Simulating radio synchrotron emission in star-forming galaxies: small-scale magnetic dynamo and the origin of the far infrared-radio correlation

Pfrommer, Christoph; Werhahn, Maria; Pakmor, Rüdiger; Girichidis, Philipp; Simpson, Christine M.

doi:10.48550/arxiv.2105.12132

Cited by 7 publications

(9 citation statements)

References 93 publications

(139 reference statements)

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“…While coherent magnetic fields have been observed in distant galaxies, for instance at z = 0.439 as reported in Ref. [86], their generation and evolution are still a subject of ongoing research from a numerical [87,88] as well as an observational [89] point of view. There are indications that large-scale regular galactic magnetic fields require time to form, rendering their existence a feature that is expected for galaxies at z < 1 [90] whereas smallscale turbulent magnetic fields dominate at higher redshifts.…”

Section: The Alps Sub-pev γ-Ray Diffuse Fluxmentioning

confidence: 86%

First constraints on axion-like particles from Galactic sub-PeV gamma rays

Eckner,

Calore

2022

Preprint

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Experimental refinements and technical innovations in the field of extensive air shower telescopes have enabled measurements of Galactic cosmic-ray interactions in the sub-PeV (100 TeV to 1 PeV) range, providing new avenues for the search for new physics and dark matter. For the first time, we exploit sub-PeV (10 TeV -1 PeV) observations of Galactic diffuse gamma rays by Tibet ASγ and HAWC to search for an axion-like-particle (ALP) induced gamma-ray signal directly linked to the origin of the IceCube extragalactic high-energy neutrino flux. Indeed, the production of high-energy neutrinos in extragalatic sources implies the concomitant production of gamma rays at comparable energies. Within the magnetic field of the neutrino emitting sources, gamma rays may efficiently convert into ALPs and escape their host galaxy unattenuated, propagate through intergalactic space, and reconvert into gamma rays in the magnetic field of the Milky Way. Such a scenario creates an all-sky diffuse high-energy gamma-ray signal in the sub-PeV range. Accounting for the guaranteed Galactic astrophysical gamma-ray contributions from cosmic-ray interactions with gas and radiation and from sub-threshold sources, we set competitive upper limits on the photon-ALP coupling constant gaγγ. We find gaγγ < 2.1 × 10 −11 GeV −1 for ALP masses ma ≤ 2 × 10 −7 eV at a 95% confidence level, progressively closing the mass gap towards ADMX limits.

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Section: The Alps Sub-pev γ-Ray Diffuse Fluxmentioning

confidence: 86%

First constraints on axion-like particles from Galactic sub-PeV gamma rays

Eckner,

Calore

2022

Preprint

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“…The galaxy is initialized in a M200 = 10 11 M halo with 10 6 equalmass gas particles particles that are in hydrostatic equilibrium with the dark matter halo. The setup up is similar to those used in previous works (Pakmor et al 2016b;Pfrommer et al 2017bPfrommer et al , 2021Werhahn et al 2021a). The dark matter halo is static and follows the analytic form of an NFW halo with concentration parameter c = 7 (Navarro et al 1997).…”

Section: Simulation Setupmentioning

confidence: 99%

Cosmic ray-driven galactic winds: transport modes of cosmic rays and Alfvén-wave dark regions

Thomas¹,

Pfrommer²,

Pakmor³

2022

Preprint

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Feedback mediated by cosmic rays (CRs) is an important process in galaxy formation. Because CRs are long-lived and because they are transported along magnetic field lines independently of any gas flow, they can efficiently distribute their feedback energy within the galaxy. We present an in-depth investigation of (i) how CRs launch galactic winds from a disc that is forming in a 10 11 M halo and (ii) how CR transport affects the dynamics in a galactic outflow. To this end, we use the Arepo moving-mesh code and model CR transport with the two-moment description of CR hydrodynamics. This model includes the CR interaction with gyroresonant Alfvén waves that enables us to selfconsistently calculate the CR diffusion coefficient and CR transport speeds based on coarse-grained models for plasma physical effects. This delivers insight into key questions such as whether the effective CR transport is streaming-like or diffusive-like, how the CR diffusion coefficient and transport speed change inside the circumgalactic medium (CGM), and to what degree the two-moment approximation is needed to faithfully capture these effects. We find that the CRdiffusion coefficient reaches a steady-state in most environments with the notable exception of our newly discovered Alfvén-wave dark regions where the toroidal wind magnetic field is nearly perpendicular to the CR pressure gradient so that CRs are unable to excite gyroresonant Alfvén waves. However, CR transport itself cannot reach a steady-state and is not well described by either the CR streaming paradigm, the CR diffusion paradigm or a combination of both.

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“…One way to is to include the calorimetric synchrotron fraction 𝜂 of the CRE, so that the semi-calorimetric radio-SFR relation, which takes CRE escape into account, becomes (e.g. Pfrommer et al 2021) :…”

Section: Semi-calorimetric Radio-sfr Relationmentioning

confidence: 99%

Nearby galaxies in LoTSS-DR2: insights into the non-linearity of the radio-SFR relation

Heesen,

Staffehl,

Basu

et al. 2022

Preprint

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Context. Cosmic rays and magnetic fields are key ingredients in galaxy evolution, regulating both stellar feedback and star formation. Their properties can be studied with low-frequency radio continuum observations, free from thermal contamination. Aims. We define a sample of 76 nearby (< 30 Mpc) galaxies, with rich ancillary data in the radio continuum and infrared from the CHANG-ES and KINGFISH surveys, which will be observed with the LOFAR Two-metre Sky Survey (LoTSS) at 144 MHz. Methods. We present maps for 45 of them as part of the LoTSS data release 2 (LoTSS-DR2), where we measure integrated flux densities and study integrated and spatially resolved radio spectral indices. We investigate the radio-SFR relation, using star-formation rates (SFR) from total infrared and H 𝛼 + 24-𝜇m emission.Results. The radio-SFR relation at 144 MHz is clearly super-linear with 𝐿 144 ∝ 𝑆𝐹 𝑅 1.4−1.5 . The mean integrated radio spectral index between 144 and ≈1400 MHz is 𝛼 = −0.56 ± 0.14, in agreement with the injection spectral index for cosmic ray electrons (CRE). However, the radio spectral index maps show a variation of spectral indices with flatter spectra associated with star-forming regions and steeper spectra in galaxy outskirts and, in particular, in extra-planar regions. We found that galaxies with high star-formation rates (SFR) have steeper radio spectra; we find similar correlations with galaxy size, mass, and rotation speed. Conclusions. Galaxies that are larger and more massive are better electron calorimeters, meaning that the CRE lose a higher fraction of their energy within the galaxies. This explains the super-linear radio-SFR relation, with more massive, star-forming galaxies being radio bright. We propose a semi-calorimetric radio-SFR relation, which employs the galaxy mass as a proxy for the calorimetric efficiency.

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Simulating radio synchrotron emission in star-forming galaxies: small-scale magnetic dynamo and the origin of the far infrared-radio correlation

Cited by 7 publications

References 93 publications

First constraints on axion-like particles from Galactic sub-PeV gamma rays

First constraints on axion-like particles from Galactic sub-PeV gamma rays

Cosmic ray-driven galactic winds: transport modes of cosmic rays and Alfvén-wave dark regions

Nearby galaxies in LoTSS-DR2: insights into the non-linearity of the radio-SFR relation

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