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Much has been written about the representation of noisy linear 2-ports. Here we present a theory of noisy $N$-ports. We show how in the general case there are $(2N)!/(N!)^2$ equivalent representations and give the transformations relating them. We also discuss singular cases in which some of the transformations are not possible as well as how to measure the noise properties of an $N$-port. This work is motivated by the REACH experiment to observe the global 21 cm signal for which modelling noise with exquisite precision is essential for a reliable calibration., Comment: 5 pages Latex with IEEE macro package + 6 figures

We analyse a lossy transmission line and the Johnson-Nyquist noise generated therein. A representation as a noisy two-port with a voltage and a current noise sources on one end of a noiseless two-port is given. An expression for the noise properties is given for an arbitrary temperature profile along the transmission line. Agreement is demonstrated between the general expression found here and special cases calculable using thermodynamics. This work is motivated by the REACH experiment to observe the global 21 cm signal for which modelling noise with exquisite precision is essential for a reliable calibration., Comment: 6 pages Latex with IEEE macro package + 4 figures

Analog tunable memristors are widely utilized as artificial synapses in various neural network applications. However, exploiting the dynamical aspects of their conductance change to implement active neurons is still in its infancy, awaiting the realization of efficient neural signal recognition functionalities. Here we experimentally demonstrate an artificial neural information processing unit that can detect a temporal pattern in a very noisy environment, fire a single output spike upon successful detection and reset itself in a fully unsupervised, autonomous manner. This circuit relies on the dynamical operation of only two memristive blocks: a non-volatile Ta$_2$O$_5$ device and a volatile VO$_2$ unit. A fading functionality with exponentially tunable memory time constant enables adaptive operation dynamics, which can be tailored for the targeted temporal pattern recognition task. In the trained circuit false input patterns only induce short-term variations. In contrast, the desired signal activates long-term memory operation of the non-volatile component, which triggers a firing output of the volatile block., Comment: 11 pages, 6 figures

We study the evolutionary path of the Fornax cluster galaxy NGC$~$1436, which is known to be currently transitioning from a spiral into a lenticular morphology. This galaxy hosts an inner star-forming disc and an outer quiescent disc, and we analyse data from the MeerKAT Fornax Survey, ALMA, and the Fornax3D survey to study the interstellar medium and the stellar populations of both disc components. Thanks to the combination of high resolution and sensitivity of the MeerKAT data, we find that the $\textrm{H}\scriptstyle\mathrm{I}$ is entirely confined within the inner star-forming disc, and that its kinematics is coincident with that of the CO. The cold gas disc is now well settled, which suggests that the galaxy has not been affected by any environmental interactions in the last $\sim1~$Gyr. The star formation history derived from the Fornax3D data shows that both the inner and outer disc experienced a burst of star formation $\sim5$ Gyr ago, followed by rapid quenching in the outer disc and by slow quenching in the inner disc, which continues forming stars to this day. We claim that NGC$~$1436 has begun to effectively interact with the cluster environment 5$~$Gyr ago, when a combination of gravitational and hydrodynamical interactions caused the temporary enhancement of the star-formation rate. Furthermore, due to the weaker gravitational binding $\textrm{H}\scriptstyle\mathrm{I}$ was stripped from the outer disc, causing its rapid quenching. At the same time, accretion of gas onto the inner disc stopped, causing slow quenching in this region., Comment: Monthly Notices of the Royal Astronomical Society (MNRAS), accepted for publication. Data available at the MeerKAT Fornax Survey website https://sites.google.com/inaf.it/meerkatfornaxsurvey

Observations of the neutral atomic hydrogen (HI) in the nuclear starburst galaxy NGC 4945 with MeerKAT are presented. We find a large amount of halo gas, previously missed by HI observations, accounting for 6.8% of the total HI mass. This is most likely gas blown into the halo by star formation. Our maps go down to a $3\sigma$ column density level of $5\times10^{18} cm^{-2}$ . We model the HI distribution using tilted-ring fitting techniques and find a warp on the galaxy's approaching and receding sides. The HI in the northern side of the galaxy appears to be suppressed. This may be the result of ionisation by the starburst activity in the galaxy, as suggested by a previous study. The origin of the warp is unclear but could be due to past interactions or ram pressure stripping. Broad, asymmetric HI absorption lines extending beyond the HI emission velocity channels are present towards the nuclear region of NGC 4945. Such broad lines suggest the existence of a nuclear ring moving at a high circular velocity. This is supported by the clear rotation patterns in the HI absorption velocity field. The asymmetry of the absorption spectra can be caused by outflows or inflows of gas in the nuclear region of NGC 4945. The continuum map shows small extensions on both sides of the galaxy's major axis that might be signs of outflows resulting from the starburst activity., Comment: 20 pages, 15 figures, 3 tables, accepted for publication in MNRAS

We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (\HI) around the core triplet galaxies in the nearby NGC~7232 galaxy group with MeerKAT. With a physical resolution of $\sim$1 kpc, we detect a complex web of low surface brightness \HI\ emission down to a 4$\sigma$ column density level of $\sim$1 $\times$ 10$^{19}$ cm$^{-2}$ (over 44 \kms ). The newly discovered H\,{\sc i} streams extend over $\sim$20 arcmin corresponding to 140~kpc in projection. This is $\sim$3 times the \HI\ extent of the galaxy triplet (52 kpc). The \HI\ debris has an \HI\ mass of $\sim$6.6 $\times 10^9$~M$_{\odot}$, more than 50\% of the total \HI\ mass of the triplet. Within the galaxy triplet, NGC~7233 and NGC~7232 have lost a significant amount of \HI\ while NGC~7232B appears to have an excess of \HI. The \HI\ deficiency in NGC~7232 and NGC~7233 indicates that galaxy-galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies we find that with regards to its total \HI\ mass the NGC~7232/3 galaxy triplet is not \HI\ deficient. Despite the many interactions associated to the triplet galaxies, no \HI\ seems to have been lost from the group (yet)., Comment: 17 pages, 11 figures, accepted for publication in MNRAS

Examining cables using many conductor transmission line theory has shed light on the modes supported by various cable types. However, so far the theory disregards the fundamental surface wave mode whose lateral confinement increases with frequency and hence is expected to play an important role in high frequency applications. To address this issue, we propose an extension to the theory which incorporates surface waves on uncoated, cylindrical wires. Crucially, this requires new definitions of the per unit length transmission line parameters which are derived using the single wire surface wave solution. By closely examining a two wire and three wire system, we show that these new parameters can predict surface waves as well as modes found using conventional many conductor transmission line theory. Furthermore, all calculated modes are validated experimentally by diagonalization of a measured channel transfer matrix. Additionally, the theoretically predicted propagation constants for the modes are validated against full numerical simulation for the two wire case and good agreement is observed when proximity effects can be neglected., Comment: 22 pages, 5 Figures, data and supplementary material will be made available at a later stage

The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity-star formation rate (SFR) calibrations. In preparation for the new generation of radio surveys we revisit the IRRC of low-$z$ galaxies by (a) drawing on the best currently available IR and 1.4 GHz radio photometry, plus ancillary data over the widest possible area, and (b) carefully assessing potential systematics. We compile a catalogue of $\sim$9,500 z $<$ 0.2 galaxies and derive their 1.4 GHz radio ($L_{\mathrm{1.4}}$), total IR, and monochromatic IR luminosities in up to seven bands, allowing us to parameterize the wavelength-dependence of monochromatic IRRCs from 22-500 $\mu$m. For the first time for low-$z$ samples, we quantify how poorly matched IR and radio survey depths bias measured median IR/radio ratios, $\overline{q}_{\mathrm{TIR}}$, and discuss the level of biasing expected for low-z IRRC studies in ASKAP/MeerKAT fields. For our subset of $\sim$2,000 high-confidence star-forming galaxies we find a median $\overline{q}_{\mathrm{TIR}}$ of 2.54 (scatter: 0.17 dex). We show that $\overline{q}_{\mathrm{TIR}}$ correlates with $L_{\mathrm{1.4}}$, implying a non-linear IRRC with slope 1.11$\pm$0.01. Our new $L_{\mathrm{1.4}}$-SFR calibration, which incorporates this non-linearity, reproduces SFRs from panchromatic SED fits substantially better than previous IRRC-based recipes. Finally, we match the evolutionary slope of recently measured $\overline{q}_{\mathrm{TIR}}$-redshift trends without having to invoke redshift evolution of the IRRC. In this framework, the redshift evolution of $\overline{q}_{\mathrm{TIR}}$ reported at GHz frequencies in the literature is the consequence of a partial, redshift-dependent sampling of a non-linear IRRC obeyed by low-$z$ {\it and} distant galaxies., Comment: Accepted for publication in MNRAS. 29 pages, 20 figures, 9 tables including appendices

ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (HI) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar HI component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy's morphology, which shows a high degree of asymmetry. By comparing our model with the observed HI, we find that in our model we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube we estimate that at least 7%-8% of the HI in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1% for the morphologically confirmed extraplanar component. We investigate a number of global scaling relations and find that, besides being gas-dominated with a neutral gas-to-stellar mass ratio of 1.7, the galaxy does not show any obvious global peculiarities. Given its isolation, as confirmed by optical observations, we conclude that the galaxy is likely currently acquiring neutral gas. It is either re-accreting gas expelled from the galaxy or accreting pristine intergalactic material., Comment: 16 pages, 14 figures, MNRAS, Accepted 2020 December 2, in original form 2019 September 18

This paper analyses the surface wave mode propagating along a simplified planar Goubau line consisting of a perfectly conducting circular wire on top of a dielectric substrate of finite thickness but infinite width. An approximate equation for the propagation constant is derived and solved through numerical integration. The dependence of the propagation constant on various system parameters is calculated and the results agree well with full numerical simulations. In addition, the spatial distribution of the longitudinal electric field is reported and excellent agreement with the numerical simulation and previous studies is found. Moreover, validation against experimental phase velocity measurements is also reported. Finally, insights gained from the model are considered for a Goubau line with a rectangular conductor. These results present the first step towards an analytic model of the planar Goubau line., Comment: 15 pages, 4 figures Submitted To Nature Scientific Reports

We present observations and models of the kinematics and the distribution of the neutral hydrogen (HI) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The HI disc of WLM extends out to a major axis diameter of 30 arcmin (8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the TiRiFiC software suite, allowing us to fit different tilted-ring models and select the one that best matches the observation. Our final best-fitting model is a flat disc with a vertical thickness, a constant inclination and dispersion, and a radially-varying surface brightness with harmonic distortions. To simulate bar-like motions, we include second-order harmonic distortions in velocity in the tangential and the vertical directions. We present a model with only circular motions included and a model with non-circular motions. The latter describes the data better. Overall, the models reproduce the global distribution and the kinematics of the gas, except for some faint emission at the 2-sigma level. We model the mass distribution of WLM with a pseudo-isothermal (ISO) and a Navarro-Frenk-White (NFW) dark matter halo models. The NFW and the ISO models fit the derived rotation curves within the formal errors, but with the ISO model giving better reduced chi-square values. The mass distribution in WLM is dominated by dark matter at all radii., Comment: Accepted for publication in MNRAS, 25 pages, 21 figures, 5 tables

MeerKATHI is the current development name for a radio-interferometric data reduction pipeline, assembled by an international collaboration. We create a publicly available end-to-end continuum- and line imaging pipeline for MeerKAT and other radio telescopes. We implement advanced techniques that are suitable for producing high-dynamic-range continuum images and spectroscopic data cubes. Using containerization, our pipeline is platform-independent. Furthermore, we are applying a standardized approach for using a number of different of advanced software suites, partly developed within our group. We aim to use distributed computing approaches throughout our pipeline to enable the user to reduce larger data sets like those provided by radio telescopes such as MeerKAT. The pipeline also delivers a set of imaging quality metrics that give the user the opportunity to efficiently assess the data quality., Comment: 4 pages, 1 figure, in conference proceedings of the ADASS XXIX, to appear in ASPC. CARACal (formerly MeerKATHI) can be accessed at: https://caracal.readthedocs.io

In this work, we provide a simultaneous and accurate description of the $\pi^+\pi^-$ and $\pi^{\pm} J/\psi$ invariant mass distributions of the recent BESIII data on $e^+ e^- \to J/\psi \; \pi^+ \pi^-$ together with the $e^+ e^- \to J/\psi \; K^+K^-$ cross sections at $e^+e^-$ center-of-mass energies $q=4.23$ GeV and $q=4.26$ GeV. The rescattering effects between pions in the S and D-waves are taken into account through the Muskhelishvili-Omn\`es formalism. Since the physical region of the $\pi\pi$ invariant mass extends above 1 GeV, the important $K\bar{K}$ intermediate state in the S-wave is implemented through coupled-channel unitarity. For the left-hand cuts, we account for the well established charged exotic state $Z_c(3900)$ in $t$- and $u$-channels, while the other contributions are absorbed in the subtraction constants. For the $e^+ e^- \to J/\psi\, K \bar{K}$ we provide the prediction of the two-kaon invariant mass distribution. The constructed amplitudes serve as an essential framework to interpret the present and forthcoming measurements by the BESIII and Belle II Collaborations.

We present the SCUBA-2 850 ${\mu}m$ component of JINGLE, the new JCMT large survey for dust and gas in nearby galaxies, which with 193 galaxies is the largest targeted survey of nearby galaxies at 850 ${\mu}m$. We provide details of our SCUBA-2 data reduction pipeline, optimised for slightly extended sources, and including a calibration model adjusted to match conventions used in other far-infrared data. We measure total integrated fluxes for the entire JINGLE sample in 10 infrared/submillimetre bands, including all WISE, Herschel-PACS, Herschel-SPIRE and SCUBA-2 850 ${\mu}m$ maps, statistically accounting for the contamination by CO(J=3-2) in the 850 ${\mu}m$ band. Of our initial sample of 193 galaxies, 191 are detected at 250 ${\mu}m$ with a $\geq$ 5${\sigma}$ significance. In the SCUBA-2 850 ${\mu}m$ band we detect 126 galaxies with $\geq$ 3${\sigma}$ significance. The distribution of the JINGLE galaxies in far-infrared/sub-millimetre colour-colour plots reveals that the sample is not well fit by single modified-blackbody models that assume a single dust-emissivity index $(\beta)$. Instead, our new 850 ${\mu}m$ data suggest either that a large fraction of our objects require $\beta < 1.5$, or that a model allowing for an excess of sub-mm emission (e.g., a broken dust emissivity law, or a very cold dust component 10 K) is required. We provide relations to convert far-infrared colours to dust temperature and $\beta$ for JINGLE-like galaxies. For JINGLE the FIR colours correlate more strongly with star-formation rate surface-density rather than the stellar surface-density, suggesting heating of dust is greater due to younger rather than older stellar-populations, consistent with the low proportion of early-type galaxies in the sample., Comment: Accepted by MNRAS; data available at http://www.star.ucl.ac.uk/JINGLE/

In this work, we use the dispersion theory to provide a physical description of recent BESIII data on the reaction $ e^+ e^- \to \psi (2S) \, \pi^+ \, \pi^-$. Taking into account explicitly the effects of charged exotic intermediate states in the $t$- and $u$-channels as well as the two-pion final state interaction, we describe the invariant mass distribution for four different $e^+ e^-$ center-of-mass energies. The effects of the $\pi\pi$ rescattering are accounted for within a model-independent single channel approach which is found to explain the $\pi \pi$-invariant mass distributions at all $e^+ e^-$ center-of-mass energies. For $q= 4.226$ GeV and $q= 4.258$ GeV the already established charged exotic state $Z_c(3900)$ is considered as the intermediate state, whereas for $q= 4.358$ GeV the rescattering of pions dominates the fits. For the highest energy, $q= 4.416$ GeV, a heavier charged exotic state with mass $m_{Z_c} = 4.016(4)$ GeV and width $\Gamma_{Z_c} = 52(10)$ MeV is essential to describe the experimental data. Although the mass of this state is consistent with the established $Z_c(4020)$, its width is significantly larger.

Energetic feedback by Active Galactic Nuclei (AGNs) plays an important evolutionary role in the regulation of star formation (SF) on galactic scales. However, the effects of this feedback as a function of redshift and galaxy properties such as mass, environment and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high sensitivity (up to ten times higher than the Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred km) of the proposed next generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGNs and their role in galaxy evolution. Here, we provide an overview of the science related to AGN feedback that will be possible in the ngVLA era and present new continuum ngVLA imaging simulations of resolved radio jets spanning a wide range of intrinsic extents. We also consider key computational challenges and discuss exciting opportunities for multi-wavelength synergy with other next-generation instruments, such as the Square Kilometer Array and the James Webb Space Telescope. The unique combination of high-resolution, large collecting area, and wide frequency range will enable significant advancements in our understanding of the effects of jet-driven feedback on sub-galactic scales, particularly for sources with extents of a few pc to a few kpc such as young and/or lower-power radio AGNs, AGNs hosted by low-mass galaxies, radio jets that are interacting strongly with the interstellar medium of the host galaxy, and AGNs at high redshift., Comment: 26 pages, 9 figures, accepted for publication in ApJ

Using infrared data from the Herschel Space Observatory and Karl G. Jansky Very Large Array (VLA) 3 GHz observations in the COSMOS field, we investigate the redshift evolution of the infrared-radio correlation (IRRC) for star-forming galaxies (SFGs) we classify as either spheroid- or disc-dominated based on their morphology. The sample predominantly consists of disc galaxies with stellar mass ${\gtrsim}10^{10}\,M_{\odot}$, and residing on the star-forming main sequence (MS). After the removal of AGN using standard approaches, we observe a significant difference between the redshift-evolution of the median IR/radio ratio $\overline{q}_{\mathrm{TIR}}$ of (i) a sample of ellipticals, plus discs with a substantial bulge component (`spheroid-dominated' SFGs) and, (ii) virtually pure discs and irregular systems (`disc-dominated' SFGs). The spheroid-dominated population follows a declining $\overline{q}_{\mathrm{TIR}}$ vs. $z$ trend similar to that measured in recent evolutionary studies of the IRRC. However, for disc-dominated galaxies, where radio and IR emission should be linked to star formation in the most straightforward way, we measure very little change in $\overline{q}_{\mathrm{TIR}}$. This suggests that low-redshift calibrations of radio emission as an SFR-tracer may remain valid out to at least $z\,{\simeq}\,1\,{-}\,1.5$ for pure star-forming systems. We find that the different redshift-evolution of $q_{\rm TIR}$ for the spheroid- and disc-dominated sample is mainly due to an increasing radio excess for spheroid-dominated galaxies at $z\,{\gtrsim}\,$0.8, hinting at some residual AGN activity in these systems. This finding demonstrates that in the absence of AGN the IRRC is independent of redshift, and that radio observations can therefore be used to estimate SFRs at all redshifts for genuinely star-forming galaxies., Comment: Resubmitted to MNRAS after addressing reviewer feedback

HE0450-2958, an interacting quasar-starburst galaxy pair at $z$ = 0.285, is one of the best known examples of strong star formation activity in the presence of a quasar-driven jet. We present new multi-band JVLA-imaging covering 1 to 6 GHz and reaching an angular resolution of up to $0{}_{{}^.}^{"}6$ (a 6-fold improvement over existing radio data). We confirm the previous detection of a spatially extended radio component around the quasar indicating that there is on-going star formation activity in the quasar host galaxy. For the first time, we directly detect a jet-like bipolar outflow from the quasar aligned with its companion star-forming galaxy (SFG) and several blobs of ionized gas in its vicinity identified in previous studies. Within the companion SFG we find evidence for a flattening of the synchrotron spectral index towards the point of intersection with the jet axis, further suggesting that the outflow may actually be impacting its interstellar medium (ISM). We discuss two possible mechanisms that could have triggered the starburst in the companion SFG: a wet-dry merger with the quasar and jet-induced star formation. While triggering through interaction-driven gas dynamics cannot be excluded with current data, our new observations make HE0450-2958 a strong candidate for jet-induced star formation, and one of the rare links between local systems (like Minkowski's Object or Centaurus A) and the high-z regime where radio-optical alignments suggest that this phenomenon could be more common., Comment: 11 pages including 5 figures, published in MNRAS

Newly discovered Bi-O-S compounds remain an enigma in attempts to understand their electronic properties. A recent study of Bi$_{4}$O$_{4}$S$_{3}$ has shown it to be a mixture of two phases, Bi$_{2}$OS$_{2}$ and Bi$_{3}$O$_{2}$S$_{3}$, the latter being superconducting [W. A. Phelan et al., J. Am. Chem. Soc. 135, 5372 (2013)]. Using density functional theory, we explore the electronic structure of both the phases and the effect of the introduction of stacking faults. Our results demonstrate that the S$_{2}$ layers dope the bismuth-sulphur bands. The bands at the Fermi level are of clear two-dimensional character. One band manifold is confined to the two adjacent, square-lattice bismuth-sulphur planes, a second manifold is confined to the square lattice of sulphur dimers. We show that the introduction of defects in the stacking does not influence the electronic structure. Finally, we also show that spin-orbit coupling does not have any significant effect on the states close to the Fermi level at the energy scale considered.