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We present the HI distribution of galaxies from the Continuum Halos in Nearby Galaxies - an EVLA Survey (CHANG-ES). Though the observational mode was not optimized for detecting HI, we successfully produce HI cubes for 19 galaxies. The moment-0 maps from this work are available on CHANG-ES data release website, i.e., https://www.queensu.ca/changes. Our sample is dominated by star-forming, HI-rich galaxies at distances from 6.27 to 34.1 Mpc. HI interferometric images on two of these galaxies (NGC 5792 and UGC 10288) are presented here for the first time, while 12 of our remaining sample galaxies now have better HI spatial resolutions and/or sensitivities of intensity maps than those in existing publications. We characterize the average scale heights of the HI distributions for a subset of most inclined galaxies (inclination > 80 deg), and compare them to the radio continuum intensity scale heights, which have been derived in a similar way. The two types of scale heights are well correlated, with similar dependence on disk radial extension and star formation rate surface density but different dependence on mass surface density. This result indicates that the vertical distribution of the two components may be governed by similar fundamental physics but with subtle differences., 27 pages, 10 figures, accepted for publication in MNRAS

We present new radio continuum images of the edge-on starburst galaxy NGC 5775, from LOFAR (140 MHz) and the Karl G. Jansky Very Large Array CHANG-ES survey (1500 MHz). We trace the non-thermal radio halo up to 13 kpc from the disc, measuring the non-thermal spectral index and estimating the total equipartition magnetic field strength (≈13 μG in the disc and ≈7 μG above the plane). The radio halo has a similar extent at both frequencies, displays evidence for localized cosmic ray streaming coinciding with prominent H α filaments and vertical extensions of the regular magnetic field, and exhibits a boxy morphology especially at 140 MHz. In order to understand the nature of the disc–halo flow, we extend our previous model of cosmic ray propagation by implementing an iso-thermal wind with a tunable ‘flux tube’ (approximately hyperboloidal) geometry. This updated model is successful in matching the vertical distribution of non-thermal radio emission, and the vertical steepening of the associated spectral index, in a consistent conceptual framework with few free parameters. Our new model provides the opportunity to estimate the mass outflow driven by the star formation process, and we find an implied rate of M˙≈3–6M⊙yr−1 (≈40–80 per cent of the star formation rate) if the escape velocity is reached, with substantial uncertainty arising from the poorly understood distribution of interstellar medium material entrained in the vertical flow. The wind may play a role in influencing the vertical gradient in rotational velocity. © 2021 The Author(s)., This paper is based (in part) on data obtained with the International LOFAR Telescope (ILT) under project code LC1_046. LOFAR (van Haarlem et al. 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. GH thanks Phil Edwards for useful feedback after a critical reading of the manuscript, and Tim Galvin for advice and help with tricky plotting issues. We would like to thank B. P. Brian Yu, for kindly providing us with their computer code of the cosmic ray-driven wind model. We thank the anonymous referee for a comprehensive review and for comments that led to substantial improvements to the paper. MB acknowledges support from the Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy - EXC 2121 ‘Quantum Universe’ - 390833306. This research was undertaken as an activity organized by the LOFAR Magnetism Key Science Project (MKSP; https://lofar-mksp.org/)., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Context. The magnetic field in spiral galaxies is known to have a large-scale spiral structure along the galactic disk and is observed as X-shaped in the halo of some galaxies. While the disk field can be well explained by dynamo action, the three-dimensional structure of the halo field and its physical nature are still unclear. Aims. As first steps towards understanding the halo fields, we want to clarify whether or not the observed X-shaped field is a wide-spread pattern in the halos of spiral galaxies. We also aim to investigate whether these halo fields are simply turbulent fields ordered by compression or shear (anisotropic turbulent fields), or have a large-scale regular structure. Methods. Analysis of the Faraday rotation in the halo is used as a tool to distinguish anisotropic turbulent fields from large-scale magnetic fields. However, this has been challenging until recently because of the faint halo emission in linear polarization. Our sensitive VLA broadband observations in C-band and L-band of 35 spiral galaxies seen edge-on (called CHANG-ES) allowed us to perform rotation measure synthesis (RM synthesis) in their halos and to analyze the results. We further accomplished a stacking of the observed polarization maps of 28 CHANG-ES galaxies in C-band. Results. Though the stacked edge-on galaxies were of different Hubble type, and had differing star formation activity and interaction activity, the stacked image clearly reveals an X-shaped structure of the apparent magnetic field. We detected a large-scale (coherent) halo field in all 16 galaxies that have extended polarized emission in their halos. We detected large-scale field reversals in all of their halos. In six galaxies, these are along lines that are approximately perpendicular to the galactic midplane (vertical RMTL) with about 2 kpc separation. Only in NGC 3044 and possibly in NGC 3448 did we observe vertical giant magnetic ropes (GMR) similar to those detected recently in NGC 4631. Conclusions. The observed X-shaped structure of the halo field seems to be an underlying feature of spiral galaxies. It can be regarded as the two-dimensional projection of the regular magnetic field which we found to have scales of typically 1 kpc or larger observed over several kiloparsecs. The ordered magnetic field extends far out in the halo and beyond. We detected large-scale magnetic field reversals in the halo that may indicate that GMR are more or less tightly wound. With these discoveries, we hope to stimulate model simulations for the halo magnetic field that should also explain the determined asymmetry of the polarized intensity (PI). © M. Krause et al. 2020., The Dunlap Institute is funded through an endowment established by the David Dunlap family and the University of Toronto.

With 8 hours of observations, VERITAS confirms the detection of two very high energy gamma-ray sources. The gamma-ray binary LS 5039 is detected with a statistical significance of $8.8\sigma$. The measured flux above 1 TeV is $(2.5 \pm 0.4) \times 10^{-12} \rm \, cm^{-2} \, s^{-1}$ near inferior conjunction and $(7.8 \pm 2.8) \times 10^{-13} \rm \, cm^{-2} \, s^{-1}$ near superior conjunction. The pulsar wind nebula HESS J1825-137 is detected with a statistical significance of $6.7\sigma$ and a measured flux above 1 TeV of $(3.9 \pm 0.8) \times 10^{-12} \rm \, cm^{-2} \, s^{-1}$., Comment: 4 pages, 2 figures

NGC 4631 is an interacting galaxy that exhibits one of the largest, gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and cosmic-ray propagation properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99 GHz) in the C and D array configurations, and at L-band (1.57 GHz) in the B, C, and D array configurations. Complementary observations of NGC 4631 with the Effelsberg telescope were performed at 1.42 and 4.85 GHz. The interferometric total intensity data were combined with the single-dish Effelsberg data in order to recover the missing large-scale total power emission. The thermal and nonthermal components of the total radio emission were separated by estimating the thermal contribution through the extinction-corrected H$\alpha$ emission. The H$\alpha$ radiation was corrected for extinction using a linear combination of the observed H$\alpha$ and 24 $\mu$m data. NGC 4631 has a global thermal fraction at 5.99 (1.57) GHz of 14$\pm$3% (5.4$\pm$1.1%). The mean scale heights of the total emission in the radio halo (thick disk) at 5.99 (1.57) GHz are $1.79\pm0.54$ kpc ($1.75\pm0.27$ kpc) and have about the same values for the synchrotron emission. The total magnetic field of NGC 4631 has a mean strength of $\rm{\langle B_{eq}\rangle} \simeq 9 \rm{\mu G}$ in the disk, and a mean strength of $\rm{\langle B_{eq}\rangle}~\simeq 7~\rm{\mu G}$ in the halo. We also studied a double-lobed background radio galaxy southwest of NGC 4631, which is an FR~II radio galaxy according to the distribution of spectral index across the lobes. From the halo scale heights we estimated that the radio halo is escape-dominated with convective cosmic ray propagation, and conclude that there is a galactic wind in the halo of NGC 4631., Comment: 15 pages, 13 figures, accepted to be published in A&A

NGC 4631 is an interacting galaxy which exhibits one of the largest gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and polarization properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99 GHz) in the C & D array configurations, and at L-band (1.57 GHz) in the B, C, & D array configurations. The Rotation Measure Synthesis algorithm was utilized to derive the polarization properties. We detected linearly polarized emission at C-band and L-band. The magnetic field in the halo is characterized by strong vertical components above and below the central region of the galaxy. The magnetic field in the disk is only clearly seen in the eastern side of NGC 4631, where it is parallel to the plane of the major axis of the galaxy. We detected for the first time a large-scale, smooth Faraday depth pattern in a halo of an external spiral galaxy, which implies the existence of a regular (coherent) magnetic field. A quasi-periodic pattern in Faraday depth with field reversals was found in the northern halo of the galaxy. The field reversals in the northern halo of NGC 4631, together with the observed polarization angles, indicate giant magnetic ropes (GMRs) with alternating directions. To our knowledge, this is the first time such reversals are observed in an external galaxy., 8 pages, 7 figures, accepted to be published in A&A

We present radio continuum maps of 12 nearby ($D\leq 27~\rm Mpc$), edge-on ($i\geq 76^{\circ}$), late-type spiral galaxies mostly at $1.4$ and 5 GHz, observed with the Australia Telescope Compact Array, Very Large Array, Westerbork Synthesis Radio Telescope, Effelsberg 100-m and Parkes 64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detection in the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick disc that can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER (SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmic-ray transport models to the vertical model profiles of the non-thermal intensity and to the non-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (or diffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scale heights range from 2 to 8 kpc with an average across the sample of $3.0\pm 1.7~\rm kpc$; they show no correlation with either star-formation rate (SFR), SFR surface density ($\Sigma_{\rm SFR}$) or rotation speed ($V_{\rm rot}$). The advection speeds range from 100 to $700~\rm km\,s^{-1}$ and display correlations of $V\propto \rm SFR^{0.36\pm 0.06}$ and $V\propto \Sigma_{\rm SFR}^{0.39\pm 0.09}$; they agree remarkably well with the escape velocities ($0.5\leq V/V_{\rm esc}\leq 2$), which can be explained by cosmic-ray driven winds. Radio haloes show the presence of disc winds in galaxies with $\Sigma_{\rm SFR} > 10^{-3}~\rm M_{\odot}\,yr^{-1}\,kpc^{-2}$ that extend over several kpc and are driven by processes related to the distributed star formation in the disc., Comment: 39 pages, 20 colour figures, 10 tables. Accepted by MNRAS

The CHANG-ES galaxy sample consists of 35 nearby edge-on galaxies that have been observed using the VLA at 1.6 and 6.0 GHz. Here we present the third data release of our sample, namely, the B configuration 1.6 GHz sample. In addition, we make available the band-to-band spectral index maps between 1.6 and 6.0 GHz, the latter taken in the matching resolution C configuration. The images can be downloaded from https://www.queensu.ca/changes. These are our highest-resolution images (≈3″), and we examine the possible presence of low-luminosity active galactic nuclei (AGNs) in the sample, as well as some in-disk structure. New features can be seen in the spectral index maps that are masked in the total intensity emission, including hidden spiral arms in NGC 3448 and two previously unknown radio lobes on either side of the nucleus of NGC 3628. Our AGN detection rate, using only radio criteria, is 55%, which we take as a lower limit because some weaker embedded AGNs are likely present that could be revealed at higher resolution. Archival XMM-Newton data were used to search for further fingerprints of the AGNs in the studied sample. In galaxy disks, discrete regions of flat spectral index are seen, likely due to a thermal emission fraction that is higher than the global average.© 2019. The American Astronomical Society. All rights reserved., The first author would like to thank the Natural Sciences and Engineering Research Council of Canada for a Discovery Grant.

The CHANG-ES (Continuum Halos in Nearby Galaxies) survey of 35 nearby edge-on galaxies is revealing new and sometimes unexpected and startling results in their radio continuum emission. The observations were in wide bandwidths centred at 1.6 and 6.0 GHz. Unique to this survey is full polarization data showing magnetic field structures in unprecedented detail, resolution and sensitivity for such a large sample. A wide range of new results are reported here, some never before seen in any galaxy. We see circular polarization and variability in active galactic nuclei (AGNs), in-disk discrete features, disk-halo structures sometimes only seen in polarization, and broad-scale halos with reversing magnetic fields, among others. This paper summarizes some of the CHANG-ES results seen thus far., For the first author, this research was funded by the Natural Sciences and Engineering Research Council of Canada Discovery grant number 388-528, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

We analyze the magnetic field geometry and the transport processes of the cosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio continuum data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band). Supplementary X-ray data are used to investigate the hot gas in NGC 4666. We determine the radio scale heights of total power emission at both frequencies for this galaxy. We show the magnetic field orientations derived from the polarization data. Using rotation measure (RM) synthesis we further study the behavior of the RM values along the disk in C-band to investigate the large-scale magnetic-field pattern. We use the revised equipartition formula to calculate a map of the magnetic field strength. Furthermore, we model the processes of cosmic-ray transport into the halo with the 1D SPINNAKER model. The extended radio halo of NGC 4666 is box-shaped and is probably produced by the previously observed supernova-driven superwind. This is supported by our finding of an advective cosmic-ray transport such as that expected for a galactic wind. The scaleheight analysis revealed an asymmetric halo above and below the disk as well as between the two sides of the major axis. A central point source as well as a bubble structure is seen in the radio data for the first time. Our X-ray data show a box-shaped hot halo around NGC 4666 and furthermore confirm the AGN nature of the central source. NGC 4666 has a large-scale X-shaped magnetic field in the halo, as has been observed in other edge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666 shows hints of field reversals along its radius, which is the first detection of this phenomenon in an external galaxy., 23 pages, accepted for publication in A&A

We present new narrow-band H-alpha imaging for 24 nearby edge-on galaxies in the CHANG-ES survey. We use the images in conjunction with WISE 22 micron imaging of the sample to estimate improved star formation rates (SFRs) using the updated recipe from Vargas et al. (2018). We explore correlations between the updated star formation properties and radio continuum scale heights, scale lengths, and diameters, measured in Krause et al. (2018). We find a newly discovered correlation between SFR and radio scale height that did not exist using mid-IR only SFR calibrations. This implies that a mid-IR extinction correction should be applied to SFR calibrations when used in edge-on galaxies, due to attenuation by dust. The updated SFR values also show newly discovered correlations with radio scale length and radio diameter, implying that the previously-measured relationship between radio scale height and radio diameter originates from star formation within the disk. We also identify a region of star formation located at extreme distance from the disk of NGC 4157, possibly ionized by a single O5.5 V star. This region is spatially coincident with an XUV disk feature, as traced by GALEX NUV imaging. We theorize that the star formation feature arose due to gravitational instability within gas from an accretion event. New H-alpha images from this work can be found at the CHANG-ES data release web site, https://www.queensu.ca/changes., Comment: Accepted to ApJS, 38 pages, 32 figures

Using the Continuum HAloes in Nearby Galaxies - an EVLA Survey (CHANG-ES) radio continuum data from the Karl G. Jansky Very Large Array (VLA) in two frequency bands (C-band, L-band), we analyzed the radio properties, including polarization and the transport processes of the CR electrons (CREs), in the edge-on spiral galaxy NGC 4013. Supplementary LOw-Frequency ARray (LOFAR) data at 150MHz are used to study the low-frequency properties of this galaxy and X-ray (Chandra, XMM-Newton) data are used to investigate the central region. The central point source dominates the radio continuum in both CHANG-ES bands, but no clear AGN classification is possible at this time. The scale height analysis shows that Gaussian fits, with halo scale heights of 1.2 kpc in C-band, 2.0 kpc in L-band, and 3.1 kpc at 150 MHz, better represent the intensity profiles than do exponential fits. The radio continuum halo of NGC 4013 in C-band is rather small, while the low-frequency LOFAR data reveal a large halo. The polarization data reveal plane-parallel, regular magnetic fields within the entire disk and vertical halo components out to heights of about 6 kpc indicating the presence of an axisymmetric field having a radial component pointing outwards. The mean magnetic field strength of the disk of NGC 4013 of 6.6 $\mu$G (using the revised equipartition formula) is rather small. The interaction and the low star formation rate (SFR) across the disk of NGC 4013 probably influence the appearance of its radio continuum. Several observable quantities give consistent evidence that the CR transport in the halo of NGC 4013 is diffusive: the frequency dependence of the synchrotron scale height, the disk/halo flux density ratio, the vertical profile of the synchrotron spectral index, the small propagation speed measured modeled with spinnaker, and the low temperature of the X-ray emitting hot gas., Comment: 24 pages, 27 figures, accepted for publication in A&A

The Cherenkov Telescope Array (CTA) is the major next-generation observatory for ground-based very-high-energy gamma-ray astronomy. It will improve the sensitivity of current ground-based instruments by a factor of five to twenty, depending on the energy, greatly improving both their angular and energy resolutions over four decades in energy (from 20 GeV to 300 TeV). This achievement will be possible by using tens of imaging Cherenkov telescopes of three successive sizes. They will be arranged into two arrays, one per hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We present here the optimised and final telescope arrays for both CTA sites, as well as their foreseen performance, resulting from the analysis of three different large-scale Monte Carlo productions.© 2019, We gratefully acknowledge financial support from the following agencies and organizations: State Committee of Science of Armenia, Armenia; The Australian Research Council, Astronomy Australia Ltd, The University of Adelaide, Australian National University, Monash University, The University of New South Wales, The University of Sydney, Western Sydney University, Australia; Federal Ministry of Science, Research and Economy, and Innsbruck University, Austria; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ), Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), Ministry of Science, Technology, Innovations and Communications (MCTIC), Brasil; Ministry of Education and Science, National RI Roadmap Project D01-153/28.08.2018, Bulgaria; The Natural Sciences and Engineering Research Council of Canada and the Canadian Space Agency, Canada; CONICYT-Chile grants PFB-06, FB0821, ACT 1406, FONDECYT-Chile grants 3160153, 3150314, 1150411, 1161463, 1170171, Pontificia Universidad Catolica de Chile Vice-Rectory of Research internationalization grant under MINEDUC agreement PUC1566, Chile, Croatian Science Foundation, Rudjer Boskovic Institute, University of Osijek, University of Rijeka, University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Zagreb, Faculty of Electrical Engineering and Computing, Croatia; Ministry of Education, Youth and Sports, MEYS LM2015046, LTT17006 and EU/MEYS CZ.02.1.01/0.0/0.0/16_013/0001403, CZ.02.1.01/0.0/0.0/17_049/0008422, Czech Republic; Ministry of Higher Education and Research, CNRS-INSU and CNRS-IN2P3, CEA-Irfu, ANR, Regional Council Ile-de France, Labex ENIGMASS, OSUG2020, P210 and OCEVU, France; Max Planck Society, BMBF, DESY, Helmholtz Association, Germany; Department of Atomic Energy, Department of Science and Technology, India; Istituto Nazionale di Astrofisica (INAF), Istituto Nazionale di Fisica Nucleare (INFN), MIUR, Istituto Nazionale di Astrofisica (INAF-OABRERA) Grant Fondazione Cariplo/Regione Lombardia ID 2014-1980/RST_ERC, Italy; ICRR, University of Tokyo, JSPS, MEXT, Japan; Netherlands Research School for Astronomy (NOVA), Netherlands Organization for Scientific Research (NWO), Netherlands; University of Oslo, Norway; Ministry of Science and Higher Education, DIR/WK/2017/12, the National Centre for Research and Development and the National Science Centre, UMO-2016/22/M/ST9/00583, Poland; Slovenian Research Agency, Slovenia, grants P1-0031, P1-0385, 10-0033, J1-9146; South African Department of Science and Technology and National Research Foundation through the South African Gamma-Ray Astronomy Programme, South Africa; MINECO National R+D+I, Severo Ochoa, Maria de Maeztu, CDTI, PAIDI, UJA, FPA2017-90566-REDC, Spain; Swedish Research Council, Royal Physiographic Society of Lund, Royal Swedish Academy of Sciences, The Swedish National Infrastructure for Computing (SNIC) at Lunarc (Lund), Sweden; Swiss National Science Foundation (SNSF), Ernest Boninchi Foundation, Switzerland; Durham University, Leverhulme Trust, Liverpool University, University of Leicester, University of Oxford, Royal Society, Science and Technology Facilities Council, UK; U.S. National Science Foundation, U.S.Department of Energy, Argonne National Laboratory, Barnard College, University of California, University of Chicago, Columbia University, Georgia Institute of Technology, Institute for Nuclear and Particle Astrophysics (INPAC-MRPI program), Iowa State University, the Smithsonian Institution, Washington University McDonnell Center for the Space Sciences, The University of Wisconsin and the Wisconsin Alumni Research Foundation, USA. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreements no 262053 and no 317446. This project is receiving funding from the European Union's Horizon 2020 research and innovation programs under agreement no 676134.

Cosmic-ray electrons (CREs) originating from the star-forming discs of spiral galaxies frequently form extended radio haloes that are best observable in edge-on galaxies. For the present study we selected two nearby edge-on galaxies from the CHANG-ES survey, NGC 891 and 4565, which differ largely in halo size and SFR. To figure out how such differences are related to the CRE transport in disc and halo, we use wide-band 1.5 and 6 GHz VLA observations obtained in the B, C, and D configurations, and combine the 6 GHz images with Effelsberg observations to correct for missing short spacings. We study the spatially resolved non-thermal spectral index distribution in terms of CRE spectral ageing, compute total magnetic field strengths assuming energy equipartition between CRs and magnetic fields, and also determine synchrotron scale heights. Based on the vertical profiles of synchrotron intensity and spectral index, we create purely advective and purely diffusive CRE transport models by numerically solving the 1D diffusion-loss equation. In particular, we investigate for the first time the radial dependence of synchrotron and magnetic field scale heights, advection speeds and diffusion coefficients in these two galaxies. We find the spectral index distribution of NGC 891 to be mostly consistent with continuous CRE injection, while in NGC 4565 the local synchrotron spectra are more in line with discrete-epoch CRE injection (JP or KP models). This implies that CRE injection timescales are lower than the synchrotron cooling timescales. The scale height of NGC 891 increases with radius, indicating that synchrotron losses are significant. NGC 891 is probably dominated by advective CRE transport at a velocity of $\gtrsim150\,\mathrm{km\,s^{-1}}$. In contrast, NGC 4565 is diffusion-dominated up to $z=1$ kpc or higher, with a diffusion coefficient of $\geq2\times10^{28}\,\mathrm{cm^2\,s^{-1}}$., Comment: 37 pages, 22 figures, accepted for publication in A&A

We present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. We find that for exponential halo magnetic field distributions advection leads to approximately exponential radio continuum intensity profiles, whereas diffusion leads to profiles that can be better approximated by a Gaussian function. Accordingly, the vertical radio spectral profiles for advection are approximately linear, whereas for diffusion they are of `parabolic' shape. We compare our models with deep ATCA observations of two edge-on galaxies, NGC 7090 and 7462, at $\lambda\lambda$ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with $V=150^{+80}_{-30}~\rm km\,s^{-1}$, and that the one in NGC 7462 is diffusion dominated with $D=3.0\pm 1.0 \times 10^{28}E_{\rm GeV}^{0.5}~\rm cm^2\,s^{-1}$. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of $h_{\rm B1}=0.8\pm 0.1$ kpc and $h_{\rm B2}=4.7\pm 1.0$ kpc. NGC 7462 has only a thick radio disc with $h_{\rm B2}=3.8\pm 1.0$ kpc. In both galaxies, the magnetic field scale heights are significantly smaller than what estimates from energy equipartition would suggest. A non-negligible fraction of cosmic ray electrons can escape from NGC 7090, so that this galaxy is not an electron calorimeter., Comment: MNRAS accepted. 19 pages, 10 figures, 5 tables plus 4 pages of appendix

Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by VLBA at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed., Comment: Accepted for publication in the Astrophysical Journal

Low-frequency radio continuum observations of edge-on galaxies are ideal to study cosmic-ray electrons (CREs) in halos via radio synchrotron emission and to measure magnetic field strengths. We obtained new observations of the edge-on spiral galaxy NGC 891 at 129-163 MHz with the LOw Frequency ARray (LOFAR) and at 13-18 GHz with the Arcminute Microkelvin Imager (AMI) and combine them with recent high-resolution Very Large Array (VLA) observations at 1-2 GHz, enabling us to study the radio continuum emission over two orders of magnitude in frequency. The spectrum of the integrated nonthermal flux density can be fitted by a power law with a spectral steepening towards higher frequencies or by a curved polynomial. Spectral flattening at low frequencies due to free-free absorption is detected in star-forming regions of the disk. The mean magnetic field strength in the halo is 7 +- 2 $\mu$G. The scale heights of the nonthermal halo emission at 146 MHz are larger than those at 1.5 GHz everywhere, with a mean ratio of 1.7 +- 0.3, indicating that spectral ageing of CREs is important and that diffusive propagation dominates. The halo scale heights at 146 MHz decrease with increasing magnetic field strengths which is a signature of dominating synchrotron losses of CREs. On the other hand, the spectral index between 146 MHz and 1.5 GHz linearly steepens from the disk to the halo, indicating that advection rather than diffusion is the dominating CRE transport process. This issue calls for refined modelling of CRE propagation., Comment: Accepted for publication in Astronomy & Astrophysics

We detect 5 galaxies in the CHANG-ES (Continuum Halos in Nearby Galaxies -- an EVLA Survey) sample that show circular polarization (CP) at L-band in our high resolution data sets. Two of the galaxies (NGC~4388 and NGC~4845) show strong Stokes $V/I\,\equiv\,m_C\,\sim\,2$\%, two (NGC~660 and NGC~3628) have values of $m_C\sim \,0.3$\%, and NGC~3079 is a marginal detection at $m_C\sim \,0.2$\%. The two strongest $m_C$ galaxies also have the most luminous X-ray cores and the strongest internal absorption in X-rays. We have expanded on our previous Faraday conversion interpretation and analysis and provide analytical expressions for the expected $V$ signal for a general case in which the cosmic ray electron energy spectral index can take on any value. We provide examples as to how such expressions could be used to estimate magnetic field strengths and the lower energy cutoff for CR electrons. Four out of our detections are {\it resolved}, showing unique structures, including a {\it jet} in NGC~4388 and a CP `conversion disk' in NGC~4845. The conversion disk is inclined to the galactic disk but is perpendicular to a possible outflow direction. Such CP structures have never before been seen in any galaxy to our knowledge. None of the galaxy cores show linear polarization at L-band. Thus CP may provide a unique probe of physical conditions deep into radio AGNs., Comment: 30 pages, 4 figures, accepted to MNRAS

Context. The composition and morphology of the interstellar medium in starburst galaxies has been well investigated, but the magnetic field properties are still uncertain. The nearby starburst galaxy M 82 provides a unique opportunity to investigate the mechanisms leading to the amplification and reduction of turbulent and regular magnetic fields. Aims. An investigation of the magnetic field properties in M 82 will give insight into mechanisms to generate and maintain a magnetic field as well as depolarisation mechanisms. Possible scenarios of the contribution of the magnetic field to the star-formation rate are evaluated. Methods. Archival data from the Very Large Array (VLA) were combined and re-reduced to cover the wavelength regime at λ 3 cm and λ 6 cm. Complementary data from the Westerbork Synthesis Radio Telescope (WSRT) at λ 18 cm and λ 22 cm were reduced and analysed using the RM-Synthesis technique. Results. All observations revealed polarised emission in the inner part of the galaxy, while extended polarised emission up to a distance of 2 kpc from the disk was only detected at λ 18 cm and λ 22 cm. The observations hint at a magnetised bar in the inner part of the galaxy. We calculate the mass inflow rate due to magnetic stress of the bar to 7.1 M ⊙ yr -1 , which can be a significant contribution to the star-formation rate (SFR) of M 82 of ~ 13 M ⊙ yr -1 . The halo shows polarised emission, which might be the remnant of a regular disk field. Indications for a helical field in the inner part of the outflow cone are provided. The coherence length of the magnetic field in the centre could be estimated to 50 pc, which is similar to the size of giant molecular clouds. Using polarisation spectra more evidence for a close coupling of the ionised gas and the magnetic field as well as a two-phase magnetic field topology were found. Electron densities in the halo (⟨ n e ⟩ ≈ 0.009 cm -3 ) are similar to the ones found in the Milky Way. Conclusions. The magnetic field morphology is similar to the one in other nearby starburst galaxies (NGC 1569, NGC 253) with possible large-scale magnetic loops in the halo and a helical magnetic field inside the outflow cones. The special combination of a magnetic bar and a circumnuclear ring are able to significantly raise the star-formation rate in this galaxy by magnetic braking, but cannot be the cause for all starbursts.

We present constraints on the annihilation cross section of WIMP dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of $\sim$230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is $1.35\times 10^{-23} {\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the bottom quark ($b\bar{b}$) final state, $2.85\times 10^{-24}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the tau lepton ($\tau^{+}\tau^{-}$) final state and $1.32\times 10^{-25}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the gauge boson ($\gamma\gamma$) final state., Comment: 14 pages, 9 figures, published in PRD, Ascii tables containing annihilation cross sections limits are available for download as ancillary files with readme.txt file description of limits

The astrophysical journal 836(1), 23 (2017). doi:10.3847/1538-4357/836/1/23, High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho's SNR is a particularly good target because it is a young, type Ia SNR that has been well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho's SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho's SNR with 147 hr of VERITAS and 84 months of Fermi-LAT observations, which represent about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92 ± 0.42$_{stat}$ ± 0.20$_{sys}$. It is also softer than the spectral index in the GeV energy range, 2.14 ± 0.09$_{stat}$ ± 0.02$_{sys}$, measured in this study using Fermi-LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi-LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously., Published by IOP Publ., Chicago, Ill. [u.a.]

Computing polarised intensities from noisy data in Stokes U and Q suffers from a positive bias that should be suppressed. To develop a correction method that, when applied to maps, should provide a distribution of polarised intensity that closely follows the signal from the source. We propose a new method to suppress the bias by estimating the polarisation angle of the source signal in a noisy environment with help of a modified median filter. We then determine the polarised intensity, including the noise, by projection of the observed values of Stokes U and Q onto the direction of this polarisation angle. We show that our new method represents the true signal very well. If the noise distribution in the maps of U and Q is Gaussian, then in the corrected map of polarised intensity it is also Gaussian. Smoothing to larger Gaussian beamsizes, to improve the signal-to-noise ratio, can be done directly with our method in the map of the polarised intensity. Our method also works in case of non-Gaussian noise distributions. The maps of the corrected polarised intensities and polarisation angles are reliable even in regions with weak signals and provide integrated flux densities and degrees of polarisation without the cumulative effect of the bias, which especially affects faint sources. Features at low intensity levels like 'depolarisation canals' are smoother than in the maps using the previous methods, which has broader implications, for example on the interpretation of interstellar turbulence., accepted for publication in Astronomy & Astrophysics

[Abridged] The Lupus I cloud is found between the Upper-Scorpius and the Upper-Centaurus-Lupus sub-groups, where the expanding USco HI shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL. We investigate if the Lupus I molecular could have formed in a colliding flow, and how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. We performed APEX 13CO and C18O observations of three parts of Lupus. We compare these results to the atomic hydrogen data from the GASS HI survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. We present evidence that the molecular gas of Lupus I is tightly linked to the atomic material of the USco shell. The CO emission in Lupus I is found mainly at velocities in the same range as the HI velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic Hi shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The non-thermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario where Lupus I is located in the interaction zone between the USco shell and the UCL wind bubble. The kinematics observations are consistent with a scenario where the Lupus I cloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counter-pressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation., Accepted for publication by A&A

We report on C-band (5 - 7 GHz) observations of the galaxy, NGC~2992, from the CHANG-ES sample. This galaxy displays an embedded nuclear double-lobed radio morphology within its spiral disk, as revealed in linearly polarized emission but {\it not} in total intensity emission. The radio lobes are kpc-sized, similar to what has been observed in the past for other Seyfert galaxies, and show ordered magnetic fields. NGC~2992 has shown previous evidence for AGN-related activity, but not the linearly polarized radio features that we present here. We draw attention to this galaxy as the first clear example (and prototype) of bipolar radio outflow that is revealed in linearly polarized emission only. Such polarization observations, which are unobscured by dust, provide a new tool for uncovering hidden weak AGN activity which may otherwise be masked by brighter unpolarized emission within which it is embedded. The radio lobes observed in NGC~2992 are interacting with the surrounding interstellar medium and offer new opportunities to investigate the interactions between nuclear outflows and the ISM in nearby galaxies. We also compare the radio emission with a new CHANDRA X-ray image of this galaxy. A new CHANG-ES image of NGC~3079 is also briefly shown as another example as to how much more obvious radio lobes appear in linear polarization as opposed to total intensity., 23 pages, 8 figures, accepted by MNRAS

How a galaxy regulates its SNe energy into different interstellar/circumgalactic medium components strongly affects galaxy evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz) continuum observations, we perform statistical analysis comparing multi-wavelength properties of the CHANG-ES galaxies. The high-quality JVLA data and edge-on orientation enable us for the first time to include the halo into the energy budget for a complete radio-flux-limited sample. We find tight correlations of $L_{\rm radio}$ with the mid-IR-based SFR. The normalization of our $I_{\rm 1.6GHz}/{\rm W~Hz^{-1}}-{\rm SFR}$ relation is $\sim$2-3 times of those obtained for face-on galaxies, probably a result of enhanced IR extinction at high inclination. We also find tight correlations between $L_{\rm radio}$ and the SNe energy injection rate $\dot{E}_{\rm SN(Ia+CC)}$, indicating the energy loss via synchrotron radio continuum accounts for $\sim0.1\%$ of $\dot{E}_{\rm SN}$, comparable to the energy contained in CR electrons. The integrated C-to-L-band spectral index is $\alpha\sim0.5-1.1$ for non-AGN galaxies, indicating a dominance by the diffuse synchrotron component. The low-scatter $L_{\rm radio}-{\rm SFR}$/$L_{\rm radio}-\dot{E}_{\rm SN (Ia+CC)}$ relationships have super-linear logarithmic slopes at $\sim2~\sigma$ in L-band ($1.132\pm0.067$/$1.175\pm0.102$) while consistent with linear in C-band ($1.057\pm0.075$/$1.100\pm0.123$). The super-linearity could be naturally reproduced with non-calorimeter models for galaxy disks. Using Chandra halo X-ray measurements, we find sub-linear $L_{\rm X}-L_{\rm radio}$ relations. These results indicate that the observed radio halo of a starburst galaxy is close to electron calorimeter, and a galaxy with higher SFR tends to distribute an increased fraction of SNe energy into radio emission (than X-ray)., Comment: 16 pages, 6 figures, 1 table, MNRAS in press

We obtained Spitzer/IRAC 3.6-8 micron images of the nearby spiral galaxy NGC 4258 to study possible interactions between dust and the radio jet. In our analysis we also included high-resolution radio continuum, H-alpha, CO, and X-ray data. Our data reveal that the 8 micron emission, believed to originate largely from PAH molecules and hot dust, is an excellent tracer of the normal spiral structure in NGC 4258, and hence it originates from the galactic plane. We investigated the possibility of dust destruction by the radio jet by calculating correlation coefficients between the 8 micron and radio continuum emissions along the jet in two independent ways, namely (i) from wavelet-transformed maps of the original images at different spatial scales, and (ii) from one-dimensional intensity cuts perpendicular to the projected path of the radio jet on the sky. No definitive sign of a correlation (or anticorrelation) was detected on relevant spatial scales with either approach, implying that any dust destruction must take place at spatial scales that are not resolved by our observations., Accepted for publication in the Astronomical Journal (11 pages, 10 figures, 1 table)

The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands. The sample average value for the radio scale heights of the halo are 1.1 +/- 0.3kpc in C-band and 1.4 +/- 0.7kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, the normalized scale height shows a tight anticorrelation with the mass surface density. The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk., accepted for publication in Astronomy & Astrophysics

We present integrated polarization properties of nearby spiral galaxies at 4.8 GHz, and models for the integrated polarization of spiral galaxy disks as a function of inclination. Spiral galaxies in our sample have observed integrated fractional polarization in the range < 1% to 17.6%. At inclinations less than 50 degrees, the fractional polarization depends mostly on the ratio of random to regular magnetic field strength. At higher inclinations, Faraday depolarization associated with the regular magnetic field becomes more important. The observed degree of polarization is lower ( 2 x 10^{21} W/Hz. The polarization angle of the integrated emission is aligned with the apparent minor axis of the disk for galaxies without a bar. In our axially symmetric models, the polarization angle of the integrated emission is independent of wavelength. Simulated distributions of fractional polarization for randomly oriented spiral galaxies at 4.8 GHz and 1.4 GHz are presented. We conclude that polarization measurements, e.g. with the SKA, of unresolved spiral galaxies allow statistical studies of the magnetic field in disk galaxies using large samples in the local universe and at high redshift. As these galaxies behave as idealized background sources without internal Faraday rotation, they can be used to detect large-scale magnetic fields in the intergalactic medium., 13 pages, 6 figures; Accepted for publication in The Astrophysical Journal

Aims. We investigate the cosmological evolution of large- and small-scale magnetic fields in galaxies in the light of present models of formation and evolution of galaxies. Methods. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled with galaxy formation and evolution. Results. The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few muG strength within a few 10^8 yr. This turbulent field served as a seed to the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z~10 and regular fields of muG strength and a few kpc coherence length were generated within 2 Gyr (at z~3), but field-ordering on the coherence scale of the galaxy size required an additional 6 Gyr (at z~0.5). Giant galaxies formed their disks at z~10, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at z~4. However, the age of the Universe is short for fully coherent fields in giant galaxies larger than 15 kpc to have been achieved. Dwarf galaxies should have hosted fully coherent fields at z~1. After a major merger, the strength of the turbulent field is enhanced by a factor of a few. Conclusions. This evolutionary scenario can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned SKA. We predict an anticorrelation between galaxy size and ratio between ordering scale and galaxy size (abridged)., Comment: 13 pages, 3 figures, accepted for publication to A&A; new version which incorporates suggestions of a language editor

We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright unresolved core with a surrounding weak central disk (1.8 kpc diameter). The core is variable over the 6 month time scale of the CHANG-ES data and has increased by a factor of $\approx$ 6 since 1995. The wide bandwidths of CHANG-ES have allowed us to determine the spectral evolution of this core which peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We show that the spectral turnover is dominated by synchrotron self-absorption and that the spectral evolution can be explained by adiabatic expansion (outflow), likely in the form of a jet or cone. The CHANG-ES observations serendipitously overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter (2013) which they interpret as due to a tidal disruption event (TDE) of a super-Jupiter mass object around a $10^5\, M_\odot$ black hole. We outline a standard jet model, provide an explanation for the observed circular polarization, and quantitatively suggest a link between the peak radio and peak X-ray emission via inverse Compton upscattering of the photons emitted by the relativistic electrons. We predict that it should be possible to resolve a young radio jet via VLBI as a result of this nearby TDE., 45 pages, 10 figures, accepted July 2, 2015 to the Astrophysical Journal

In this chapter, we highlight a number of science investigations that are enabled by the inclusion of Band 5 (4.6-13.8 GHz) for SKA1-MID science operations, while focusing on the astrophysics of star formation over cosmic time. For studying the detailed astrophysics of star formation at highredshift, surveys at frequencies ≳10 GHz have the distinct advantage over traditional ~1.4 GHz surveys as they are able to yield higher angular resolution imaging while probing higher rest frame frequencies of galaxies with increasing redshift, where emission of star-forming galaxies becomes dominated by thermal (free-free) radiation. In doing so, surveys carried out at ≳10 GHz provide a robust, dust-unbiased measurement of the massive star formation rate by being highly sensitive to the number of ionizing photons that are produced. To access this powerful star formation rate diagnostic requires that Band 5 be available for SKA1-MID. We additionally present a detailed science case for frequency coverage extending up to 30 GHz during full SKA2 operations, as this allows for highly diverse science while additionally providing contiguous frequency coverage between the SKA and ALMA, which will likely be the two most powerful interferometers for the coming decades. To enable this synergy, it is crucial that the dish design of the SKA be flexible enough to include the possibility of being fit with receivers operating up to 30 GHz.

Magnetic fields are an important ingredient of the interstellar medium (ISM). Besides their importance for star formation, they govern the transport of cosmic rays, relevant to the launch and regulation of galactic outflows and winds, which in turn are pivotal in shaping the structure of halo magnetic fields. Mapping the small-scale structure of interstellar magnetic fields in many nearby galaxies is crucial to understand the interaction between gas and magnetic fields, in particular how gas flows are affected. Elucidation of the magnetic role in, e.g., triggering star formation, forming and stabilising spiral arms, driving outflows, gas heating by reconnection and magnetising the intergalactic medium has the potential to revolutionise our physical picture of the ISM and galaxy evolution in general. Radio polarisation observations in the very nearest galaxies at high frequencies (>= 3 GHz) and with high spatial resolution (, 18 pages, 3 figures; to appear as part of 'Cosmic Magnetism' in Proceedings 'Advancing Astrophysics with the SKA' (AASKA14) as article PoS(AASKA14)094

Magnetic fields play an important role in shaping the structure and evolution of the interstellar medium (ISM) of galaxies, but the details of this relationship remain unclear. With SKA1, the 3D structure of galactic magnetic fields and its connection to star formation will be revealed. A highly sensitive probe of the internal structure of the magnetoionized ISM is the partial depolarization of synchrotron radiation from inside the volume. Different configurations of magnetic field and ionized gas within the resolution element of the telescope lead to frequency-dependent changes in the observed degree of polarization. The results of spectro-polarimetric observations are tied to physical structure in the ISM through comparison with detailed modeling, supplemented with the use of new analysis techniques that are being actively developed and studied within the community such as Rotation Measure Synthesis. The SKA will enable this field to come into its own and begin the study of the detailed structure of the magnetized ISM in a sample of nearby galaxies, thanks to its extraordinary wideband capabilities coupled with the combination of excellent surface brightness sensitivity and angular resolution., Comment: 11 pages, 1 figure; to appear as part of 'Cosmic Magnetism' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)106

We present the first part of the observations made for the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES project is to study and characterize the nature of radio halos, their prevalence as well as their magnetic fields, and the cosmic rays illuminating these fields. This paper reports observations with the compact D configuration of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the VLA, an unprecedented sensitivity was achieved for all polarization products. The beam resolution is an average of 9.6" and 36" with noise levels reaching approximately 6 and 30 microJy per beam for C- and L-bands, respectively (robust weighting). We present intensity maps in these two frequency bands (C and L), with different weightings, as well as spectral index maps, polarization maps, and new measurements of star formation rates (SFRs). The data products described herein are available to the public in the CHANG-ES data release available at www.queensu.ca/changes. We also present evidence of a trend among galaxies with larger halos having higher SFR surface density, and we show, for the first time, a radio continuum image of the median galaxy, taking advantage of the collective signal-to-noise ratio of 30 of our galaxies. This image shows clearly that a typical spiral galaxy is surrounded by a halo of magnetic fields and cosmic rays., Comment: 70 pages, of which 35 pages present the data of each galaxy

After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest to understand the accretion-ejection connections. These can, however, only be probed through simultaneous observations at several wavelengths. We made use of the INTEGRAL instruments to obtain long, almost uninterrupted observations from 2015 June 20$^{\mathrm{th}}$, 15:50 UTC to June 25$^{\mathrm{th}}$, 4:05 UTC, from the optical V-band, up to the soft $\gamma$-rays. V404 Cyg was extremely variable in all bands, with the detection of 18 flares with fluxes exceeding 6 Crab (20--40 keV) within 3 days. The flare recurrence can be as short as $\sim$ 20~min from peak to peak. A model-independent analysis shows that the $>$6 Crab flares have a hard spectrum. A simple 10--400 keV spectral analysis of the off-flare and flare periods shows that the variation in intensity is likely to be due to variations of a cut-off power law component only. The optical flares seem to be at least of two different types: one occurring in simultaneity with the X-ray flares, the other showing a delay greater than 10 min. The former could be associated with X-ray reprocessing by either an accretion disk or the companion star. We suggest that the latter are associated with plasma ejections that have also been seen in radio., Comment: 7 pages, 4 figures; accepted for publication in A&A as a letter

In order to analyze the importance of the star formation rate in generating and amplifying magnetic fields in the interstellar medium we obtained deep total power and polarization maps at 4.85 GHz of three late type spiral galaxies NGC4236, NGC4656 and IC2574 using the 100-m Effelsberg radio telescope. This was accompanied by imaging in the Halpha line. We also observed these objects at 1.4 GHz to obtain their integrated fluxes at this frequency and to determine their radio spectra. All galaxies were found to possess weak but detectable total power emission at 4.85 GHz, coincident with regions of recent star formation as traced by bright Halpha regions. The surface brightness of the radio-strongest object of our sample (NGC4656) is comparable to the radio-weakest objects in a sample of more than 50 normally star-forming spiral galaxies for which measurements at 4.8 GHz with the Effelsberg radio telescope are available. The fractional polarization of the 2 galaxies of our sample is less than 2%, significantly lower than for spiral galaxies of intermediate types, suggesting that the magnetic fields are not only weaker, but also less ordered than in spiral galaxies. The radio spectra of galaxies in our small sample are indicative of a substantial fraction of thermal emission, with a higher thermal fraction than in spirals with high star formation rates (SFR), while the nonthermal emission in our sample is relatively weak compared to spiral galaxies. We propose an equipartition model where the nonthermal emission increases ~SFR^(~1.4) and the ratio of nonthermal to thermal emission increases ~SFR^(~0.4). The objects of our sample still follow the radio-FIR correlation of surface brightness of the total emission, extending it towards the lowest values measured so far., Comment: 10 pages, 11 figures, accepted for publication in A&A

The venerable NOD2 data reduction software package for single-dish radio continuum observations, developed for use at the 100-m Effelsberg radio telescope, has been successfully applied over many decades. Modern computing facilities call for a new design. We aim to develop an interactive software tool with a graphical user interface (GUI) for the reduction of single-dish radio continuum maps. Special effort is given on the reduction of distortions along the scanning direction (scanning effects) by combining maps scanned in orthogonal directions or dual- or multiple-horn observations that need to be processed in a restoration procedure. The package should also process polarisation data and offer the possibility to include special tasks written by the individual user. Based on the ideas of the NOD2 package we developed NOD3, which includes all necessary tasks from the raw maps to the final maps in total intensity and linear polarisation. Furthermore, plot routines and several methods for map analysis are available. The NOD3 package is written in Python which allows to extend the package by additional tasks. The required data format for the input maps is FITS. NOD3 is a sophisticated tool to process and analyse maps from single-dish observations that are affected by 'scanning effects' due to clouds, receiver instabilities, or radio-frequency interference (RFI). The 'basket-weaving' tool combines orthogonally scanned maps to a final map that is almost free of scanning effects. The new restoration tool for dual-beam observations reduces the noise by a factor of about two compared to the NOD2 version. Combining single-dish with interferometer data in the map plane ensures the full recovery of the total flux density., 8 pages, 10 figures, Accepted for publication in A&A

Tidal disruption events (TDEs) occur when a star or sub-stellar object passes close enough to a galaxy's supermassive black hole to be disrupted by tidal forces. NGC 4845 (d=17 Mpc) was host to a TDE, IGR J12580+0134, detected in November 2010. Its proximity offers us a unique close-up of the TDE and its aftermath. We discuss new Very Long Baseline Array (VLBA) and Karl G. Jansky Very Large Array (JVLA) observations, which show that the radio flux from the active nucleus created by the TDE has decayed in a manner consistent with predictions from a jet-circumnuclear medium interaction model. This model explains the source's broadband spectral evolution, which shows a spectral peak that has moved from the submm (at the end of 2010) to GHz radio frequencies (in 2011-2013) to, 12 pages, 8 figures, ApJ, in press; v2 includes error corrections and slight additions to the analysis

Context. Despite numerous and detailed studies of the jets of active galactic nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most prominent unsolved problems, as is the launching mechanism of jets in AGN. The quasar 1308+326 (z = 0.997) allows us to study the overall properties of its jet in detail and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the Monitoring Of Jets in Active galactic nuclei with Very Long Baseline Array (VLBA) experiments (MOJAVE) survey permit us to trace out the structural changes in 1308+326 that we present here. The long-lived jet features in this source can be followed for about two decades.Aims. We investigate the very long baseline interferomety (VLBI) morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process.Methods. Fifty VLBA observations performed at 15 GHz from the MOJAVE survey were re-modeled with Gaussian components and re-analyzed (the time covered: 20 Jan. 1995–25 Jan. 2014). The analysis was supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5 GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle.Results. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position-angle (EVPA) rotation, we conclude that the jet of 1308+326 has a helical structure, meaning that the components are moving along helical trajectories and the trajectories themselves are also experiencing a precessing motion. A model of a precessing nozzle was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data till 2012 are consistent with a swing period of 16.9 yr. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, which is disturbed by the tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet.Conclusions. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet that is pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound-up filamentary structures are found. They are all related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a “component” comprises plasma tracing the magnetic field, which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation.

This 3rd paper in the CHANG-ES series shows the first results from our regular data taken with the Karl G. Jansky Very Large Array (JVLA). The edge-on galaxy, UGC 10288, has been observed in the B, C, and D configurations at L-band (1.5 GHz) and in the C and D configurations at C-band (6 GHz) in all polarization products. We show the first spatially resolved images in these bands,the first polarization images, and the first composed image at an intermediate frequency (4.1 GHz) which has been formed from a combination of all data sets. A surprising new result is the presence of a strong, polarized, double-lobed extragalactic radio source ({\it CHANG-ES A}) almost immediately behind the galaxy and perpendicular to its disk. The core of {\it CHANG-ES A} has an optical counterpart at a photometric redshift of $z_{phot}\,=\,0.39$; the southern radio lobe is behind the disk of UGC 10288 and the northern lobe is behind the halo region. This background `probe' has allowed us to do a preliminary Faraday Rotation analysis of the foreground galaxy, putting limits on the regular magnetic field and electron density in the halo of UGC 10288 in regions in which there is no direct detection of a radio continuum halo. We have revised the flux densities of the two sources individually as well as the star formation rate (SFR) for UGC 10288. UGC 10288 would have fallen well below the CHANG-ES flux density cutoff, had it been considered without the brighter contribution of the background source. UGC 10288 shows discrete high-latitude radio continuum features, but it does not have a {\it global} radio continuum halo. The total minimum magnetic field strength at a sample position in the arc is $\sim$ 10 $\mu$G. Thus, this galaxy still appears to be able to form substantial high latitude, localized features in spite of its relatively low SFR., Comment: 34 pages 11 figures Astronomical Journal, on-line publication date of Nov. 14, 2013

Context. Observations of polarized radio emission show that large-scale (regular) magnetic fields in spiral galaxies are not axisymmetric, but generally stronger in interarm regions. In some nearby galaxies such as NGC 6946 they are organized in narrow magnetic arms situated between the material spiral arms. Aims. The phenomenon of magnetic arms and their relation to the optical spiral arms (the material arms) call for an explanation in the framework of galactic dynamo theory. Several possibilities have been suggested but are not completely satisfactory; here we attempt a consistent investigation. Methods. We use a 2D mean-field dynamo model in the no-z approximation and add injections of small-scale magnetic field, taken to result from supernova explosions, to represent the effects of dynamo action on smaller scales. This injection of small scale field is situated along the spiral arms, where star-formation mostly occurs. Results. A straightforward explanation of magnetic arms as a result of modulation of the dynamo mechanism by material arms struggles to produce pronounced magnetic arms, at least with realistic parameters, without introducing new effects such as a time lag between Coriolis force and {\alpha}-effect. In contrast, by taking into account explicitly the small-scale magnetic field that is injected into the arms by the action of the star forming regions that are concentrated there, we can obtain dynamo models with magnetic structures of various forms that can be compared with magnetic arms. (abbrev). Conclusions. We conclude that magnetic arms can be considered as coherent magnetic structures generated by large-scale dynamo action, and associated with spatially modulated small-scale magnetic fluctuations, caused by enhanced star formation rates within the material arms., Comment: 13 pages, 8 figures, accepted for publication to A&A

We introduce a new survey to map the radio continuum halos of a sample of 35 edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of array configurations (B, C, and D) in order to compile the most comprehensive data set yet obtained for the study of radio halo properties. This is the first survey of radio halos to include all polarization products. In this first paper, we outline the scientific motivation of the survey, the specific science goals, and the expected improvements in noise levels and spatial coverage from the survey. Our goals include investigating the physical conditions and origin of halos, characterizing cosmic ray transport and wind speed, measuring Faraday rotation and mapping the magnetic field, probing the in-disk and extraplanar far-infrared - radio continuum relation, and reconciling non-thermal radio emission with high-energy gamma-ray models. The sample size allows us to search for correlations between radio halos and other properties, including environment, star formation rate, and the presence of AGNs. In a companion paper (Paper II) we outline the data reduction steps and present the first results of the survey for the galaxy, NGC 4631., Comment: 17 pages, 1 figure, accepted to the Astronomical Journal, Version 2 changes: added acknowledgement to NRAO

Magnetic fields are a good tracer for gas compression by shock waves, which can be caused by interaction of star-formation driven outflows from individual star formation sites as described in the chimney model. We study the magnetic field structure in the central part of the nuclear starburst galaxy NGC 253 with spatial resolutions between 40 and 150 pc to detect any filamentary emission associated with the nuclear outflow. New VLA observations at 3 cm with 7.5" resolution were combined with archive data at 20 and 6 cm. We find filamentary radio continuum emission in a geometrical distribution that we interpret as the boundary of the northwestern nuclear outflow cone. The scaleheight of the continuum emission is 150+/-20 pc, regardless of the observing frequency. The equipartition magnetic field strength is 46+/-10 microG for the total field and 21+/-5 microG for the regular field in the filaments. The ordered magnetic field is aligned along the filaments, in agreement with amplification due to compression. The perpendicular diffusion coefficient across the filaments is kappa_perp = 1.5 x 10^28 cm^2 s^-1 E(GeV)^(0.5+/-0.7). In the SE part of the nuclear outflow cone the magnetic field is pointing away from the disc in form of a helix, with an azimuthal component increasing up to at least 1200 pc height, where it is about equal to the total component. The ordered magnetic field in the disc is anisotropic within a radius of 2.2 kpc. At larger radii, the large-scale field is regular and of even parity. The magnetic field is able to collimate the outflow, which can explain the observed small opening angle of ~26 degree. Due to angular momentum conservation, the field lines are frozen into the plasma and are wound up into a helix. Strong adiabatic losses of the cosmic-ray electrons can partly explain why the radio luminosity of the nucleus lies below the radio-FIR correlation., 18 pages, 17 figures, replaced with version published in Astronomy and Astrophysics

Future radio observations with the SKA and its precursors will be sensitive to trace spiral galaxies and their magnetic field configurations up to redshift $z\approx3$. We suggest an evolutionary model for the magnetic configuration in star-forming disk galaxies and simulate the magnetic field distribution, the total and polarized synchrotron emission, and the Faraday rotation measures for disk galaxies at $z\la 3$. Since details of dynamo action in young galaxies are quite uncertain, we model the dynamo action heuristically relying only on well-established ideas of the form and evolution of magnetic fields produced by the mean-field dynamo in a thin disk. We assume a small-scale seed field which is then amplified by the small-scale turbulent dynamo up to energy equipartition with kinetic energy of turbulence. The large-scale galactic dynamo starts from seed fields of 100 pc and an averaged regular field strength of 0.02\,$\mu$G, which then evolves to a "spotty" magnetic field configuration in about 0.8\,Gyr with scales of about one kpc and an averaged regular field strength of 0.6\,$\mu$G. The evolution of these magnetic spots is simulated under the influence of star formation, dynamo action, stretching by differential rotation of the disk, and turbulent diffusion. The evolution of the regular magnetic field in a disk of a spiral galaxy, as well as the expected total intensity, linear polarization and Faraday rotation are simulated in the rest frame of a galaxy at 5\,GHz and 150\,MHz and in the rest frame of the observer at 150\,MHz. We present the corresponding maps for several epochs after disk formation. (abridged), Comment: 13 pages, 6 figures, 2 tables, revised version is accepted for publication in Astronomische Nachrichten

The face-on spiral galaxy IC 342 is known to possess an axisymmetric spiral magnetic field (ASS) with magnetic field lines being orientated inwards everywhere at least in the analyzed radial range between 5 and 13 kpc1 (Krause et al., 1989a; Sokoloff et al., 1992). The ASS field configuration seems to be even with respect to the galactic plane.