arXiv subjects

V. Heesen

Publications and source records attributed to V. Heesen.

At least 19 recordsLinked to original sources

arXiv2026

CHANG-ES XL: Magnetic Field Structures in the Disk and Halo of NGC 891

We present new Karl G. Jansky Very Large Array S-band (2-4 GHz) observations of the edge-on spiral galaxy NGC 891, complemented by C-band data, to investigate the structure of its radio continuum halo. Using rotation measure synthesis we detected an extended polarized halo, with most spatially extended polarized emission confined to Faraday depths within +/- 150 rad m-2. We identified a localized region in the north-east side of the galaxy that shows an enhancement in polarized intensity (not in percentage polarization). By combining the radio data with H-alpha and diffuse X-ray maps, we discuss a possible origin for this structure: a superbubble powered by clustered supernovae. Across the disk and halo, the percentage polarization decreases toward the midplane but shows a mild wavelength dependence, despite the edge-on orientation of NGC 891. This behavior implies that the depolarization cannot be dominated by small-scale Faraday rotation within the disk. Instead, it is possible that most of the observed polarized emission arises on the Earth-facing side of the galaxy. Our peak rotation measure (RM) map shows a smooth transition along the major axis, consistent with a large scale axisymmetric magnetic field. Using H-alpha and UV data, we analyzed the distribution of H II regions and found that they are parts of different spiral arms. We also identified a faint, isolated H II region at a galactocentric radius of 16.9 kpc, with both H-alpha and far-UV counterparts, indicating star formation outside the thin disk.

astro-ph.GA↗

arXiv2026

Nearby galaxies in the LOFAR Two-metre Sky Survey IV. A fundamental plane of the radio-SFR relation

Radio continuum emission has the potential to be an extinction-free tracer of star formation. However, the relation between radio continuum luminosity and star formation rate, the radio-SFR relation, is affected by various effects such as cosmic-ray transport, free-free absorption, and cosmic-ray electron energy losses. We aim to calibrate the radio-SFR relation in a sample of nearby galaxies ranging from dwarf to spiral galaxies covering nearly five orders of magnitude in SFR range. We include, both, global (individual galaxies) and local (kiloparsec sized) measurements. We measured radio continuum luminosities at $144\,\rm MHz$ using observations with the LOw Frequency ARray (LOFAR) and measure radio spectral indices using ancillary $1.4\,\rm GHz$ data. Selecting 70 nearby (distance $d < 30\,\rm Mpc$) galaxies, 15 of which were used for local measurements, with rich ancillary data we present a study of the radio-SFR relation using total infrared, mid-infrared, H$\alpha$, and far-ultraviolet as complementary SFR tracers. About one third of our sample are at least moderately star-forming edge-on galaxies with the remaining ones chosen to be a representative sample of a wide range of morphological types and SFR values. For the first time, we show that the radio luminosity ($L_{144}$), the star-formation rate (SFR), and the radio spectral index ($\alpha$) define a 'fundamental plane' in the [$\log(L_{144})$, $\log(\rm SFR)$, $\alpha$] space. This allows us to define a unified radio-SFR relation that works both for global and local data when using the radio spectral index as a second parameter. A unified radio-SFR relation for, both, global and local data may serve as a litmus test for galaxy simulations that include the effect of cosmic rays and magnetic fields. It also strengthens the case for using the radio-SFR relation as an extinction-free tracer of star formation.

astro-ph.GA↗

arXiv2026

CHANG-ES XXXIX. Magnetic field structure in edge-on galaxies: Stacking Stokes parameters

Galactic magnetic fields regulate star formation and cosmic-ray (CR) transport, and understanding their three-dimensional structure, particularly in star-forming late-type galaxies, is key to constraining galactic CR transport. We explore the validity of stacking Stokes $Q$ and $U$ spectra, to infer about the intrinsic polarisation characteristics of star-forming galaxies. To prepare the stacking experiment, we align, scale, convolve, and reproject $C$-band (6 GHz) Stokes $Q$ and Stokes $U$ cubes of 27 star-forming late-type edge-on galaxies. On the stacked cubes, we perform RM-synthesis and discuss the derived polarised intensity (PI), polarisation angle ($\chi_0$), and RM maps. Synthetic data tests demonstrate that stacking Stokes $Q$ and $U$ spectra is valid for tightly constrained underlying distributions of PI, $\chi_0$, and RM. For underlying PI, $\chi_0$, and RM distributions that represent star-forming galaxies, stacking introduces a systematic uncertainty of $\delta_\mathrm{RM}^\mathrm{sys}=90 \mathrm{rad m^{-2}}$ and significantly underestimates the recovered PI. Stacking results reveal a clear X-shaped pattern in the polarisation plane, consistent with prior findings, detecting polarised emission up to 9 kpc above the galactic disc. We find stronger PI on the approaching side of galaxies. Furthermore, we find a decrease in PI in the galactic halo of $\sim 60$% near the galaxy's minor axis. A global RM pattern, as reported in a previous study, cannot be confirmed. Based on our analysis, we present stacking of Stokes $Q$ and Stokes $U$ cubes as an effective tool to recover faint polarised emission in the halo of nearby galaxies, if the underlying distributions of PI, $\chi_0$, and RM are tightly constrained. Our findings motivate future studies using broader-band data to increase the resolution in Faraday depth.

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arXiv2026

The LOFAR Two-metre Sky Survey: VII. Third Data Release

We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12,950 hrs of data (18.6 PB) accumulated over 10.5 years. The images were produced through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions. In our 120-168 MHz continuum mosaic images with an angular resolution of 6 arcsec (9 arcsec below declination 10$^\circ$) we catalogue 13,667,877 sources, formed from 16,943,656 Gaussian components. The scatter in the astrometric precision approximately follows the expected noise-like behaviour but with an additional systematic component of at least 0.24 arcsec that is likely due to calibration imperfections. The random flux density scale error is 6%, while the systematic offset was previously shown to be within 2%. The median sensitivity of our mosaics is 92$\mu$Jy beam$^{-1}$. Completeness simulations, accounting for realistic source models, time- and bandwidth-smearing effects, and astrometric errors, indicate that we detect more than 95% of compact sources with integrated flux densities exceeding 9 times the local root mean square (RMS) noise. However, the recovered source counts in a particular integrated flux density bin do not match the injected counts until flux densities exceed 45 times the local RMS noise. The Euclidean-normalised differential source counts derived from the survey constrain the radio source population over five orders of magnitude and are in good agreement with previous deep and wide-area surveys. All data products are publicly available, including catalogues, individual-field Stokes I, Q, U, and V images, mosaicked Stokes I images, and $uv$ data with associated direction-dependent calibration solutions.

astro-ph.GA↗

arXiv2026

CHANG-ES XXXVII. Effects of spectral aging on radio scale heights

Context. Cosmic rays and magnetic fields play an important role for the formation and evolution of galaxies. Radio continuum observations allows us to study them in the haloes of edge-on galaxies. Aims. We explore the frequency dependence of the radio scale height which depends on cosmic ray transport and electron cooling. We test the influence of fundamental galaxy properties, such as star-formation rate (SFR), mass and size. Methods. We used radio continuum data of 16 edge-on galaxies from the Continuum HAloes in Nearby Galaxies -- an EVLA Survey (CHANG-ES). We included maps from the LOw Frequency ARray at 144 MHz and from the Jansky Very Large Array at 3 GHz with 7" angular resolution. We extracted vertical intensity profiles within the effective radio radius and fitted beam-convolved double-exponential models to separate thin and thick discs. For the thick radio discs, we computed mean spectral indices and scale-height ratios between 144 MHz and 3 GHz. Results. We find a mean scale-height ratio of 1.26 \pm 0.16. This is much lower than what we would expect for either cosmic ray diffusion or advection if synchrotron and inverse Compton losses dominate for the electrons. There is a moderate positive correlation between the ratio and spectral index of the thick disc: galaxies with high ratios have flat radio spectra. The ratio does not depend on any other galaxy parameter. The radio spectrum of the thick disc, as indicated by the radio spectral index, steepens with total mass (strong correlation) and flattens with SFR-to-mass surface density (moderate correlation). Conclusions. Galaxies with galactic winds have flat radio continuum spectra and large scale heights at low frequencies. This shows effective transport of cosmic rays in such systems.

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.

astro-ph.GA↗

arXiv2025

CHANG-ES: XXXVI. The thin and thick radio discs

Context. Edge-on spiral galaxies give us an outsiders' view of the radio halo, which envelops these galaxies. The radio halos are caused by extra-planar cosmic-ray electrons that emit synchrotron emission in magnetic fields. Aims. We aim to study the origin of radio halos around galaxies and infer the role of cosmic-rays in supporting the gaseous discs. We would like to test the influence of star formation as the main source of cosmic rays as well as other fundamental galaxy properties such as mass and size. Methods. We present a study of radio continuum scale heights in 22 nearby edge-on galaxies from the CHANG-ES survey. We employ deep observations with the Jansky Very Large Array in the S-band (2-4 GHz), imaging at 7" angular resolution. We measure scale heights in three strips within the effective radio continuum radius, correcting for the influence of angular resolution and inclination angle. We include only galaxies where a distinction between the two disc components can be made in at least one of the strips, providing us with robust measurements of both scale heights. Results. We find a strong positive correlation between scale heights of the thin and thick discs and star-forming radius as well as star-formation rate (SFR); moderately strong correlations are found for the mass surface density and the ratio of SFR-to-mass surface density; no correlation is found with SFR surface density alone. Yet the SFR surface density plays a role as well: galaxies with high SFR surface densities have a rather roundish shape, whereas galaxies with little star formation show only a relatively small vertical extent in comparison to their size. Conclusions. Thick gaseous discs are partially supported by cosmic-ray pressure. Our results are a useful benchmark for simulations of galaxy evolution that include cosmic rays.

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arXiv2025

CHANG-ES XXXIV: Magnetic Field Structure in Edge-On Galaxies Characterising large-scale magnetic fields in galactic halos

Understanding galactic magnetic fields is essential for interpreting feedback processes in galaxies. Despite their importance, the exact structure of these fields, particularly in galactic halos, remains unclear. Accurate descriptions are crucial for understanding the interaction between star formation and halo magnetisation. By systematically analysing the polarisation patterns in halos of nearby galaxies, we aim to deepen the understanding of the interplay between galactic magnetic fields and star formation processes. We provide an analytical description of the observed X-shaped halos. Based on radio polarimetry data, we classify the polarisation patterns of a sample of edge-on galaxies, by using a newly introduced three-class system: disc dominated, small-scale, and X-shaped. We then fit X-shaped patterns to the polarisation data for galaxies classified as X-shaped and explore links between the polarisation patterns and other physical properties of these galaxies. The classification process shows that 11 out of 18 analysed galaxies display an X-shaped polarisation pattern. Galaxies classified as disc dominated seem less efficient at forming stars than expected for their stellar mass and rotate faster than galaxies with similarly sized HI-discs. X-shape modelling reveals that the polarisation patterns are best fitted by a constant-angle model, and we observe a correlation between the X-shape opening angle and star formation rate surface density indicating the interplay between the star formation in the disc and the magnetisation of the galactic halo. The analysis of polarisation patterns in nearby galaxies reveals that most exhibit an X-shaped configuration, indicating a common magnetic field structure in galactic halos. The introduced models capture the X-shaped morphology and reveal the link between the X-shape's opening angle and star formation rate surface density.

astro-ph.GA↗

arXiv2025

The low-frequency flattening of the radio spectrum of giant HII regions in M 101

In galaxies, the flattening of the spectrum at low radio frequencies below 300 MHz has been the subject of some debate. A turnover at low frequencies could be caused by multiple physical processes, which can yield new insights into the properties of the ionised gas in the interstellar medium. We investigate the existence and nature of the low-frequency turnover in the HII regions of M 101. We study the nearby galaxy M 101 using the LOw Frequency ARray (LOFAR) at frequencies of 54 and 144 MHz, Apertif at 1370 MHz, and published combined map from the Very Large Array (VLA) and Effelesberg telescope at 4850 MHz. The spectral index between 54 and 144 MHz is inverted at the centres of HII regions. We find a significant low-frequency flattening at the centres of five out of six HII regions that we selected for this study. The low frequency flattening in HII regions of M 101 can be explained with two different free-free absorption models. The flattening is localised in a region smaller than 1.5 kpc and can only be detected with high resolution (better than 45''). The detection of low frequency flattening has important consequences for using radio continuum observations below 100 MHz to measure extinction-free star-formation rates.

astro-ph.GA↗

arXiv2024

The ViCTORIA project: description of a multi-frequency radio survey of the Virgo galaxy cluster

The Virgo cluster is the closest richest nearby galaxy cluster. It is in the formation process, with a number of sub-clusters undergoing merging and interactions. Although a great laboratory to study galaxy evolution and cluster formation, its large apparent size and the severe dynamic range limitations due to the presence of the bright radio source Virgo A (M 87) reduced the ability of past wide-area radio surveys to image the region with high sensitivity and fidelity. In this paper we describe the "Virgo Cluster multi-Telescope Observations in Radio of Interacting galaxies and AGN" (ViCTORIA) project. The survey and its data reduction strategy are designed to mitigate the challenges of this field and deliver: images from 42 MHz to 1.7 GHz frequencies of the Virgo cluster, about 60 times deeper than existing data, in full polarisation, and including a blind HI survey that aims at mapping seven times more galaxies than previous experiments and without selection biases. Data have been collected with the Low-Frequency Array (LOFAR) and with MeerKAT in L-band, including polarisation and enough frequency resolution to conduct local HI studies. At the distance of Virgo, current radio instruments have the resolution to probe scales of ~500 pc and the sensitivity to study dwarf galaxies, the most fragile systems given their shallow gravitational potential wells, making Virgo a unique laboratory to study galaxy evolution and AGN feedback in a rich environment. In this work, we present some preliminary results, including high resolution images of the radio emission surrounding M 87, that show that the lobes are filled with filamentary structures. The combination of the presented radio surveys with state-of-the-art optical, UV, X-ray surveys will massively increase the scientific output from the studies of the Virgo cluster, making the ViCTORIA Project's legacy value outstanding.

astro-ph.CO↗

arXiv2024

Radio-FIR correlation- A probe into cosmic ray propagation in the nearby galaxy IC 342

Resolved studies of the correlation between the radio and far-infrared (FIR) emission from galaxies at different frequencies can unveil the interplay between star formation and relativistic interstellar medium (ISM). Thanks to the LOFAR LoTSS observations combined with the VLA, Herschel, and WISE data, we study the role of the cosmic rays and magnetic fields in the radio-FIR correlation on scales of ~> 200 pc in the nearby galaxy IC342. The thermal emission traced by the 22 micron emission, constitutes about 6%, 13%, and 30% of the observed radio emission at 0.14, 1.4, 4.8 GHz, respectively, in star forming regions and less in other parts. The nonthermal spectral index becomes flatter at frequencies lower than 1.4 GHz (a=-0.51 +- 0.09, S(nu)~ nu^(a)) than between 1.4 and 4.8 GHz (a = -1.06+- 0.19) on average and this flattening occurs not only in star-forming regions but also in diffuse ISM. The radio-FIR correlation holds at all radio frequencies; however, it is tighter at higher radio frequencies. A multi-scale analysis shows that this correlation cannot be maintained on small scales due to diffusion of cosmic ray electrons (CREs). The correlation breaks on a larger scale (320 pc) at 0.14 GHz than at 1.4 GHz (200 pc) indicating that those CREs traced at lower frequencies have diffused a longer path in the ISM. We find that the energy index of CREs becomes flatter in star forming regions in agreement with previous studies. Cooling of CREs due to the magnetic field is evident globally only after compensating for the effect of star formation activity which both accelerate CREs and amplify magnetic fields. Compared with other nearby galaxies, it is shown that the smallest scale of the radio-FIR correlation is proportional to the CREs propagation length on which the ordered magnetic field has an important effect.

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↗

arXiv2024

A spatially resolved radio spectral study of the galaxy M 51

Radio continuum emission from galaxies at gigahertz frequencies can be used as an extinction-free tracer of star formation. However, at frequencies of a few hundred megahertz, there is evidence for low-frequency spectral flattening. We wish to better understand the origin of this low-frequency flattening and, to this end, perform a spatially resolved study of the nearby spiral galaxy M 51. We explore the different effects that can cause flattening of the spectrum towards lower frequencies, such as free-free absorption and cosmic-ray ionisation losses. We used radio continuum intensity maps between 54 and 8350 MHz at eight different frequencies, with observations at 240 MHz from the Giant Metrewave Radio Telescope presented for the first time. We corrected for contribution from thermal free-free emission using an H$\alpha$ map that has been extinction-corrected with 24 $\mu$m data. We fitted free-free absorption models to the radio spectra to determine the emission measure (EM) as well as polynomial functions to measure the non-thermal spectral curvature. The non-thermal low-frequency radio continuum spectrum between 54 and 144 MHz is very flat and even partially inverted, particularly in the spiral arms; contrary, the spectrum at higher frequencies shows the typical non-thermal radio continuum spectrum. However, we do not find any correlation between the EMs calculated from radio and from H$\alpha$ observations; instead, the non-thermal spectral curvature weakly correlates with the HI gas mass surface density. This suggests that cosmic-ray ionisation losses play an important role in the low-frequency spectral flattening. The observed spectral flattening towards low frequencies in M 51 is caused by a combination of ionisation losses and free-free absorption. The reasons for this flattening need to be understood in order to use sub-GHz frequencies as a star-formation tracer.

astro-ph.GA↗

arXiv2024

ViCTORIA project: The LOFAR-MeerKAT view of AGN in Virgo cluster early-type galaxies

The evolution of Active Galactic Nuclei (AGN) is closely connected to their host galaxies and surroundings. Via feedback processes, AGN can counteract the cooling of the intracluster medium (ICM) and suppress star formation in their host galaxies. Radio observations at low frequencies provide a glimpse into the history of AGN activity. The Virgo cluster is a substantial reservoir of nearby galaxies and provides an ideal laboratory for the study of AGN as well as their feedback mechanisms. The aim of our work is to characterise the AGN population within the Virgo cluster down to low radio luminosities, constrain the AGN duty cycle and investigate environmental feedback in cluster member galaxies. We analyse 144 MHz and 1.3 GHz radio observations of early-type galaxies from the ACS Virgo Cluster Survey (ACSVCS) taken with LOFAR and MeerKAT. We detect 12 of these galaxies at 144 MHz, 5 of which show clearly extended radio emission. The radio luminosity shows a strong dependence on the stellar mass of the host galaxy, in agreement with previous results. As a notable outlier, the massive elliptical galaxy NGC 4365 ($M_* = 2.2 \times 10^{11} M_\odot$) is not detected as a compact source in the LOFAR observations. Instead, it is surrounded by diffuse, low-surface brightness emission, which hints towards a past phase of stronger nuclear activity. Furthermore, we find a cavity in NGC 4472 (= M 49) inflated by the wide-angle tail only visible in the LOFAR data, which implies that the cavity was created by a past outburst. The corresponding cavity power is of the same order of magnitude as the jet power in the present duty cycle of the AGN.

astro-ph.HE↗

arXiv2023

ViCTORIA project: The LOFAR-view of environmental effects in Virgo Cluster star-forming galaxies

Environmental effects such as ram-pressure stripping (RPS) shape the evolution of galaxies in dense regions. We use the nearby Virgo cluster as a laboratory to study environmental effects on the non-thermal components of star-forming galaxies. We constructed a sample of 17 RPS galaxies in the Virgo cluster and a statistical control sample of 119 nearby galaxies from the Herschel Reference Survey. All objects in these samples are detected in LOFAR 144 MHz observations and come with H$\alpha$ and/or far-UV star formation rate (SFR) estimates. We derived the radio-SFR relations, confirming a clearly super-linear slope of $\approx1.4$. We found that Virgo cluster RPS galaxies have radio luminosities that are a factor of 2-3 larger than galaxies in our control sample. We also investigated the total mass-spectral index relation, where we found a relation for the Virgo cluster RPS galaxies that is shifted to steeper spectral index values by $0.17\pm0.06$. Analyzing the spatially resolved ratio between the observed and the expected radio emission based on the hybrid near-UV + 100$\,\mu$m SFR surface density, we generally observe excess radio emission all across the disk with the exception of a few leading-edge radio-deficient regions. The radio excess and the spectral steepening for the RPS sample could be explained by an increased magnetic field strength if the disk-wide radio enhancement is due to projection effects. For the galaxies that show the strongest radio excesses (NGC 4330, NGC 4396, NGC 4522), a rapid decline of the SFR ($t_\mathrm{quench} \leq 100$ Myr) could be an alternative explanation. We disfavor shock acceleration of electrons as cause for the radio excess since it cannot easily explain the spectral steepening and radio morphology.

astro-ph.GA↗

arXiv2023

Nearby galaxies in the LOFAR Two-metre Sky Survey III. Influence of cosmic-ray transport on the radio-SFR relation

Context. In order to understand galaxy evolution, it is essential to measure star formation rates (SFRs) across Cosmic times. Aims. The use of radio continuum emission as an extinction-free star formation tracer necessitates a good understanding of the influence of cosmic-ray electron (CRE) transport that we are aiming to improve with this work. Methods. We analyse the spatially resolved radio continuum-star-formation rate (radio-SFR) relation in 15 nearby galaxies using data from the LOw Frequency ARray (LOFAR) and the Westerbork Synthesis Radio Telescope (WSRT) at 144 and 1365 MHz, respectively. The hybrid SFR maps are based on observations with Spitzer at 24 $ {\mu}$m and with GALEX at 156 nm. Our pixel-by-pixel analysis at 1.2 kpc resolution reveals the usual sublinear radio-SFR relation for local measurements which can be linearised with a smoothing experiment, convolving the hybrid SFR map with a Gaussian kernel that provides us with the CRE transport length. Results. CRE transport can be described as energy-independent isotropic diffusion. If we consider only young CREs as identified with the radio spectral index, we find a linear relation showing the influence of cosmic-ray transport. We then define the CRE calorimetric efficiency as the ratio of radio-to-hybrid SFR surface density and show that it is a function of the radio spectral index. If we correct the radio-SFR relation for the CRE calorimetric efficiency parametrised with the radio spectral index, it becomes nearly linear with a slope of $1.01\pm 0.02$ independent of frequency. Conclusions. The corrected radio-SFR relation is universal and holds, both, for global and local measurements.

astro-ph.GA↗

arXiv2023

Metal-THINGS: a panchromatic analysis of the local scaling relationships of the dwarf irregular galaxy NGC 1569

We investigate several panchromatic scaling relations (SRs) for the dwarf irregular galaxy NGC 1569 using IFU data from the Metal-THINGS Survey. Among the spatially resolved properties analyzed, we explore SRs between the stellar mass, SFR, molecular gas, total gas, baryonic mass, gas metallicity, gas fraction, SFE and effective oxygen yields. Such multiwavelength SRs are analyzed at a spatial resolution of 180 pc, by combining our IFU observations with data from the surveys THINGS, CARMA, and archival data from DustPedia. Although we recover several known relations, our slopes are different to previously reported ones. Our star formation main sequence, Kennicutt-Schmidt (KS) and molecular KS relations show higher SFRs, lower scatter, and higher correlations, with steeper (1.21), and flatter slopes (0.96, 0.58) respectively. The shape of the SRs including metallicity, stellar mass, and gas fraction are flat, with an average value of 12+log(O/H) $\sim$ 8.12 dex. The baryonic mass vs effective oxygen yields, and the stellar, gas and baryonic mass vs SFE show higher dispersions and lower correlations. Since we use the dust mass as a tracer of gas mass, we derive the Dust-to-Gas Ratio and the CO luminosity-to-molecular gas mass conversion factors, showing differences of 0.16 and 0.95 dex for the total and molecular gas surface density, respectively, in comparison to previously reported values. We use a self regulated feedback model to conclude that stellar feedback plays an important role generating outflows in NGC 1569.

astro-ph.GA↗

arXiv2023

Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE

The detection and study of magnetic fields surrounding galaxies is important to understand galaxy evolution since magnetic fields are tracers for dynamical processes in the circumgalactic medium (CGM) and can have a significant impact on the evolution of the CGM. The Faraday rotation measure (RM) of the polarized light of background radio sources passing through the magnetized CGM of intervening galaxies can be used as a tracer for the strength and extent of magnetic fields around galaxies. We use rotation measures observed by the MIGHTEE-POL (MeerKAT International GHz Tiered Extragalactic Exploration POLarisation) survey by MeerKAT in the XMM-LSS and COSMOS fields to investigate the RM around foreground star-forming galaxies. We use spectroscopic catalogs of star-forming and blue cloud galaxies to measure the RM of MIGHTEE-POL sources as a function of the impact parameter from the intervening galaxy. We then repeat this procedure using a deeper galaxy catalog with photometric redshifts. For the spectroscopic star-forming sample we find a redshift-corrected |RM| excess of 5.6 +/- 2.3 rad m-2 which corresponds to a 2.5 sigma significance around galaxies with a median redshift of z = 0.46 for impact parameters below 130 kpc only selecting the intervenor with the smallest impact parameter. Making use of a photometric galaxy catalog and taking into account all intervenors with Mg < -13.6 mag, the signal disappears. We find no indication for a correlation between redshift and RM, nor do we find a connection between the total number of intervenors to the total |RM| . We have presented tentative evidence that the CGM of star-forming galaxies is permeated by coherent magnetic fields within the virial radius. We conclude that mostly bright, star-forming galaxies with impact parameters less than 130 kpc significantly contribute to the RM of the background radio source.

astro-ph.GA↗