12 research outputs found
Multifrequency analysis of the radio emission from a post-merger galaxy CGCG 292-057
Galaxies exhibiting a specific large-scale extended radio emission, such as
X-shaped radio galaxies, belong to a rare class of winged radio galaxies. The
morphological evolution of these radio sources is explained using several
theoretical models, including galaxy mergers. However, such a direct link
between a perturbed radio morphology and a galaxy merger remains
observationally sparse. Here we investigate a unique radio galaxy J1159+5820,
whose host CGCG 292-057 displays the optical signature of a post-merger system
with a distinct tidal tail feature, and an X-shaped radio morphology
accompanied by an additional pair of inner lobes. We observed the target on a
wide range of radio frequencies ranging from 147 MHz to 4959 MHz, using
dedicated GMRT and VLA observations, and supplemented it with publicly
available survey data for broadband radio analysis. Particle injection models
were fitted to radio spectra of lobes and different parts of the wings.
Spectral ageing analysis performed on the lobes and the wings favors a fast jet
realignment model with a reorientation timescale of a few million years. We
present our results and discuss the possible mechanisms for the formation of
the radio morphology.Comment: 13 pages, 9 figures, Accepted for publication in MNRA
Dynamical analysis of the complex radio structure in 3C 293 : clues on a rapid jet realignment in X-shaped radio galaxies
Context. Radio galaxies classified as X-shaped/winged, are characterised
by two pairs of extended and misaligned lobes, which suggest a rapid realignment of the
jet axis, for which a potential cause (including binary supermassive black holes, a black
hole merger, or a Lense-Thirring precession) is still under debate.
Aims. Here we analyse the complex radio structure of 3C 293 winged
source hosted by the post-merger galaxy UGC 8782, which uniquely displays a significant
asymmetry between the sizes (and therefore the ages) of the two pairs of lobes, indicating
that an episode of jet realignment took place only very recently. This allows us to
tightly constrain the corresponding timescales, and therefore to discriminate between
different models proposed for the formation of X-shaped radio galaxies in general.
Methods. Based on all the available and carefully re-analysed radio data
for 3C 293, we have performed a detailed spectral modelling for the older and younger
lobes in the system, using the existing evolutionary DYNAGE algorithm. In this way we
derived the lobes’ ages and jet energetics, which we then compared to the accretion power
in the source.
Results. We found that the 200 kpc-scale outer lobes of 3C 293 are ~ 60 Myr old and, until very recently,
have been supplied with fresh electrons and magnetic field by the jets, i.e., jet activity
related to the formation of the outer lobes ceased within the last Myr. Meanwhile, the
inner 4 kpc-scale lobes, tilted by ~
40° with respect to the outer ones, are only about ~ 0.3 Myr old. Interestingly, the best
model fits also return identical values of the jet power supplying the outer and the inner
structures. This power, moreover, is of the order of the maximum kinetic luminosity of a
Blandford-Znajek jet for a given black hole mass and accretion rate, but only in the case
of relatively low values of a black hole spin, a ~ 0.2.
Conclusions. The derived jet energetics and timescales, along with the
presence of two optical nuclei in UGC 8782, all provide a strong support to the
Lense-Thirring precession model in which the supermassive black hole spin, and therefore
the jet axis, flips rapidly owing to the interactions with the tilted accretion disk in a
new tidal interaction episode of the merging process. We further speculate that, in
general, X-shape radio morphology forms in post-merger systems that are rich in cold
molecular gas, and only host slowly spinning supermassive black holes
Hot gas and magnetic arms of NGC 6946 : indications for reconnection heating?
Context. The grand-design face-on spiral galaxy NGC 6946 is remarkable because of its high star formation activity, the massive northern spiral arm, and the magnetic arms, which are observed in polarized radio synchrotron emission and are located between the optical arms and possibly are magnetic reconnection regions. Aims. We used electron densities and temperatures in star-forming (active) and less active regions and compared them to findings from the analysis of the radio data to study the energy budget of NGC 6946. The hot gas above the magnetic arms between the optical arms might suggest gas heating by reconnection. We also study the population of point sources in NGC 6946, including the origin of the puzzling ultra-luminous emission complex MF16. Methods. X-ray observations of NGC 6946 performed with XMM-Newton were used to study the emission from X-ray point sources and diffuse hot gas, including the magnetic arms and the halo. Spectral fitting of the diffuse X-ray emission allowed us to derive temperatures of the hot gas. With assumptions about the emission volume, this allowed us to estimate gas densities, masses, and cooling times. Results. To explain the X-ray emission from the spiral arms of NGC 6946 two-temperature plasma models are needed to account for the disk and halo emission. The interarm regions show only one thermal component. We observe that the temperature of the hot gas in and above the magnetic arm regions increases slightly when compared to the average temperatures in the areas in and above the spiral arms. For the southwestern part of the disk, which is depolarized in the radio range by Faraday rotation, we find more efficient mixing of disk and halo gas. Conclusions. We propose magnetic reconnection in the magnetic arm regions of NGC 6946 as the possible cause of the additional heating of the gas and ordering of the magnetic fields. In the southwestern part of the galactic disk we observed indications of a possible faster outflow of the hot gas. A very hot gas within the MF 16 nebula possibly suggests shock heating by a supernova explosion
Magnetic fields and hot gas in M 101
Context. Studies of nearby spiral galaxies in radio and X-ray wavelengths reveal the structure and energy balance of the magnetic fields and the hot interstellar medium (ISM). In some spiral galaxies, large-scale ordered magnetic fields have been found between the spiral stellar arms (the so-called magnetic arms). One of the considered explanations of their origin is magnetic reconnection, which according to theoretical studies can efficiently heat the low-density ISM.
Aims. We present, for the first time, high-resolution C-band (5 GHz) radio maps of the nearby face-on spiral galaxy M 101 to study the magnetic fields and verify the existence of the magnetic arms. The analysis of the archival XMM-Newton X-ray data is performed to search for signatures of gas heating by magnetic reconnection effects in the disk and the halo of this galaxy.
Methods. We combine the Very Large Array (VLA) and Effelsberg radio maps of M 101 to restore the large-scale emission lost in the interferometric observations. From the obtained maps, we derive magnetic field strengths and energy densities, and compare them with the properties of the hot gas found with the spectral analysis of the X-ray data.
Results. Most of the X-ray emission likely comes from the hot gas in the halo of M 101. Its temperature is highest above the massive stellar arm and an inter-arm region with enhanced polarised radio emission, as well as in the inter-arm area where neither Hα nor H
Hot magnetic halo of NGC 628 (M 74)
Context. In several spiral galaxies that are observed face-on, large-scale ordered magnetic fields (the so-called magnetic arms) were found. One of the explanations was the action of the magnetic reconnection, which leads to a higher ordering of the magnetic fields. Because it simultaneously converts the energy of the magnetic fields into thermal energy of the surroundings, magnetic reconnection has been considered as a heating mechanism of the interstellar medium for many years. Until recently, no clear observational evidence for this phenomenon was found. Aims. We search for possible signatures of gas heating by magnetic reconnection effects in the radio and X-ray data for the face-on spiral galaxy NGC 628 (M 74), which presents pronounced magnetic arms and evidence for vertical magnetic fields. Methods. The strengths and energy densities of the magnetic field in the spiral and magnetic arms were derived, as were the temperatures and thermal energy densities of the hot gas, for the disk and halo emission. Results. In the regions of magnetic arms, higher order and lower energy density of the magnetic field is found than in the stellar spiral arms. The global temperature of the hot gas is roughly constant throughout the disk. Conclusions. The comparison of the findings with those obtained for the starburst galaxy M 83 suggests that magnetic reconnection heating may be present in the halo of NGC 628. The joint analysis of the properties of the magnetic fields and the hot gas in NGC 628 also provided clues for possible tidal interaction with the companion galaxy
Magnetic fields and star formation in low-mass Magellanic-typeand peculiar galaxies
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% (1049 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
Hot gas heating via magnetic arms in spiral galaxies. The case of M 83
Context. Reconnection heating has been considered as a potential source of the heating of the interstellar medium. In some galaxies, significant polarised radio emission has been found between the spiral arms. This emission has a form of “magnetic arms” that resembles the spiral structure of the galaxy. Reconnection effects could convert some of the energy of the turbulent magnetic field into the thermal energy of the surrounding medium, leaving more ordered magnetic fields, as is observed in the magnetic arms.
Aims. Sensitive radio and X-ray data for the grand-design spiral galaxy M 83 are used for a detailed analysis of the possible interactions of magnetic fields with hot gas, including a search for signatures of gas heating by magnetic reconnection effects.
Methods. Magnetic field strengths and energies derived from the radio emission are compared with the parameters of the hot gas calculated from the model fits to sensitive X-ray spectra of the hot gas emission.
Results. The available X-ray data allowed us to distinguish two thermal components in the halo of M 83. We found slightly higher average temperatures of the hot gas in the interarm regions, which results in higher energies per particle and is accompanied by a decrease in the energy density of the magnetic fields.
Conclusions. The observed differences in the energy budget between the spiral arms and the interarm regions suggest that, similar to the case of another spiral galaxy NGC 6946, we may be observing hints for gas heating by magnetic reconnection effects in the interarm regions. These effects, which act more efficiently on the turbulent component of the magnetic field, are expected to be stronger in the spiral arms. However, with the present data it is only possible to trace them in the interarm regions, where the star formation and the resulting turbulence is low