Gamma-Ray Emission from Arp 220: Indications of an Active Galactic Nucleus

Extragalactic cosmic ray populations are important diagnostic tools for tracking the distribution of energy in nuclei and for distinguishing between activity powered by star formation versus active galactic nuclei (AGNs). Here, we compare different diagnostics of the cosmic ray populations of the nuclei of Arp 220 based on radio synchrotron observations and the recent gamma-ray detection. We find the gamma-ray and radio emission to be incompatible; a joint solution requires at minimum a factor of 4 - 8 times more energy coming from supernovae and a factor of 40 - 70 more mass in molecular gas than is observed. We conclude that this excess of gamma-ray flux in comparison to all other diagnostics of star-forming activity indicates that there is an AGN present that is providing the extra cosmic rays, likely in the western nucleus.Comment: 5 pages, 3 figures, 1 table, accepted for publication in MNRAS Letter

A search for radio emission from exoplanets around evolved stars

The majority of searches for radio emission from exoplanets have to date focused on short period planets, i.e., the so-called hot Jupiter type planets. However, these planets are likely to be tidally locked to their host stars and may not generate sufficiently strong magnetic fields to emit electron cyclotron maser emission at the low frequencies used in observations (typically >150 MHz). In comparison, the large mass-loss rates of evolved stars could enable exoplanets at larger orbital distances to emit detectable radio emission. Here, we first show that the large ionized mass-loss rates of certain evolved stars relative to the solar value could make them detectable with the Low Frequency Array (LOFAR) at 150 MHz ($\lambda$ = 2 m), provided they have surface magnetic field strengths >50 G. We then report radio observations of three long period (>1 au) planets that orbit the evolved stars $\beta$ Gem, $\iota$ Dra, and $\beta$ UMi using LOFAR at 150 MHz. We do not detect radio emission from any system but place tight 3$\sigma$ upper limits of 0.98, 0.87, and 0.57 mJy on the flux density at 150 MHz for $\beta$ Gem, $\iota$ Dra, and $\beta$ UMi, respectively. Despite our non-detections these stringent upper limits highlight the potential of LOFAR as a tool to search for exoplanetary radio emission at meter wavelengths.Comment: 9 pages, 3 figure

Interactions between fungi, forest management, and ecosystem services

Fungi provide a wide range of ecosystem services (ES) in forests but have for long been difficult to study. Knowledge of their role in soil processes has therefore been lacking and not accounted for in forest management. With the recent development in methodology, we have begun to learn more about fungi and their role in ES provisioning. Interactions between fungi, forest management, and ES were investigated in boreal forests in Sweden. Soil fungal communities were characterised using high-throughput sequencing. Long-term impacts of tree harvesting versus retaining trees on the composition of ectomycorrhizal fungal (EMF) communities were investigated. Furthermore, as part of the Swedish Forest Soil Inventory and National Forest Inventory, and using structural equation modelling, the interplay between soil fungal community composition and tree growth was investigated. Finally, ES provided by fungi in forests were reviewed and potential consequences of Swedish forest management on selected ES were discussed. Temporary retention of trees for ten years did not seem to compensate for harvesting induced changes in EMF communities, which seemingly lasted for several decades. Permanent retention trees enabled local maintenance of some EMF. These results indicate that harvesting induced soil chemistry changes are more important than tree continuity in deciding post-harvest composition of EMF communities. Therefore, if aiming to conserve EMF, it is recommended to retain intact forest patches. Soil fungal community composition seemed to correlate with tree growth. Increased knowledge on fungal functional traits may therefore improve predictions of boreal forest productivity. Intensive management may alter fungal communities leading to undesired consequences for ES provided by fungi. A proposed way to ensure resilience of managed forests is therefore to consider potential impacts of forestry on fungal communities and to simultaneously aim for multiple ES

Investigating the origin of radio emission in nearby starburst galaxies via high-resolution metre and centimetre observations

Star formation and galaxy evolution are intimately linked together. A detailed understanding of the physics of star formation can help us explain how galaxies evolve into, for example, our present Milky Way. Using Very Long Baseline Interferometry (VLBI) techniques it is possible to achieve high enough angular resolution to study radio emission from other galaxies in great detail. This thesis presents observations of three nearby Luminous Infrared Galaxies (LIRGs): NGC 4418, M 82 and Arp 220. While the centres of these galaxies are all heavily obscured in optical wavelengths, radio observations can be used to probe star formation properties in the centres of these galaxies.<br />The galaxy NGC 4418 is radio weak with respect to the far infrared (FIR)-radio correlation for star forming galaxies. We present evidence for a young starburst in the centre, likely fuelled by gas falling in from a recent interaction with the nearby galaxy VV 655. We argue that this scenario can explain the low radio luminosity of this galaxy, and possibly also of other galaxies which appear to be radio weak.<br />M 82 and Arp 220 follow the FIR-radio correlation and are excellent laboratories to study the physics of star formation in extreme environments. In this thesis we report on new groundbreaking subarcsecond resolution observations of M 82 and Arp 220 with the international LOFAR telescope, where we for the first time spatially resolve the radio emission from their nuclei at metre wavelengths. We report on previously unknown steep-spectrum radio structures and study effects of free-free absorption. We conclude that high angular resolution is essential for a correct interpretation of the radio emission from these complex objects. Furthermore, this work demonstrates that LOFAR can be used to obtain subarcsecond resolution images at metre wavelengths, a capability which can be used in multiple areas of astronomy in the future.<br />Finally, we present results from new and archival global VLBI observations of Arp 220 spanning 17 years. We show that a self-consistent approach is essential to understand the nature of the radio emission. We find the data rich in details: we detect more than 80 compact objects, many with luminosities and sizes measured at multiple times and frequencies. We present a first analysis of the data where we discuss the general properties of the source population

The Current and Future Performance of VGOS

In this work we investigate the performance\ua0of the 24-hour VGOS sessions observed in 2019–2021.\ua0We look at the station positions and the Earth Orientation\ua0parameters (EOP), and we compare them with\ua0the results from the legacy S/X VLBI sessions as well\ua0as with simulations. We find that the station position\ua0repeatabilities obtained from the VGOS sessions are\ua0significantly better than what is obtained from the\ua0legacy S/X VLBI sessions. However, the EOP from the\ua0VGOS sessions are less accurate than those from the\ua0legacy S/X sessions, a consequence of the low number\ua0and poor global coverage of the currently operational\ua0VGOS stations

Short-baseline interferometry local-tie experiments at the Onsala Space Observatory

We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: nu Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10-15 ps using group-delays and 2-5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset similar to+3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset

Methanol masers reveal the magnetic field of the high-mass protostar IRAS 18089-1732

Context. The importance of the magnetic field in high-mass-star formation is not yet fully clear and there are still many open questions concerning its role in the accretion processes and generation of jets and outflows. In the past few years, masers have been successfully used to probe the magnetic field morphology and strength at scales of a few au around massive protostars, by measuring linear polarisation angles and Zeeman splitting. The massive protostar IRAS 18089-1732 is a well studied high-mass-star forming region, showing a hot core chemistry and a disc-outflow system. Previous SMA observations of polarised dust revealed an ordered magnetic field oriented around the disc of IRAS 18089-1732. Aims. We want to determine the magnetic field in the dense region probed by 6.7 GHz methanol maser observations and compare it with observations in dust continuum polarisation, to investigate how the magnetic field in the compact maser region relates to the large-scale field around massive protostars. Methods. We reduced MERLIN observations at 6.7 GHz of IRAS 18089-1732 and we analysed the polarised emission by methanol masers. Results. Our MERLIN observations show that the magnetic field in the 6.7 GHz methanol maser region is consistent with the magnetic field constrained by the SMA dust polarisation observations. A tentative detection of circularly polarised line emission is also presented. Conclusions. We found that the magnetic field in the maser region has the same orientation as in the disk. Thus the large-scale field component, even at the au scale of the masers, dominates over any small-scale field fluctuations. We obtained, from the circular polarisation tentative detection, a field strength along the line of sight of 5.5 mG which appeared to be consistent with the previous estimates.Comment: 12 pages, 7 figures, accepted for publication in A&

Obtaining Local-Tie Vectors from Short-Baseline Interferometry

With the VLBI Global Observing System (VGOS) being the next step in the development of geodetic VLBI, it is necessary to connect the new VGOS network to the existing legacy S/X telescopes. At the Onsala Space Observatory (OSO), this is being done by short-baseline interferometry between the VGOS Onsala twin telescopes ONSA13SW and ONSA13NE and the legacy antenna ONSALA60.The main aim of these sessions, referred to as ONTIE, is to obtain local-tie vectors between these three OSO telescopes that all take part in regular geodetic VLBI observations. Each ONTIE session is about 24 h long, during which all three telescopes observe simultaneously the same sources at X-band. A total of 37 ONTIE sessions have been observed since April 2019. In November 2021, the ONTIE sessions were for the first time observed with alternative observation frequency setups in order to mitigate the influence of known RFI. Additionally, scheduling was done — also for the first time — with VieSched++ instead of sked.Interesting findings of the ONTIE sessions include unexpected offsets in the results of group and phase delays, jumps in the coordinates of the twin telescopes, and apparent yearly trends that might be an artifact of unmodeled thermal expansion of the telescopes that is left in the data.Future ONTIE sessions are envisioned to happen on a regular basis and could, as a by-product, also serve as quasar flux-monitoring sessions by investigation of the recorded system temperatures during observation.This paper summarizes the current status and results of the ONTIE sessions

Observing UT1‑UTC with VGOS

We present first results for the determination of UT1-UTC using the VLBI Global Observing System (VGOS). During\ua0December 2019 through February 2020, a series of 1 h long observing sessions were performed using the VGOS stations\ua0at Ishioka in Japan and the Onsala twin telescopes in Sweden. These VGOS-B sessions were observed simultaneously\ua0to standard legacy S/X-band Intensive sessions. The VGOS-B data were correlated, post-correlation processed,\ua0and analysed at the Onsala Space Observatory. The derived UT1-UTC results were compared to corresponding results\ua0from standard legacy S/X-band Intensive sessions (INT1/INT2), as well as to the final values of the International Earth\ua0Rotation and Reference Frame Service (IERS), provided in IERS Bulletin B. The VGOS-B series achieves 3–4 times lower\ua0formal uncertainties for the UT1-UTC results than standard legacy S/X-band INT series. The RMS agreement w.r.t. to\ua0IERS Bulletin B is slightly better for the VGOS-B results than for the simultaneously observed legacy S/X-band INT1\ua0results, and the VGOS-B results have a small bias only with the smallest remaining standard deviation