Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

Heesen, V.; Buie, Edward; Huff, C. J.; Perez, Lucia A.; Woolsey, J. G.; Rafferty, D. A.; Basu, Aritra; Beck, Rainer; Brinks, E.; Horellou, C.; Scannapieco, Evan; Brüggen, M.; Dettmar, R.‐J.; Sendlinger, K.; Nikiel-Wroczyński, B.; Chyży, K. T.; Best, P. N.; Heald, G.; Paladino, R.

doi:10.1051/0004-6361/201833905

Cited by 30 publications

(58 citation statements)

References 71 publications

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“…In the Milky Way, cosmic-ray abundance measurements, such as the boron to carbon ratio, give diffusion coefficients D 0 ≡ D(1 GeV) of the order of 10 28 cm 2 s −1 (e.g. Korsmeier & Cuoco 2016), with similar values found in external galaxies for the CR e − from spectral ageing (Heesen et al 2019). These values are a factor of ∼ 10 7 larger than for the Bohm limit.…”

Section: Predictionsmentioning

confidence: 81%

Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

Vollmann

Heesen

Shimwell

et al. 2020

Monthly Notices of the Royal Astronomical Society

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ABSTRACT Dwarf galaxies are dark matter (DM) dominated and therefore promising targets for the search for weakly interacting massive particles (WIMPs), which are well-known candidates for DM. The annihilation of WIMPs produces ultrarelativistic cosmic ray electrons and positrons that emit synchrotron radiation in the presence of magnetic fields. For typical magnetic field strengths (few μG) and $\mathcal {O}$(GeV–TeV) WIMP masses, this emission peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the Low-Frequency Array to derive constraints on the annihilation cross-section of WIMPs into primary electron–positron and other fundamental particle–antiparticle pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, thus requiring a non-zero magnetic field strength with small-scale structure. In particular, by adopting magnetic field strengths of $\mathcal {O}(1\, \mu$G) and diffusion coefficients $\sim \!10^{27}~\rm cm^2\, s^{-1}$, we obtain limits that are comparable with those set by the Fermi Large Area Telescope using gamma-ray observations of this particular galaxy. Assuming s-wave annihilation and WIMPs making up 100 per cent of the DM density, our benchmark limits exclude several thermal WIMP realizations in the [2, 20]-GeV mass range. We caution, however, that our limits for the cross-section are subject to enormous uncertainties that we also quantitatively assess. In particular, variations on the propagation parameters or on the DM halo can shift our limits up by several orders of magnitude (in the pessimistic scenario).

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Section: Predictionsmentioning

confidence: 81%

Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

Vollmann

Heesen

Shimwell

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…As can be seen, the diffusion approximation results in flatter CRe − number density profiles in the inner parts of the galaxy but steeper in the outskirts. The corresponding radio intensity profiles can be thus better described as Gaussian rather than as exponential functions (Heesen et al 2019a). The models presented in Fig.…”

Section: Diffusionmentioning

confidence: 99%

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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“…We want to see if we can find evidence for such a local behaviour. In addition, the cosmic ray electron source term Q(E) should be directly linked to the star formation distribution, rather than the far-infrared emission distribution (see, e.g., Heesen et al 2014Heesen et al , 2019.…”

Section: Introductionmentioning

confidence: 99%

Deciphering the radio star formation correlation on kpc scales

Vollmer

Soida

Beck

et al. 2020

A&A

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One of the tightest correlations in astronomy is the relation between the integrated radio continuum and the far-infrared emission. Within nearby galaxies, variations in the radio-FIR correlation have been observed, mainly because the cosmic ray electrons migrate before they lose their energy via synchrotron emission or escape. The major cosmic ray electron transport mechanisms within the plane of galactic disks are diffusion and streaming. A predicted radio continuum map can be obtained by convolving the map of comic ray electron sources, represented by that of the star formation, with adaptive Gaussian and exponential kernels. The ratio between the smoothing lengthscales at 6 cm and 20 cm can be used to distinguish between diffusion and streaming as the dominant transport mechanism. The dependence of the smoothing lengthscale on the star formation rate bares information on dependence of the magnetic field strength or the ratio between the ordered and turbulent magnetic field strengths on star formation. Star formation maps of eight rather face-on local and Virgo cluster spiral galaxies were constructed from Spitzer and Herschel infrared and GALEX UV observations. These maps were convolved with adaptive Gaussian and exponential smoothing kernels to obtain model radio continuum emission maps. It is found that in asymmetric ridges of polarized radio continuum emission the total power emission is enhanced with respect to the star formation rate. At a characteristic star formation rate ofΣ * = 8 × 10 −3 M yr −1 kpc −2 the typical lengthscale for the transport of cosmic ray electrons is l = 0.9 ± 0.3 kpc at 6 cm and l = 1.8 ± 0.5 kpc at 20 cm. Perturbed spiral galaxies tend to have smaller lengthscales. This is a natural consequence of the enhancement of the magnetic field caused by the interaction. The discrimination between the two cosmic ray electron transport mechanisms, diffusion and streaming, is based on (i) the convolution kernel (Gaussian or exponential), (ii) the dependence of the smoothing kernel on the local magnetic field and hence on the local star formation rate, (iii) the ratio between the two smoothing lengthscales via the frequency-dependence of the smoothing kernel, and (iv) the dependence of the smoothing kernel on the ratio between the ordered and the turbulent magnetic field. Based on our empirical results, methods (i) and (ii) cannot be used to determine the cosmic ray transport mechanism. Important asymmetric large-scale residuals and a local dependence of the smoothing length on B ord /B turb are most probably responsible for the failure of method (i) and (ii), respectively. On the other hand, the classifications based on l6cm/l20cm (method iii) and B ord /B turb (method iv) are well consistent and complementary. We argue that in the six Virgo spiral galaxies the turbulent magnetic field is globally enhanced in the disk. Therefore, the regions where the magnetic field is independent of the star formation rate are more common. In addition, B ord /B turb decreases leading to a diffusion lengths...

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Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

Cited by 30 publications

References 71 publications

Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

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

Deciphering the radio star formation correlation on kpc scales

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