arXiv subjects

M. Soida

Publications and source records attributed to M. Soida.

At least 19 recordsLinked to original sources

arXiv2026

Predicting CO and dust emission of star-forming galaxies

How do Dwarf Galaxies differ from spirals? Does star formation produce radio and far-infrared emission in the same way as in spiral galaxies? Radio, FarIR, and CO emission depend on gas density, temperature, magnetic field strength, and metallicity. The radio-FarIR correlation and Schmidt-Kennicutt relation characterize the links for Milky Way-like galaxies but do they hold for smaller objects, with different morphologies? Here we extend our previous work on the IR, line, and radio emission of local and high-z galaxies to local star-forming low-mass and dwarf galaxies. The calculation of the cosmic ray (CR) densities were improved compared to the previous version of the model. The CR ionization rate we found for the different galaxy samples is higher by a factor of three than for the solar neighborhood. This means that the mean yield of low-energy CR particles three times higher in external galaxies than was observed by Voyager I. The dependence of the N_H2/I_CO factor on the metallicity and stellar mass are calculated by the model. The weaker CO emission from low-metallicity galaxies is due to the large amount of (CO-dark) H_2 surrounding the regions where CO is not photo-dissociated. Within our model framework, star-forming low-mass and dwarf galaxies follow the radio-IR correlation.

astro-ph.GA↗

arXiv2025

Deciphering the radio-star formation correlation on kpc scales. IV. Radio halos of highly-inclined Virgo cluster spiral galaxies

In addition to the radio continuum emission of the thin galactic disk, vertically extended emission is ubiquitous in starforming disk galaxies. This halo emission can represent an important fraction of the total emission of the galaxy The cosmic ray electrons (CRe) responsible for the radio continuum emission are produced within the thin disk and transported into the halo. We made an attempt to reconstruct the radial properties of radio continuum halos in nearly edge-on galaxies where the star formation rate (SFR) distribution can be deprojected and the vertical radio continuum emission is well distinct from the disk emission. The deprojected SFR distribution is convolved with a Gaussian kernel to take CRe diffusion within the galactic disk into account and a vertical profile of the radio continuum emissivity is added to the disk emission. The three-dimensional emission distribution is then projected on the sky and compared to VLA radio continuum observations at 20 and 6 cm. We found that overall the halo emission contains information on the underlying distribution of the star formation rate. The majority of our galaxies show flaring radio continuum halos. Except for one galaxy, our Virgo galaxies follow the trend of increasing effective height with increasing radio continuum size found by the CHANG-ES collaboration. We confirm that radio continuum halos can represent a significant fraction of the total radio continuum emission of a starforming spiral galaxy. At 20 cm and 6 cm between 30 and 70 of the total radio continuum emission originate in the halo. We propose a halo classification based on the height ratio and SI between 20 and 6cm. If we interpret the vertical structures of the large-scale magnetic field within the disk-halo and halo types as a sign of a galactic outflow or wind, all galaxies except one most probably harbor an advection-dominated halo.

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arXiv2024

Predicting HCN, HCO$^+$, multi-transition CO, and dust emission of star-forming galaxies -- Extension to luminous infrared galaxies and the role of cosmic ray ionization

The specific star-formation rate of star-forming `main sequence' galaxies significantly decreased since z~1.5, due to the decreasing molecular gas fraction and star formation efficiency. However, the radio-infrared (IR) correlation has not changed significantly since z~1.5. The theory of turbulent clumpy starforming gas disks together with the scaling relations of the interstellar medium describes the large and small-scale properties of galactic gas disks. Here we extend our previous work on infrared, multi-transition molecular line, and radio continuum emission of local and high-z starforming and starburst galaxies to local and z~0.5 luminous infrared galaxies. The model reproduces the IR luminosities, CO, HCN, and HCO+ line luminosities, and the CO spectral line energy distributions of these galaxies. We derive CO(1-0) and HCN(1-0) conversion factors for all galaxy samples. The relation between the star formation rate per unit area and H2 surface density cannot be fit simply for all redshifts. There is a tight correlation between the star formation efficiency and the product of the gas turbulent velocity dispersion and the angular velocity of the galaxies. Galaxies of lower stellar masses can in principle compensate their gas consumption via star formation by radial viscous gas accretion. The limiting stellar mass increases with redshift. Whereas the radio continuum emission is directly proportional to the density of cosmic ray (CR) electrons, the molecular line emission depends on the CR ionization rate via the gas chemistry. The normalization of the CR ionization rate found for the different galaxy samples is about a factor of three to five higher than the normalization for the Solar neighborhood. This means that the mean yield of low energy CR particles for a given star formation rate per unit area is about three to ten times higher in external galaxies than observed by Voyager I.

astro-ph.GA↗

arXiv2024

CHANG-ES XXXIV: a 20 kpc radio bubble in the halo of the star-forming galaxy NGC 4217

Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider's view of the radio halo, which shows the presence of extra-planar cosmic-ray electrons and magnetic fields. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC 4217 in order to study the distribution of extra-planar cosmic rays and magnetic fields. We both observe with the Jansky Very Large Array (JVLA) in the S-band (2-4 GHz) and with LOw Frequency ARray (LOFAR) at 144 MHz. We measure vertical intensity profiles and exponential scale heights. We re-image both JVLA and LOFAR data at matched angular resolution in order to measure radio spectral indices between 144 MHz and 3 GHz. Confusing point-like sources were subtracted prior to imaging. Intensity profiles are then fitted with cosmic-ray electron advection models, where we use an isothermal wind model that is driven by a combination of pressure from the hot gas and cosmic rays. We discover a large-scale radio halo on one (northwestern) side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20 kpc away from the disc. We find spectral ageing in the bubble which allows us to measure advection speeds of the cosmic-ray electrons accelerating from 300 to 600 $\rm km\, s^{-1}$ . Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble can be inflated by a modest 10 per cent of the kinetic energy injected by supernovae over its dynamical time-scale of 35 Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Non-thermal bubbles with sizes of tens of kiloparsec may be a ubiquitous feature of star-forming galaxies showing the influence of feedback. To determine possible contributions by AGN feedback, will require deeper observations.

astro-ph.GA↗

arXiv2023

Deciphering the radio-star formation correlation on kpc-scales III. Radio-dim and bright regions in spiral galaxies

The relation between the resolved star formation rate per unit area and the non-thermal radio continuum emission is studied in 21 Virgo cluster galaxies and the two nearby spiral galaxies, NGC6946 and M51. For the interpretation and understanding of our results we used a 3D model where star formation, 2D cosmic ray (CR) propagation, and the physics of synchrotron emission are included. Based on the linear correlation between the star formation rate per unit area and the synchrotron emission and its scatter radio-bright and radio-dim regions can be robustly defined for our sample of spiral galaxies. We identified CR diffusion or streaming as the physical causes of radio-bright regions of unperturbed symmetric spiral galaxies as NGC6946. We identified the probable causes of radio-bright regions in several galaxies as CR transport, via either gravitational tides (M51) or galactic winds (NGC4532) or ram pressure stripping (NGC4330 and NGC4522). Three galaxies are overall radio-dim: NGC4298, NGC4535, and NGC4567. Based on our model of synchrotron-emitting disks we suggest that the overall radio-dim galaxies have a significantly lower magnetic field than expected by equipartition between the magnetic and turbulent energy densities. Radio-bright regions frequently coincide with asymmetric ridges of polarized radio continuum emission, and we found a clear albeit moderate correlation between the polarized radio continuum emission and the radio/SFR ratio. When compression or shear motions of the interstellar medium (ISM) are present in the galactic disk, the radio-bright regions are linked to the commonly observed asymmetric ridges of polarized radio continuum emission and represent a useful tool for the interaction diagnostics. Based on our results, we propose a scenario for the interplay between star formation, CR electrons, and magnetic fields in spiral galaxies.

astro-ph.GA↗

arXiv2022

Hot magnetic halo of NGC628 (M74)

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. 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 NGC628 (M74), which presents pronounced magnetic arms and evidence for vertical magnetic fields. 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. 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. The comparison of the findings with those obtained for the starburst galaxy M83 suggests that magnetic reconnection heating may be present in the halo of NGC628. The joint analysis of the properties of the magnetic fields and the hot gas in NGC628 also provided clues for possible tidal interaction with the companion galaxy.

astro-ph.GA↗

arXiv2022

Deciphering the radio star formation correlation on kpc scales II. The integrated infrared-radio continuum and star formation - radio continuum correlations

Given the multiple energy loss mechanisms of cosmic ray electrons in galaxies, the tightness of the infrared - radio continuum correlation is surprising. We extended the analytical model of galactic disks of Vollmer et al. (2017) by including a simplified prescription for the synchrotron emissivity. The galactic gas disks of local spiral galaxies, low-z starburst galaxies, high-z main sequence starforming, and high-z starburst galaxies are treated as turbulent clumpy accretion disks. The magnetic field strength is determined by the equipartition between the turbulent kinetic and the magnetic energy densities. Our fiducial model, which neither includes galactic winds nor CR electron secondaries, reproduces the observed radio continuum SEDs of most (~70%) of the galaxies. Except for the local spiral galaxies, fast galactic winds can potentially make the conflicting models agree with observations. The observed IR - radio correlations are reproduced by the model within 2 sigma of the joint uncertainty of model and data for all datasets. The model agrees with the observed SFR - radio correlations within ~4 sigma. Energy equipartition between the CR particles and the magnetic field only approximately holds in our models of main sequence starforming galaxies. If a CR electron calorimeter is assumed, the slope of the IR - radio correlation flattens significantly. Inverse Compton (IC) losses are not dominant in the starburst galaxies because in these galaxies not only the gas density but also the turbulent velocity dispersion is higher than in normally starforming galaxies. Equipartition between the turbulent kinetic and magnetic field energy densities then leads to very high magnetic field strengths and very short synchrotron timescales. The exponents of our model SFR - radio correlations at 150 MHz and 1.4 GHz are very close to one.

astro-ph.GA↗

arXiv2022

Magnetic fields and hot gas in M101

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. We present, for the first time, high-resolution C-band (5GHz) radio maps of the nearby face-on spiral galaxy M101 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. We combine the Very Large Array (VLA) and Effelsberg radio maps of M101 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. Most of the X-ray emission likely comes from the hot gas in the halo of M101. 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 Halpha nor HI emission is visible. In regions outside of the spiral arms lower strengths, energy densities and higher orders of the magnetic fields were observed. Although M101 does not possess well-defined magnetic arms, a rudimentary magnetic arm was identified in one of the inter-arm regions. We found weak signatures of additional heating of the ISM there, as well as in the galactic halo, which could be explained by the action of magnetic reconnection.

astro-ph.GA↗

arXiv2021

Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline

[abridged] The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2,000 km, LOFAR has the unique capability of achieving sub-arcsecond resolution at frequencies below 200 MHz, although this is technically and logistically challenging. Here we present a calibration strategy that builds on previous high-resolution work with LOFAR. We give an overview of the calibration strategy and discuss the special challenges inherent to enacting high-resolution imaging with LOFAR, and describe the pipeline, which is publicly available, in detail. We demonstrate the calibration strategy by using the pipeline on P205+55, a typical LOFAR Two-metre Sky Survey (LoTSS) pointing. We perform in-field delay calibration, solution referencing to other calibrators, self-calibration, and imaging of example directions of interest in the field. For this specific field and these ionospheric conditions, dispersive delay solutions can be transferred between calibrators up to ~1.5 degrees away, while phase solution transferral works well over 1 degree. We demonstrate a check of the astrometry and flux density scale. Imaging in 17 directions, the restoring beam is typically 0.3" x 0.2" although this varies slightly over the entire 5 square degree field of view. We achieve ~80 to 300 $\mu$Jy/bm image rms noise, which is dependent on the distance from the phase centre; typical values are ~90 $\mu$Jy/bm for the 8 hour observation with 48 MHz of bandwidth. Seventy percent of processed sources are detected, and from this we estimate that we should be able to image ~900 sources per LoTSS pointing. This equates to ~3 million sources in the northern sky, which LoTSS will entirely cover in the next several years. Future optimisation of the calibration strategy for efficient post-processing of LoTSS at high resolution (LoTSS-HR) makes this estimate a lower limit.

astro-ph.IM↗

arXiv2020

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE). VIII. Modeling ram pressure stripping of diffuse gas in the Virgo cluster spiral galaxy NGC 4330

NGC 4330 is one of the Virgo galaxies whose UV distribution shows a tail structure. An associated tail structure is also observed in the HI and H$\alpha$ emission distributions. Previous dynamical modeling showed that the galaxy is approaching the cluster center and is therefore undergoing increasing ram pressure stripping. Recent stellar population fitting of deep optical spectra together with multiband photometry lead to the determination of the time when star formation was quenched in the galactic disk. We introduce a new version of the dynamical model that includes the diffuse ionized gas and aim to reproduce the HI, H$\alpha$, UV distributions together with the star formation histories of the outer gas-free parts of the galactic disk. The results of 50 simulations with five different Lorentzian temporal ram-pressure profiles and five different delays between the simulation onset and peak ram pressure are presented. The inclusion of diffuse gas stripping changes significantly the HI, UV, and H$\alpha$ emission distributions. The simulations with diffuse gas stripping naturally lead to vertical low surface density filaments in the downwind region of the galactic disk. These filaments occur less frequently in the simulations without diffuse gas stripping. The simulations with diffuse gas stripping lead to better joint fits to the SEDs and optical spectra. The HI, NUV, and H$\alpha$ morphologies of the model snapshots which best reproduce the SEDs and optical spectra are sufficiently different to permit a selection of best-fit models. We conclude that the inclusion of diffuse gas stripping significantly improves the resemblance between the model and observations. Our preferred model yields a time to peak ram pressure of 140 Myr in the future. The spatial coincidence of the radio continuum and diffuse H$\alpha$ tails suggests that both gas phases are stripped together.

astro-ph.GA↗

arXiv2020

Hot gas heating via magnetic arms in spiral galaxies. The case of M 83

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. 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. 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. 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. 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.

astro-ph.GA↗

arXiv2020

LOFAR 144-MHz follow-up observations of GW170817

We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO-Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13.7 degrees when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130-138 and 371-374 days after the merger event, we obtain 3$\sigma$ upper limits for the afterglow component of 6.6 and 19.5 mJy beam$^{-1}$, respectively. Using our best upper limit and previously published, contemporaneous higher-frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha^{610}_{144} \gtrsim -2.5$. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.

astro-ph.HE↗

arXiv2020

Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies

The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are called the A-team. Their flux densities at ultra-low frequencies (<100 MHz) can reach several thousands of janskys, and they often contaminate observations of the low-frequency sky by interfering with image processing. Furthermore, these sources are foreground objects for all-sky observations hampering the study of faint signals, such as the cosmological 21 cm line from the epoch of reionisation. We aim to produce robust models for the surface brightness emission as a function of frequency for the A-team sources at ultra-low frequencies. These models are needed for the calibration and imaging of wide-area surveys of the sky with low-frequency interferometers. This requires obtaining images at an angular resolution better than 15 arcsec with a high dynamic range and good image fidelity. We observed the A-team with the Low Frequency Array (LOFAR) at frequencies between 30 MHz and 77 MHz using the Low Band Antenna (LBA) system. We reduced the datasets and obtained an image for each A-team source. The paper presents the best models to date for the sources Cassiopeia A, Cygnus A, Taurus A, and Virgo A between 30 MHz and 77 MHz. We were able to obtain the aimed resolution and dynamic range in all cases. Owing to its compactness and complexity, observations with the long baselines of the International LOFAR Telescope will be required to improve the source model for Cygnus A further.

astro-ph.HE↗

arXiv2019

Deciphering the radio-star formation correlation on kpc-scales I. Adaptive kernel smoothing experiments

(abridged) Within nearby galaxies, variations in the radio-FIR correlation have been observed, mainly because the cosmic ray electrons migrate before they lose their energy via synchrotron emission or escape. The major cosmic ray electron transport mechanisms within the plane of galactic disks are diffusion and streaming. A predicted radio continuum map can be obtained by convolving the map of comic ray electron sources, represented by that of the star formation, with adaptive Gaussian and exponential kernels. The ratio between the smoothing lengthscales at 6cm and 20cm can be used to distinguish between diffusion and streaming as the dominant transport mechanism. Star formation maps of eight rather face-on local and Virgo cluster spiral galaxies were constructed from Spitzer and Herschel infrared and GALEX UV observations.These maps were convolved with adaptive Gaussian and exponential smoothing kernels to obtain model radio continuum emission maps. It is found that in asymmetric ridges of polarized radio continuum emission the total power emission is enhanced with respect to the star formation rate. The typical lengthscale for the transport of cosmic ray electrons is l=0.9kpc at 6cm and l=1.8kpc at 20cm. Perturbed spiral galaxies tend to have smaller lengthscales. This is a natural consequence of the enhancement of the magnetic field caused by the interaction. The discrimination between the two cosmic ray electron transport mechanisms, diffusion and streaming, is based on (i) the convolution kernel (Gaussian or exponential),(ii) the dependence of the smoothing kernel on the local magnetic field and hence on the local star formation rate, (iii) the ratio between the two smoothing lengthscales via the frequency-dependence of the smoothing kernel, and (iv) the dependence of the smoothing kernel on the ratio between the ordered and the turbulent magnetic field.

astro-ph.GA↗

arXiv2019

CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 - indication of a reversing disk magnetic field

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.

astro-ph.GA↗

arXiv2018

Megaparsec-scale Radio Structure Associated with a Hybrid Blazar SBS B1646+499: Episodic Jet Activity with Precessing Axis

Here we report on the total-intensity 610 MHz GMRT observations of the peculiar hybrid blazar SBS B1646+499, which merges the properties of BL Lacertae objects and flat-spectrum radio quasars. The complex radio structure of SBS B1646+499, emerging from the archival radio data and our new GMRT observations, consists of the Mpc-scale, elongated halo, the unilateral kpc-scale jet, and the nuclear jet extending up to 20pc from the compact core. The giant halo is characterized by a steep radio spectrum, indicative of the advanced ageing of the electron population within the lobes. For the large-scale jet, we detected a spectral gradient along and across the outflow, and in particular spectral flattening of the radio continuum toward the jet edges, suggestive of the spine--boundary shear layer morphology. The nuclear jet displays superluminal knots emerging from the self-absorbed and variable radio core. We interpret all these findings in the framework of the model of an episodic jet activity with a precessing jet axis.

astro-ph.HE↗

arXiv2018

The uneven sisters I, NGC 4388 - a strongly constrained ram pressure stripping event

Since the Virgo cluster is the closest galaxy cluster in the northern hemisphere, galaxy interactions can be observed in it with a kpc resolution. The spiral galaxy NGC 4388 underwent a ram pressure stripping event ~200 Myr ago caused by its highly eccentric orbit within the Virgo cluster. This galaxy fulfills all diagnostic criteria for having undergone active ram pressure stripping in the recent past: a strongly truncated HI and Halpha disk, an asymmetric ridge of polarized radio continuum emission, extended extraplanar gas toward the opposite side of the ridge of polarized radio continuum emission, and a recent (a few 100 Myr) quenching of the star formation activity in the outer, gas-free galactic disk. We made dynamical simulations of the ram pressure stripping event to investigate the influence of galactic structure on the observed properties of NGC 4388. The combination of a deep optical spectrum of the outer gas-free region of the galactic disk together with deep HI, Halpha, FUV, and polarized radio continuum data permits to constrain numerical simulations to derive the temporal ram pressure profile, the 3D velocity vector of the galaxy, and the time since peak ram pressure with a high level of confidence. From the simulations an angle between the ram pressure wind and the galactic disk of 30 degrees is derived. The galaxy underwent peak ram pressure ~240 Myr ago. The observed asymmetries in the disk of NGC 4388 are not caused by the present action of ram pressure, but by the resettling of gas that has been pushed out of the galactic disk during the ram pressure stripping event. For the detailed reproduction of multi-wavelength observations of a spiral galaxy that undergoes or underwent a ram pressure stripping event, galactic structure, i.e. spiral arms, has to be taken into account.

astro-ph.GA↗

arXiv2018

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with CMEs and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with LOFAR, opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon.

astro-ph.SR↗