What drives galactic magnetism?

Chyży, K. T.; Sridhar, S. S.; Jurusik, W.

doi:10.1051/0004-6361/201730690

Cited by 13 publications

(12 citation statements)

References 61 publications

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“…Relatively flat spectra for dwarf galaxies have already been noticed by Klein et al (2018) and interpreted as low CR confinement in low-mass galaxies. Considerably lower synchrotron components, and therefore systematically weaker magnetic fields, have recently also been found in late-type spiral galaxies, suggesting that a similar process could be at work in those objects as well (Chyży et al 2017). Our results indicate that, apart from these trends that depend on galaxy properties generally associated with different morphological types, the spectral curvature (∆α) does not correlate with galaxy morphology.…”

Section: Namesupporting

confidence: 47%

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Chyży

Jurusik

Piotrowska

et al. 2018

A&A

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Aims. The shape of low-frequency radio continuum spectra of normal galaxies is not well understood, the key question being the role of physical processes such as thermal absorption in shaping them. In this work we take advantage of the LOFAR Multifrequency Snapshot Sky Survey (MSSS) to investigate such spectra for a large sample of nearby star-forming galaxies. Methods. Using the measured 150 MHz flux densities from the LOFAR MSSS survey and literature flux densities at various frequencies we have obtained integrated radio spectra for 106 galaxies characterised by different morphology and star formation rate. The spectra are explained through the use of a three-dimensional model of galaxy radio emission, and radiation transfer dependent on the galaxy viewing angle and absorption processes. Results. Our galaxies' spectra are generally flatter at lower compared to higher frequencies: the median spectral index α low measured between ≈50 MHz and 1.5 GHz is −0.57 ± 0.01 while the high-frequency one α high , calculated between 1.3 GHz and 5 GHz, is −0.77 ± 0.03. As there is no tendency for the highly inclined galaxies to have more flattened low-frequency spectra, we argue that the observed flattening is not due to thermal absorption, contradicting the suggestion of Israel & Mahoney (1990). According to our modelled radio maps for M 51-like galaxies, the free-free absorption effects can be seen only below 30 MHz and in the global spectra just below 20 MHz, while in the spectra of starburst galaxies, like M 82, the flattening due to absorption is instead visible up to higher frequencies of about 150 MHz. Starbursts are however scarce in the local Universe, in accordance with the weak spectral curvature seen in the galaxies of our sample. Locally, within galactic disks, the absorption effects are distinctly visible in M 51-like galaxies as spectral flattening around 100-200 MHz in the face-on objects, and as turnovers in the edge-on ones, while in M 82-like galaxies there are strong turnovers at frequencies above 700 MHz, regardless of viewing angle. Conclusions. Our modelling of galaxy spectra suggests that the weak spectral flattening observed in the nearby galaxies studied here results principally from synchrotron spectral curvature due to cosmic ray energy losses and propagation effects. We predict much stronger effects of thermal absorption in more distant galaxies with high star formation rates. Some influence exerted by the Milky Way's foreground on the spectra of all external galaxies is also expected at very low frequencies.

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Section: Namesupporting

confidence: 47%

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Chyży

Jurusik

Piotrowska

et al. 2018

A&A

Self Cite

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“…5c). The correlation slope (0.27±0.03; see also Table 1) can be compared to the correlation slope (0.21 -0.28) for a sample of low-mass dwarf and Magellanic-type galaxies, normal spirals and several massive starbursts (Chyży, Sridhar & Jurusik 2017). However, as signaled by the upper limit LITTLE things (purple symbols) and XMPs (red symbols) data points (Fig.…”

Section: B -Sfr Relationmentioning

confidence: 96%

Global correlations between the radio continuum, infrared, and CO emissions in dwarf galaxies

Filho

Tabatabaei

Alméida

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Correlations between the radio continuum, infrared and CO emission are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been assembled to explore this extreme regime. The results demonstrate that the properties of dwarf galaxies are not simple extensions of those of more massive galaxies; the different correlations reflect different star-forming conditions and different coupling between the star formation and the various quantities. It is found that dwarfs show increasingly weaker CO and infrared emission for their luminosity, as expected for galaxies with a low dust content, slower reaction rates, and a hard ionizing radiation field. In the higher-luminosity dwarf regime (L 1.4 GHz 10 27 W, where L 1.4 GHz ≃ 10 29 W for a Milky Way star formation rate of ≃1 M ⊙ yr −1 ), the total and nonthermal radio continuum emission appear to adequately trace the star formation rate. A breakdown of the dependence of the (Hα-based) thermal, non-thermal, and, hence, total radio continuum emission on star formation rate occurs below L 1.4 GHz ≃ 10 27 W, resulting in a steepening or downturn of the relations at extreme low luminosity. Below L FIR ≃ 10 36 W ≃ 3 × 10 9 L ⊙ , the infrared emission ceases to adequately trace the star formation rate. A lack of a correlation between the magnetic field strength and the star formation rate in low star formation rate dwarfs suggests a breakdown of the equipartition assumption. As extremely metal-poor dwarfs mostly populate the low star formation rate and low luminosity regime, they stand out in their infrared, radio continuum and CO properties.

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“…The fact that we find the distortion on both spiral arms would require a detailed MHD study of the effects of tidal forces on galactic disks, and the previous history of the M51 interaction. Van Eck et al (2015) and Chyży et al (2017) found a tight relationship between the specific SFR and the total magnetic field strength, which implies that the process of amplifying magnetic fields in galaxies is mainly driven by small-scale dynamo mechanisms from local SFR (Gressel et al 2008a;Schleicher & Beck 2013). The results from Chyży et al (2017) show that the total magnetic field is correlated with the density of the cold molecular gas (H 2 ) but not with the warm diffuse H I interstellar medium, a result that is compatible with our findings in Sec.…”

Section: Star-formation and Magnetic Fieldsmentioning

confidence: 92%

Extragalactic Magnetism with SOFIA (Legacy Program) -- I: The magnetic field in the multi-phase interstellar medium of M51

Borlaff,

Lopez-Rodriguez,

Beck

et al. 2021

Preprint

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The recent availability of high resolution far-infrared (FIR) polarization observations of galaxies using HAWC+/SOFIA has facilitated studies of extragalactic magnetic fields in the cold and dense molecular disks. We investigate if any significant structural differences are detectable in the kpc-scale magnetic field of the grand design face-on spiral galaxy M51 when traced within the diffuse (radio) and the dense and cold (FIR) interstellar medium (ISM). Our analysis reveals a complex scenario where radio and FIR polarization observations do not necessarily trace the same magnetic field structure. We find that the magnetic field in the arms is wrapped tighter at 154 µm than at 3 and 6 cm; statistically significant lower values for the magnetic pitch angle are measured at FIR in the outskirts (R ≥ 7 kpc) of the galaxy. This difference is not detected in the interarm region. We find strong correlations of the polarization fraction and total intensity at FIR and radio with the gas column density and 12 CO(1-0) velocity dispersion. We conclude that the arms show a relative increase of small-scale turbulent B-fields at regions with increasing column density and dispersion velocities of the molecular gas. No correlations are found with HI neutral gas. The star formation rate shows a clear correlation with the radio polarized intensity, which is not found in FIR, pointing to a small-scale dynamo driven B-field amplification scenario. This work shows that multi-wavelength polarization observations are key to disentangling the interlocked relation between star formation, magnetic fields, and gas kinematics in the multi-phase ISM.

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What drives galactic magnetism?

Cited by 13 publications

References 61 publications

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Global correlations between the radio continuum, infrared, and CO emissions in dwarf galaxies

Extragalactic Magnetism with SOFIA (Legacy Program) -- I: The magnetic field in the multi-phase interstellar medium of M51

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