenon, we solve the dynamo equations under the assumption of scale invariance and search for rotating logarithmic spiral solutions. Solutions for velocity fields representing accretion onto the disk, outflow from the disk, and rotationonly in the disk are found that produce RM with reversing signs viewed edge-on. Model RM maps are created for a variety of input parameters using a Faraday screen and are scaled to the same amplitude as the observational maps. Residual images are then made and compared to find a best fit. Solutions for rotation-only, i.e. relative to a pattern uniform rotation, did in general, not fit the observations of NGC 4631 well. However, outflow models did provide a reasonable fit to the magnetic field. The best results for the specific region that was modelled in the northern halo are found with accretion. Since there is abundant evidence for both winds and accretion in NGC 4631, this modelling technique has the potential to distinguish between the dominant flows in galaxies.

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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%

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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Radio haloes in nearby galaxies modelled with 1D cosmic ray transport using spinnaker

Cited by 68 publications

References 118 publications

Radio haloes of star-forming galaxies

Radio haloes of star-forming galaxies

Evolving galactic dynamos and fits to the reversing rotation measures in the halo of NGC 4631

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

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