ORCID Profile
0000-0003-2030-3394
Current Organisations
Thüringer Landessternwarte Tautenburg
,
Max-Planck-Institut für Radioastronomie
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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Lie Groups, Harmonic and Fourier Analysis | Pure Mathematics | Algebraic and Differential Geometry | Topology
Publisher: Oxford University Press (OUP)
Date: 16-05-2019
Publisher: Springer Science and Business Media LLC
Date: 28-08-2017
Publisher: MDPI AG
Date: 06-07-2020
Abstract: The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as erse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
Publisher: Oxford University Press (OUP)
Date: 16-05-2019
Abstract: The NRAO VLA Sky Survey (NVSS) rotation measure (RM) catalogue has enabled numerous studies in cosmic magnetism, and will continue being a unique data set complementing future polarization surveys. Robust comparisons with these new surveys will however require further understandings in the systematic effects present in the NVSS RM catalogue. In this paper, we make careful comparisons between our new on-axis broad-band observations with the Karl G. Jansky Very Large Array and the NVSS RM results for 23 sources. We found that two unpolarized sources were reported as polarized at about 0.5 per cent level in the RM catalogue, and noted significant differences between our newly derived RM values and the catalogue values for the remaining 21 sources. These discrepancies are attributed to off-axis instrumental polarization in the NVSS RM catalogue. By adopting the 0.5 per cent above as the typical off-axis instrumental polarization litude, we quantified its effect on the reported RMs with a simulation, and found that on average the RM uncertainties in the catalogue have to be increased by ${\\approx } 10\\, {{\\ \\rm per\\ cent}}$ to account for the off-axis instrumental polarization effect. This effect is more substantial for sources with lower fractional polarization, and is a function of the source’s true RM. Moreover, the distribution of the resulting RM uncertainty is highly non-Gaussian. With the extra RM uncertainty incorporated, we found that the RM values from the two observations for most (18 out of 21) of our polarized targets can be reconciled. The remaining three are interpreted as showing hints of time variabilities in RM.
Publisher: American Astronomical Society
Date: 25-07-2023
Abstract: Faraday rotation measures (RMs) have been used for many studies of cosmic magnetism, and in most cases having more RMs is beneficial for those studies. This has lead to the development of RM surveys that have produced large catalogs, as well as meta-catalogs collecting RMs from many different publications. However, it has been difficult to take full advantage of all of these RMs, as the in idual catalogs have been published in many different places, and in many different formats. In addition, the polarization spectra used to determine these RMs are rarely published, limiting the ability to reanalyze data as new methods or additional observations become available. We propose a standard convention for RM catalogs, RMTable2023, and a standard for source-integrated polarized spectra of radio sources, PolSpectra2023. These standards are intended to maximize the value and utility of these data for researchers and to make them easier to access. To demonstrate the use of the RMTable2023 standard, we have produced a consolidated catalog of 55,819 RMs collected from 42 published catalogs.
Publisher: EDP Sciences
Date: 08-2022
DOI: 10.1051/0004-6361/202142878
Abstract: 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 that are free from thermal contamination. Aims. We define a s le 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–star formation rate (SFR) relation using SFRs derived from total infrared and H α + 24-μm emission. Results. The radio–SFR relation at 144 MHz is clearly super-linear with L 144 MHz ∝ SFR 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 (CREs). However, the radio spectral index maps show 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 SFRs 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 that employs the galaxy mass as a proxy for the calorimetric efficiency.
Publisher: MDPI AG
Date: 24-11-2016
Publisher: Oxford University Press (OUP)
Date: 16-09-2016
Publisher: EDP Sciences
Date: 10-2023
Publisher: Oxford University Press (OUP)
Date: 09-02-2018
DOI: 10.1093/MNRAS/STY325
Publisher: EDP Sciences
Date: 02-2023
DOI: 10.1051/0004-6361/202346008
Abstract: Context. The existence of magnetic fields in the circumgalactic medium (CGM) is largely unconstrained. Their detection is important as magnetic fields can have a significant impact on the evolution of the CGM, and, in turn, the fields can serve as tracers for dynamical processes in the CGM. Aims. Using the Faraday rotation of polarised background sources, we aim to detect a possible excess of the rotation measure in the surrounding area of nearby galaxies. Methods. We used 2461 residual rotation measures (RRMs) observed with the LOw Frequency ARray (LOFAR), where the foreground contribution from the Milky Way is subtracted. The RRMs were then studied around a subset of 183 nearby galaxies that was selected by apparent B -band magnitude. Results. We find that, in general, the RRMs show no significant excess for small impact parameters (i.e., the perpendicular distance to the line of sight). However, if we only consider galaxies at higher inclination angles and sightlines that pass close to the minor axis of the galaxies, we find significant excess at impact parameters of less than 100 kpc. The excess in |RRM| is 3.7 rad m −2 with an uncertainty between ±0.9 rad m −2 and ±1.3 rad m −2 depending on the statistical properties of the background (2.8 σ –4.1 σ ). With electron densities of ∼10 −4 cm −3 , this suggests magnetic field strengths of a few tenths of a microgauss. Conclusions. Our results suggest a slow decrease in the magnetic field strength with distance from the galactic disc, as expected if the CGM is magnetised by galactic winds and outflows.
Publisher: MDPI AG
Date: 16-10-2017
Start Date: 2013
End Date: 12-2018
Amount: $315,000.00
Funder: Australian Research Council
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