Global Simulations of the Magnetic Field Evolution in Barred Galaxies Under the Influence of the Cosmic-Ray-Driven Dynamo

Kulpa-Dybeł, K.; Otmianowska-Mazur, K.; Kulesza-Żydzik, Barbara; Hanasz, M.; Kowal, Grzegorz; Wóltański, Dominik; Kowalik, Kacper

doi:10.1088/2041-8205/733/2/l18

Cited by 41 publications

(47 citation statements)

References 17 publications

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“…The larger the SNR, the faster the growth rate, but excessive supernova activity can suppress the dynamo action. Hanasz et al (2009b) demonstrated cosmic-ray-driven dynamo action via global disk spiral galaxies, and Kulpa-Dybeł et al (2011) confirmed the result for barred galaxies. They found that the azimuthal magnetic flux grows on a time-scale of about 270 Myr.…”

Section: Introductionsupporting

confidence: 60%

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Siejkowski

Otmianowska-Mazur

Soida

et al. 2014

A&A

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Context. Star-forming dwarf galaxies can be seen as the local proxies of the high-redshift building blocks of more massive galaxies according to the current paradigm of the hierarchical galaxy formation. They are low-mass objects, and therefore their rotation speed is very low. Several galaxies are observed to show quite strong magnetic fields. These cases of strong ordered magnetic fields seem to correlate with a high, but not extremely high, star formation rate. Aims. We investigate whether these magnetic fields could be generated by the cosmic-ray-driven dynamo. The environment of a dwarf galaxy is unfavourable for the large-scale dynamo action because of the very slow rotation that is required to create the regular component of the magnetic field. Methods. We built a 3D global model of a dwarf galaxy that consists of two gravitational components: the stars and the dark-matter halo described by the purely phenomenological profile proposed previously. We solved a system of magnetohydrodynamic equations that include an additional cosmic-ray component described by the fluid approximation. Results. We found that the cosmic-ray-driven dynamo can amplify the magnetic field with an exponential growth rate. The e-folding time is correlated with the initial rotation speed. The final mean value of the azimuthal flux for our models is on the order of few µG and the system reaches its equipartition level. The results indicate that the cosmic-ray-driven dynamo is a process that can explain the magnetic fields in dwarf galaxies.

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Section: Introductionsupporting

confidence: 60%

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Siejkowski

Otmianowska-Mazur

Soida

et al. 2014

A&A

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“…We made similar kinematical and dynamical assumptions to those in Kulpa-Dybeł et al (2011). The CR-driven dynamo models of a barred galaxy were solved numerically in a 3D computational box with the size of L x = L y = 30 kpc and L z = 7 kpc.…”

Section: Galactic Disk Modelmentioning

confidence: 99%

“…Next, a star can explode as an SN, releasing magnetized material that spreads into the ISM. Rees (1987) suggested that Crab-type SNe remnants have fields of the order of 10 −4 G. He also estimated that at an early stage in galactic evolution there could have been as much as 10 6 randomly oriented SNe remnants similar to the Crab Nebula, giving rise to quite substantial seed fields of the order of 10 −9 G. The recent simulations by Hanasz et al (2009b) and Kulpa-Dybeł et al (2011) have shown that small-scale magnetic fields of stellar origin can be amplified exponentially by the CR driven dynamo up to the observed values, which means that SNe explosions can produce a sufficiently strong seed field for the CR dynamo action. Dubois & Teyssier (2010) did 3D MHD calculations of an isolated dwarf galaxy that had been formed self-consistently inside a cooling halo.…”

Section: Introductionmentioning

confidence: 99%

“…However, the classic kinematic dynamo gives a rather long timescale of magnetic field amplification for galaxies, about 10 9 yr, which is too long to account for strong magnetic fields in high-redshift galaxies beyond z = 1 (Berezinski et al 1990). A faster amplification is possible when the cosmic-ray (CR) driven dynamo (Parker 1992;Hanasz & Lesch 2003;Hanasz et al 2006Hanasz et al , 2009aKulpa-Dybeł et al 2011) is applied, involving three principal effects: first, the CR energy is continuously supplied by supernovae (SNe) remnants to the galactic disk, which became turbulent through buoyancy of magnetic field due to CRs; second, the fast turbulent magnetic reconnection (Lazarian & Vishniac 1999;Kowal et al 2009Kowal et al , 2012Hanasz et al 2004) allows smallscale loops of magnetic field to merge into large-scale coherent structures in the limit of vanishing resistivity; and third, the differential rotation leads to generating a toroidal magnetic field component from the poloidal one. However, every dynamo requires a seed field.…”

Section: Introductionmentioning

confidence: 99%

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The effect of supernova rate on the magnetic field evolution in barred galaxies

Kulpa-Dybeł

Nowak

Otmianowska-Mazur

et al. 2015

A&A

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Context. For the first time, our magnetohydrodynamical numerical calculations provide results for a three-dimensional model of barred galaxies involving a cosmic-ray driven dynamo process that depends on star formation rates. Furthermore, we argue that the cosmic-ray driven dynamo can account for a number of magnetic features in barred galaxies, such as magnetic arms observed along the gaseous arms, magnetic arms in the inter-arm regions, polarized emission that is at the strongest in the central part of the galaxy, where the bar is situated, polarized emission that forms ridges coinciding with the dust lanes along the leading edges of the bar, as well as their very strong total radio intensity. Aims. Our numerical model probes what kind of physical processes could be responsible for the magnetic field topology observed in barred galaxies (modes, etc.). We compare our modelled results directly with observations, constructing models of high-frequency (Faraday rotation-free) polarized radio emission maps out of the simulated magnetic field and cosmic ray pattern in our modeled galaxy. We also take the effects of projection into account as well as the limited resolution. Methods. We applied global 3D numerical calculations of a cosmic-ray driven dynamo in barred galaxies with different physical input parameters such as the supernova (SN) rate. Results. Our simulation results lead to the modelled magnetic field structure similar to the one observed on the radio maps of barred galaxies. Moreover, they cast new light on a number of properties in barred and spiral galaxies, such as fast exponential growth of the total magnetic energy to the present values. The quadrupole modes of magnetic field are often identified in barred galaxies, but the dipole modes (e.g., in NGC 4631) are found very seldom. In our simulations the quadrupole configuration dominates and the dipole configuration only appears once in the case of model S100, apparently as a consequence of the choice of the random number seed. Synthetic radio maps of our models display X-type structure similar to what is observed in real galaxies. Conclusions. We conclude that a cosmic-ray driven dynamo process in barred galaxies can amplify magnetic fields efficiently. The fastest rate of magnetic field increase is 195 yr for a SN frequency of 1/50 yr −1 .The obtained strength of magnetic field corresponds to the observational values (a few μG in spiral arms). The polarization and rotation measure maps also agree with observations. We found the effect of shifting magnetic arms in 4 models (out of the sample of 5).

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“…The latter type of model is much less demanding of computing resources, and readily allows extensive exploration of parameter space, and also the study of phenomena such as large-scale gas streaming in A&A 566, A40 (2014) barred galaxies (e.g. Moss 1998;Moss et al 1998Moss et al , 2001Moss et al , 2007Kulpa-Dybel et al 2011;Kim & Stone 2012), and the effects of spiral arms on dynamo action (Shukurov 1998;Moss 1998;Moss et al 1998Chamandy et al 2013a,b). There are also many studies of the effects of externally driven gas flows on the gas content of galaxies (e.g.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of magnetic fields arising from galactic encounters

Moss

Sokoloff

Beck

et al. 2014

A&A

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Context. Galactic encounters are usually marked by a substantial increase in synchrotron emission of the interacting galaxies when compared with the typical emission from similar non-interacting galaxies. This increase is believed to be associated with an increase in the star formation rate and the turbulent magnetic fields resulting from the encounter, while the regular magnetic field is usually believed to decrease as a result of the encounter. Aims. We attempt to verify these expectations. Methods. We consider a simple, however rather realistic, mean-field galactic dynamo model where the effects of small-scale generation are represented by random injections of magnetic field resulting from star forming regions. We represent an encounter by the introduction of large-scale streaming velocities and by an increase in small-scale magnetic field injections. The latter describes the effect of an increase in the star formation rate caused by the encounter. Results. We demonstrate that large-scale streaming, with associated deviations in the rotation curve, can result in an enhancement of the anisotropic turbulent (ordered) magnetic field strength, mainly along the azimuthal direction. This leads to a significant temporary increase of the total magnetic energy during the encounter; the representation of an increase in star formation rate has an additional strong effect. In contrast to expectations, the large-scale (regular) magnetic field structure is not significantly destroyed by the encounter. It may be somewhat weakened for a relatively short period, and its direction after the encounter may be reversed. Conclusions. The encounter causes enhanced total and polarized emission without increase in the regular magnetic field strength. The increase in synchrotron emission caused by the large-scale streaming can be comparable to the effect of the increase in the star formation rate, depending on the choice of parameters. The effects of the encounter on the total magnetic field energy last only slightly longer than the duration of the encounter (ca. 1 Gyr). However, a long-lasting field reversal of the regular magnetic field may result.

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Global Simulations of the Magnetic Field Evolution in Barred Galaxies Under the Influence of the Cosmic-Ray-Driven Dynamo

Cited by 41 publications

References 17 publications

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

The effect of supernova rate on the magnetic field evolution in barred galaxies

Enhancement of magnetic fields arising from galactic encounters

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