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Drzazga R.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Chyzy K.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Heald G.H.,Netherlands Institute for Radio Astronomy | Heald G.H.,University of Groningen | And 2 more authors.
Astronomy and Astrophysics | Year: 2016

Aims. It is still unknown how magnetic field-generation mechanisms could operate in low-mass dwarf galaxies. Here, we present a detailed study of a nearby pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this galaxy possesses a clearly defined disk. We also discuss whether NGC 2976 could serve as a potential source of the intergalactic magnetic field. Methods. For the purpose of our studies, we performed deep multi-frequency polarimetric observations of NGC 2976 with the VLA and Effelsberg radio telescopes. Additionally, we supplement them with re-imaged data from the WSRT-SINGS survey for which a rotation measure (RM) synthesis was performed. A new weighting scheme for the RM synthesis algorithm, consisting of including information about the quality of data in individual frequency channels, was proposed and investigated. Application of this new weighting to the simulated data, as well as to the observed data, results in an improvement of the signal-to-noise ratio in the Faraday depth space. Results. The magnetic field morphology discovered in NGC 2976 consists of a southern polarized ridge. This structure does not seem to be due to just a pure large-scale dynamo process (possibly cosmic-ray driven) at work in this object, as indicated by the RM data and dynamo number calculations. Instead, the field of NGC 2976 is modified by past gravitational interactions and possibly also by ram pressure inside the M 81 galaxy group environment. The estimates of total (7 μG) and ordered (3 μG) magnetic field strengths, as well as degree of field order (0.46), which is similar to those observed in spirals, suggest that tidally generated magnetized gas flows can further enhance dynamo action in the object. NGC 2976 is apparently a good candidate for the efficient magnetization of its neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic field into the intergalactic space up to a distance of about 5 kpc. Conclusions. Tidal interactions (and possibly also ram pressure) can lead to the formation of unusual magnetic field morphologies (like polarized ridges) in galaxies out of the star-forming disks, which do not follow any observed component of the interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to provide ordered magnetic fields far out of their main disks. © ESO, 2016.


Damas-Segovia A.,MPI fur Radioastronomie | Beck R.,MPI fur Radioastronomie | Vollmer B.,University of Strasbourg | Wiegert T.,Queen's University | And 7 more authors.
Astrophysical Journal | Year: 2016

We investigate the effects of ram pressure on the ordered magnetic field of a galaxy hosting a radio halo and strong nuclear outflows. New radio images in total and polarized intensity of the edge-on Virgo galaxy NGC 4388 were obtained within the CHANG-ES EVLA project. The unprecedented noise level reached allows us to detect striking new features of the ordered magnetic field. The nuclear outflow extends far into the halo to about 5 kpc from the center and is spatially correlated with the Hα and X-ray emission. For the first time, the southern outflow is detected. Above and below both spiral arms we find extended blobs of polarized emission with an ordered field oriented perpendicular to the disk. The synchrotron lifetime of the cosmic-ray electrons (CREs) in these regions yields a mean outflow velocity of 270 ± 70 km s-1, in agreement with a galactic wind scenario. The observed symmetry of the polarized halo features in NGC 4388 excludes a compression of the halo gas by the ram pressure of the intracluster medium (ICM). The assumption of equilibrium between the halo pressure and the ICM ram pressure yields an estimate of the ICM density that is consistent with both the ICM density derived from X-ray observations and the recent Planck Sunyaev-Zel'dovich measurements. The detection of a faint radio halo around cluster galaxies could thus be used for an estimate of ICM ram pressure. © 2016. The American Astronomical Society. All rights reserved.


Jurusik W.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Drzazga R.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Jableka M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Chyz Y K.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | And 3 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. We investigate how magnetic properties of Magellanic-type and perturbed objects are related to star-forming activity, galactic type, and mass. Methods. We present radio and magnetic properties of five Magellanic-type and two peculiar low-mass galaxies observed at 4.85 and/or 8.35 GHz with the Effelsberg 100 m telescope. The sample is extended to 17 objects by including five Magellanic-type galaxies and five dwarf ones. Results. The distribution of the observed radio emission of low-mass galaxies at 4.85/8.35 GHz is closely connected with the galactic optical discs, which are independent for unperturbed galaxies and those which show signs of tidal interactions. The strengths of total magnetic field are within 5-9 μG, while the ordered fields reach 1-2 μG, and both these values are larger than in typical dwarf galaxies and lower than in spirals. The magnetic field strengths in the extended sample of 17 low-mass galaxies are well correlated with the surface density of star formation rate (correlation coefficient of 0.87) and manifest a power-law relation with an exponent of 0.25 ± 0.02 extending a similar relation found for dwarf galaxies. We claim that the production of magnetic energy per supernova event is very similar for all the various galaxies. It constitutes about 3% (10 49 erg) of the individual supernovae energy release. We show that the total magnetic field energy in galaxies is almost linearly related to the galactic gas mass, which indicates equipartition of the magnetic energy and the turbulent kinetic energy of the interstellar medium. The Magellanic-type galaxies fit very well with the radio-infrared relation constructed for surface brightness of galaxies of various types, including bright spirals and interacting objects (with a slope of 0.96 ± 0.03 and correlation coefficient of 0.95). We found that the typical far-infrared relation based on luminosity of galaxies is tighter and steeper but more likely to inherit a partial correlation from a tendency that larger objects are also more luminous. Conclusions. The estimated values of thermal fractions, radio spectral indices, and magnetic field strengths of the Magellanic-type galaxies are between the values determined for grand-design spirals and dwarf galaxies. The confirmed magnetic field-star formation and radio-infrared relations for low-mass galaxies point to similar physical processes that must be at work in all galaxies. More massive, larger galaxies have usually stronger magnetic fields and larger global star formation rates, but we show that their values of magnetic energy release per supernova explosion are still similar to those of dwarf galaxies. © ESO, 2014.


Wezgowiec M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Wezgowiec M.,Ruhr University Bochum | Urbanik M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Beck R.,Max Planck Institute for Radio Astronomy | And 2 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The Virgo cluster of galaxies provides excellent conditions for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated in detail. Aims. We extend our systematic search for possible anomalies in the magnetic field structures of Virgo cluster spirals in order to characterize a variety of effects and attribute them to different disturbing agents. Methods. Six angularly large Virgo cluster spiral galaxies (NGC 4192, NGC 4302, NGC 4303, NGC 4321, NGC 4388, and NGC 4535) were targets of a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz and 8.35 GHz (except for NGC 4388 observed only at 4.85 GHz, and NGC 4535 observed only at 8.35 GHz). The presented two-frequency studies allow Faraday rotation analysis. Results. Magnetic field structures distorted to various extent are found in all galaxies. Three galaxies (NGC 4302, NGC 4303, and NGC 4321) show some signs of possible tidal interactions, while NGC 4388 and NGC 4535 have very likely experienced strong ram-pressure and shearing effects, respectively, visible as distortions and asymmetries of polarized intensity distributions. As in our previous study, even strongly perturbed galaxies closely follow the radio-far-infrared correlation. In NGC 4303 and NGC 4321, we observe symmetric spiral patterns of the magnetic field and in NGC 4535 an asymmetric pattern. Conclusions. The cluster environment clearly affects the evolution of its member galaxies via various effects. Magnetic fields allow us to trace even weak interactions that are difficult to detect with other observations. Our results show that the degree of distortions of a galaxy is not a simple function of the distance to the cluster center but reflects also the history of its interactions. The angle Θ between the velocity vector v and the rotation vector Ω of a galaxy may be a general parameter that describes the level of distortions of galactic magnetic fields. Information about the motions of galaxies in the sky plane and their three-dimensional distribution, as well as information about the intracluster medium can also be obtained from the Faraday rotation analysis. © ESO, 2012.


Wezgowiec M.,Ruhr University Bochum | Bomans D.J.,Ruhr University Bochum | Ehle M.,Newton Science Operations Center | Chyzy K.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | And 3 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Cluster and group spiral galaxies are very often affected by their environment. The hot intracluster/intragroup medium (ICM/IGM) and a high galaxy density can lead to perturbations of the galactic interstellar medium (ISM) due to ram pressure and/or tidal interaction effects. In radio polarimetry observations, both phenomena may manifest similar features. X-ray data can help to determine the real origin of the perturbation. Aims. We analyse the distribution and physical properties of the hot gas in the Virgo cluster spiral galaxies NGC 4254 and NGC 4569, which indicate that the cluster environment has had a significant influence on their properties. By performing both spatial and spectral analyses of X-ray data, we try to distinguish between two major phenomena: tidal and ram pressure interactions. We compare our findings with the case of NGC 2276, in which a shock was reported, by analysing XMM-Newton X-ray data for this galaxy. Methods. We use archival XMM-Newton observations of NGC 4254, NGC 4569, and NGC 2276. Maps of the soft diffuse emission in the energy band 0.2-1 keV are obtained. For the three galaxies, especially at the position of magnetic field enhancements we perform a spectral analysis to derive gas temperatures and thus to look for shock signatures. A shock is a signature of ram pressure resulting from supersonic velocities; weak tidal interactions are not expected to influence the temperature of the ionized gas. Results. In NGC 4254, we do not observe any temperature increase at the position of the bright polarized radio ridge. This suggests that the feature is formed by tidal interactions, and not by ram pressure stripping. NGC 4569 shows a higher temperature at the position of the polarized features, which may be indicative of ram-pressure effects. For NGC 2276, we do not find clear indications of a shock. Although ram-pressure effects seem to be visible, the main driver of the observed distortions is most likely tidal interaction. Conclusions. Determining gas temperatures via sensitive X-ray observations at the position of polarized radio ridges seems to be a good method for distinguishing between ram pressure and tidal interaction effects acting upon a galaxy. © 2012 ESO.


Wezgowiec M.,Ruhr University Bochum | Soida M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Bomans D.J.,Ruhr University Bochum
Astronomy and Astrophysics | Year: 2012

Context. Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. Aims. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. Methods. We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. Results. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. Conclusions. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy. © 2012 ESO.


Wezgowiec M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Jamrozy M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Mack K.-H.,National institute for astrophysics
Acta Astronomica | Year: 2016

This paper presents 1.4-GHz radio continuum observations of fifteen very extended radio galaxies. These sources are so large that most interferometers lose partly their structure and total flux density. Therefore, single-dish detections are required to fill in the central (u,v) gap of interferometric data and obtain reliable spectral index patterns across the structures, and thus also an integrated radio continuum spectrum. We have obtained such 1.4-GHz maps with the 100-m Effelsberg telescope and combined them with the corresponding maps available from the NVSS. The aggregated data allow us to produce high-quality images, which can be used to obtain physical parameters of the mapped sources. The combined images reveal in many cases extended low surface-brightness cocoons.


Chyzy K.T.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Wezgowiec M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Wezgowiec M.,Ruhr University Bochum | Beck R.,Max Planck Institute for Radio Astronomy | Bomans D.J.,Ruhr University Bochum
Astronomy and Astrophysics | Year: 2011

Aims. We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods. We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m Effelsberg telescope at 2.64 GHz. Three galaxies were detected. A higher frequency (4.85 GHz) was used to search for polarized emission in five dwarfs that are the most luminous ones in the infrared domain, of which three were detected. Results. Magnetic fields in LG dwarfs are weak, with a mean value of the total field strength of <4.2 ± 1.8 μG, three times lower than in the normal spirals. The strongest field among all LG dwarfs of 10 μG (at 2.64 GHz) is observed in the starburst dwarf IC 10. The production of total magnetic fields in dwarf systems appears to be regulated mainly by the star-formation surface density (with the power-law exponent of 0.30 ± 0.04) or by the gas surface density (with the exponent 0.47 ± 0.09). In addition, we find systematically stronger fields in objects of higher global star-formation rate. The dwarf galaxies follow a similar far-infrared relationship (with a slope of 0.91 ± 0.08) to that determined for high surface brightness spiral galaxies. The magnetic field strength in dwarf galaxies does not correlate with their maximum rotational velocity, indicating that a small-scale rather than a large-scale dynamo process is responsible for producting magnetic fields in dwarfs. If magnetization of the Universe by galactic outflows is coeval with its metal enrichment, we show that more massive objects (such as Lyman break galaxies) can efficiently magnetize the intergalactic medium with a magnetic field strength of about 0.8 nG out to a distance of 160-530 kpc at redshifts 5-3, respectively. Magnetic fields that are several times weaker and shorter magnetization distances are expected for primordial dwarf galaxies. We also predict that most star-forming local dwarfs might have magnetized their surroundings up to a field strength about 0.1 μG within about a 5 kpc distance. Conclusions. Strong magnetic fields (>6 μG) are observed only in dwarfs of extreme characteristics (e.g. NGC 4449, NGC 1569, and the LG dwarf IC 10). They are all starbursts and more evolved objects of statistically much higher metallicity and global star-formation rate than the majority of the LG dwarf population. Typical LG dwarfs are unsuitable objects for the efficient supply of magnetic fields to the intergalactic medium. © 2011 ESO.


Wezgowiec M.,Ruhr University Bochum | Vollmer B.,11 Rue Of Luniversite | Ehle M.,Newton Science Operations Center | Dettmar R.-J.,Ruhr University Bochum | And 4 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The detailed comparison between observations and simulations of ram-pressure stripped spiral galaxies in the Virgo cluster has led to a 3D view of the galaxy orbits within the hot intracluster medium. The 3D velocities and Mach numbers derived from simulations can be used to derive simple Mach cone geometries for Virgo spiral galaxies. Aims. We search for indications of hot gas within Mach cones in X-ray observations of selected Virgo cluster spiral galaxies (NGC 4569, NGC 4388, and NGC 4501). Methods. Low-resolution maps of diffuse extended emission and X-ray spectra from XMM-Newton observations are presented. Gas densities and temperatures were derived from the X-ray spectra. Results. We find extraplanar diffuse X-ray emission in all galaxies. Based on the 3D velocity vectors from dynamical modeling, a simple Mach cone is fitted to the triangular shape of NGC 4569's diffuse X-ray emission. Assuming that all extraplanar diffuse X-ray emission has to be located inside the Mach cone, we also fit Mach cones to NGC 4388's and NGC 4501's extraplanar X-ray emission. For NGC 4569 it is hard to reconcile the derived Mach cone opening angle with a Mach number based on the sound speed alone. Instead, a Mach number involving the Alfvénic speed seems to be more appropriate, yielding a magnetic field strength of ∼1-3 μG for an intracluster medium density of n ∼ 10 -4 cm-3. Whereas the temperature of the hot component of NGC 4569's X-ray halo (0.5 keV) is at the high end, but typical of a galactic outflow, the temperature of the hot gas tails of NGC 4388 and NGC 4501 are significantly hotter (0.7-C0.9 keV). Conclusions. In NGC 4569 we find direct evidence of a Mach cone that is filled with hot gas from a galactic superwind. We suggest that the high gas temperatures in the X-ray tails of NGC 4388 and NGC 4501 come from the mixing of the stripped ISM into the hot intracluster medium of the Virgo cluster. © 2011 ESO.


Nikiel-Wroczynski B.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Soida M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Urbanik M.,Obserwatorium Astronomiczne Uniwersytetu Jagiellonskiego | Wezgowiec M.,Ruhr University Bochum | And 3 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The Leo Triplet group of galaxies is best known for the impressive bridges of neutral gas that connect its members. One of the bridges forms a large tidal tail extending eastwards from NGC 3628 that hosts several H i plumes and carries the material from this galaxy to the intergalactic space. Aims. The magnetic fields of the member galaxies NGC 3628 and NGC 3627 show morphological peculiarities, suggesting that interactions within the group may be caused by stripping of the magnetic field. This process could supply the intergalactic space with magnetised material, a scenario considered as a possible source of intergalactic magnetic fields (as seen eg. in the "Taffy" pairs of galaxies). Additionally, the plumes are likely to be the tidal dwarf galaxy candidates. Methods. We performed radio continuum mapping observations at 2.64 GHz using the 100-m Effelsberg radio telescope. We obtained total power and polarised intensity maps of the Triplet. These maps were analysed together with the archive data, and the magnetic field strength (as well as the magnetic energy density) was estimated. Results. Extended emission was not detected either in the total power or the polarised intensity maps. We obtained upper limits of the magnetic field strength and the energy density of the magnetic field in the Triplet. We detected emission from the easternmost clump and determined the strength of its magnetic field. In addition, we measured integrated fluxes of the member galaxies at 2.64 GHz and estimated their total magnetic field strengths. Conclusions. We found that the tidal tail hosts a tidal dwarf galaxy candidate that possesses a detectable magnetic field with a non-zero ordered component. Extended radio continuum emission, if present, is weaker than the reached confusion limit. The total magnetic field strength does not exceed 2.8 μG and the ordered component is lower than 1.6 μG. © 2013 ESO.

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