MeerKAT

Abstract:

Context. It is crucial to know the polarization properties of coherent radio waves that escape from pulsar polar caps to calculate the radiative transfer through the magnetosphere and to predict observable radio properties. Aims. We describe pair cascades in the pulsar polar cap, and we determine for the first time the Stokes parameters of the escaping radio waves from first-principle kinetic simulations for a pulsar with a magnetic obliquity of 60°. Methods. We present 3D particle-in-cell kinetic simulations that include quantum-electrodynamic pair cascades in a charge-limited flow from the stellar surface. Results. Our model quantitatively and qualitatively explains the observed pulsar radio powers and spectra, the pulse profiles, polarization curves, their temporal variability, the strong Stokes- L and weak Stokes- V polarization components, the decline in the linear polarization with frequency, and the nonexistence of a radius-to-frequency relation. The observable properties of radio emission from the polar cap can vary and include single- or double-peaked profiles. Most of the Stokes V curves from our simulations appear to be antisymmetric, but symmetric curves are also present at some viewing angles. Although the polarization-angle (PA) swing of the radiation from the polar cap fits the rotating vector model (RVM) for most viewing angles, the angles obtained from the RVM do not correspond to the dipole geometry of the magnetic field. Instead, the PA is directly related to the plasma flows in the polar cap. Furthermore, we found that the radiation is associated with escaping plasma bunches and can propagate freely along channels of low plasma density, in addition to being reflected at the channel boundaries. Conclusions. Our simulations demonstrate that pair discharges close to the surface of the polar cap cause the radio emission of pulsars and determine the majority of their typically observed properties. The merits of RVM for estimations of the magnetic field geometry from observations need to be reevaluated.

Abstract:

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 h of data (18.6 PB) accumulated over 10.5 years. Producing the images took 20 million core hours of processing 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″ (9″ below declination 10°) 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″ 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 μJy beam −1 , improving to 68 μJy beam −1 at high observing elevations, but degrading to 183 μJy beam −1 at the celestial equator due to station area projection effects. 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.

Abstract:

Untargeted neutral hydrogen ( > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE detections to find 29 LSBGs, and 26 of these meet the size requirement (R_ eff spectra at the location of all optically identified galaxies, placing upper limits on the mass ratio in these systems. While the population overall tends toward bluer colors, the and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the LSBGs were missed in optical searches, this work highlights the utility of surveys in finding these faint systems. The LSBGs are gas rich compared to the general population. Furthermore, three out of four UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of observations for finding and characterizing the low surface brightness Universe.

Abstract:

As radio emission from normal galaxies is a dust-free tracer of star formation, tracing the star formation history of the Universe is a key goal of the Square Kilometre Array and the Next-Generation Very Large Array. In order to investigate how well radio luminosity traces star formation rate (SFR) in the early Universe, we have examined the radio properties of a JWST Paα sample of galaxies at 1.0 ≲ z ≲ 1.8. In the GOODS-S field, we cross-matched a sample of 506 FRESCO Paα emitters with the 1.23 GHz radio continuum data from the MeerKAT MIGHTEE survey, finding 47 detections. After filtering for active galactic nuclei (via X-ray detections, hot mid-infrared dust, and extended radio emission), as well as blended sources, we obtained a sample of star-forming galaxies comprising 11 cataloged radio detections, 18 noncataloged detections (at ≈3σ–5σ), and 298 undetected sources. Stacking the 298 undetected sources, we obtain a 3.3σ detection in the radio. This sample, along with a local sample of Paα emitters, lies along previous radio luminosity/SFR relations from local (<0.2) to high redshift (z ∼ 1). Fitting the FRESCO data at 1.0 ≲ z ≲ 1.8, we find log(L1.4GHz)= (1.31 ± 0.17) × log(SFRPaα)+ (21.36 ± 0.17), which is consistent with other literature relations. We can explain some of the observed scatter in the L1.4GHz/SFRPaα correlation by a toy model in which the synchrotron emission is a delayed/averaged tracer of the instantaneous Paα SFR by ∼10/75 Myr.

Abstract:

ABSTRACT We study the spatially resolved star formation, gas ionization, and outflow properties of 1813 active galactic nuclei (AGNs) from the MaNGA survey, which we classify into infrared (IR), broad-line (BL), narrow-line (NL), and radio (RD) AGNs based on their mid-infrared colours, optical spectra, and/or radio photometry. We also provide estimations of AGN power at different wavelengths. AGN incidence is found to increase with stellar mass following a power law, with the high-mass end dominated by RDAGNs and the low-mass end dominated by NLAGNs. Compared to their mass-matched non-AGN counterparts, we find that IRAGNs, BLAGNs, and NLAGNs on average show enhanced specific star formation rates, younger stellar populations, and harder ionization towards the centre. RDAGNs, in contrast, show radial profiles similar to quiescent galaxies. [O iii] outflows are more common and stronger in BL/IRAGNs, while RDAGNs on average show no outflow features. The outflow incidence increases with [O iii] luminosity, and the features in BL/IRAGNs on average extend to $\sim$2 kpc from the nuclei. We further discuss a possible evolutionary sequence of AGNs and their host galaxies, where AGNs with strong emission lines or dust tori are present in star-forming galaxies. Later, young compact radio jets emerge, the host galaxies gradually quench, and the AGN hosts eventually evolve into globally quiescent systems with larger radio jets that prevent further gas cooling.