arXiv subjects

Mark A. Thompson

Publications and source records attributed to Mark A. Thompson.

17 recordsLinked to original sources

arXiv2026

SKAO-ALMA Synergies in Star Formation Science

We highlight the potential for synergies between the SKA telescopes and ALMA, which will begin to be significant already with SKA Early Science. Broadly within star formation science, we focus on 1) (simultaneous) time domain and variability studies (e.g., of (proto-)stars), which is systematically opening a new observing window that will enable us to better constrain the physics of extreme stellar flares and their interplay with mass accretion in young stars, 2) possibilities for complementary coverage of different transitions of molecules as tracers of the ISM (e.g., H2CO to trace density and temperature), and 3) radio recombination lines to trace ionised gas at different densities. Furthermore, we address synergies in terms of the spatial resolution of both observatories and new capabilities not only on the SKAO side but extending to the ALMA2030 wideband sensitivity upgrade.

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arXiv2026

SMGPS: A study of Galactic HII regions with extended morphology

We present a study of ionised hydrogen ($\textrm{H}\scriptstyle\mathrm{II}$) regions in the Galactic Plane using data from the SARAO MeerKAT Galactic Plane Survey (SMGPS). The SMPGS is a wide-field, wide-band 1.3 GHz radio continuum survey ($251^\circ \leq l \leq 358^\circ$ and $2^\circ \leq l \leq 61^\circ$ at $\quad |b| \leq 1^\circ.5$) that has enabled us to trace the diffuse emission enveloping recently formed massive stars. Our multifrequency synthesis images reveal faint and extended emission that was previously overlooked by $\textrm{H}\scriptstyle\mathrm{II}$ region surveys. We report the distances and Lyman-photon flux ($N_{\mathrm{Ly}}$) measurements for 1,327 Galactic $\textrm{H}\scriptstyle\mathrm{II}$ regions from which we characterise the spectral types for candidate ionising stars. The spectral types range from B2 to O4. The typical stellar spectral type responsible for ionisation is the B0, which constitutes about $\text{16%}$ of our catalogue, corresponding to a mean $\log(N_{\mathrm{Ly}}) = 47.5\ \mathrm{s}^{-1}$. Moreover, as a result of the lack of radio recombination line (RRL) velocity measurements for faint $\textrm{H}\scriptstyle\mathrm{II}$ regions, we identify the effective completeness limit at $\log(N_{\mathrm{Ly}}) \approx 47.6\ \mathrm{s}^{-1}$. The multiwavelength approach reveals that the physical radius at 1.3 GHz and in the mid-infrared are well correlated with a slope of $1.15 \pm 0.02$. We find clear power-law relations between $N_{\mathrm{Ly}}$ and physical radius, and an inverse correlation between electron density and radius ($n_{\rm e} \propto R^{-0.73}$). However, no significant correlation is observed between the $N_{\mathrm{Ly}}$ and Galactocentric distance, suggesting that the observed trends are governed primarily by local star-forming environments rather than large-scale Galactic gradients.

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arXiv2025

H II regions and supernova remnants associated with molecular clouds: A pilot study with the SARAO MeerKAT Galactic Plane Survey

Massive stars (mass beyond 8 solMass) release vast amounts of energy into the interstellar medium through their stellar winds, photoionising radiation and supernova explosions. These processes may compress nearby regions, triggering further star formation, but the significance of triggered star formation across the Galactic disc is not well understood. This pilot study combines 1.3 GHz continuum data from the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) with 13CO (2-1) data from the Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM) survey to identify and examine molecular clouds associated with H II regions and supernovae remnants (SNRs). We focus on their physical properties and massive star formation potential. We identify 268 molecular clouds from the SEDIGISM tile covering the Galactic plane region between 341 and 343 longitude deg and latitude deg equal to or less 0.5, of which 90 clouds (34 per cent) are associated with SMGPS extended sources. Compared to unassociated clouds, we find that associated clouds exhibit significantly higher mean mass (9600 solMass vs. 2500 solMass ) and average gas surface density (104 solMass / pc^2 vs. 67 solMass / pc^2 ), and slightly elevated but comparable virial parameters. We also find that the size-linewidth scaling relation is steeper for associated clouds compared to unassociated clouds. In addition, radio luminosity shows a positive correlation with total complex mass, and the ratio L_radio/L_complex increases with source size, consistent with an evolutionary sequence where expanding H II regions progressively disrupt their natal molecular environment. These findings suggest an enhanced dynamical activity for the associated clouds and support the hypothesis that feedback from massive stars influences molecular cloud properties and may trigger star formation.

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arXiv2025

The SARAO MeerKAT Galactic Plane Survey compact source catalogue

We present a catalogue of compact sources detected in the SARAO MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). We extract 510599 compact sources, with areas less than five 8" beams, from the survey maps covering the regions $252\deg< l < 358^\deg$ and $2\deg < l < 61\deg$ at $|b| \leq 1.5^\deg$, which have an angular resolution of 8" and a sensitivity of $\sim$ 10-30 $\mu$Jy beam$^{-1}$. In this paper, we describe the source identification and characterisation methods, present the quality assurance of the catalogue, explore the nature of the catalogue sources, and present initial science highlights. We limit our catalogue to sources with a signal-to-noise ratio $\geq 5$, as the catalogue is $\sim$90 per cent complete, and has a false positive rate of less than 1 per cent at this threshold. The bulk of the catalogue sources are previously unknown to the literature, with the majority of unknown sources at sub-mJy levels. Initial science highlights from the catalogue include the detection of 213 radio quiet WISE HII region candidates, previously undetected in radio continuum studies. We show images that compare the SMGPS compact sources to CORNISH ultracompact HII regions, thus highlighting the sensitivity and unprecedented uv-coverage of the SMGPS, and the potential synergy of the SMGPS with other surveys.

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arXiv2025

The stellar population in the SARAO MeerKAT Galactic Plane Survey

We report on optically selected stellar candidates of SARAO MeerKAT 1.3 GHz radio continuum survey sources of the Galactic plane. Stellar counterparts to radio sources are selected by cross-matching the MeerKAT source positions with \textit{Gaia} DR3, using two approaches. The first approach evaluated the probability of chance alignments between the radio survey and \textit{Gaia} sources and used AllWISE infrared colour-colour information to select potential stellar candidates. The second approach utilized a Monte Carlo method to evaluate the cross-matching reliability probability, based on populations of known radio-emitting stars. From the combined approaches, we found 629 potential stellar counterparts, of which 169 have existing SIMBAD classifications, making it the largest Galactic plane radio-optical crossmatch sample to date. A colour-magnitude analysis of the sample revealed a diverse population of stellar objects, ranging from massive OB stars, main-sequence stars, giants, young stellar objects, emission line stars, red dwarfs and white dwarfs. Some of the proposed optical counterparts include chromospherically/coronally active stars, for example RS CVn binaries, BY Dra systems, YSOs and flare stars, which typically exhibit radio emission. Based on Gaia's low-resolution spectroscopy, some of the stars show strong H$\alpha$ emission, indicating they are magnetically active, consistent with them being radio emitters. While MeerKAT's sensitivity and survey speed make it ideal for detecting faint radio sources, its angular resolution limits accurate counterpart identification for crowded fields such as the Galactic Plane. Higher frequency, and, thereby, better spatial resolution, radio observations plus circular polarization would be required to strengthen the associations.

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arXiv2025

Mining the time axis with TRON. II. MeerKAT detects a stellar radio flare from a distant RS CVn candidate

Medium-timescale (minutes to hours) radio transients are a relatively unexplored population. The wide field-of-view and high instantaneous sensitivity of instruments such as MeerKAT provides an opportunity to probe this class of sources, using image-plane detection techniques. The previous letter in this series describes our project and associated TRON pipeline designed to mine archival MeerKAT data for transient and variable sources. In this letter, we report on a new transient, a radio flare, associated with Gaia DR3 6865945581361480448, a G type star, whose parallax places it at a distance of 1334 pc. Its duration and high degree of circular polarization suggests electron cyclotron maser instability as the mechanism, consistent with an RS CVn variable.

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arXiv2024

The SARAO MeerKAT Galactic Plane Survey filamentary source catalogue

We present a catalogue of filamentary structures identified in the SARAO (South African Radio Astronomy Observatory) MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). We extract 933 filaments across the survey area, 803 of which (~86%) are associated with extended radio structures (e.g. supernova remnants and HII regions), whilst 130 (~14%) are largely isolated. We classify filaments as thermal or non-thermal via their associated mid-infrared emission and find 77/130 (~59%) of the isolated sources are likely to be non-thermal, and are therefore excellent candidates for the first isolated, non-thermal radio filaments observed outside of the Galactic Centre (GC). Comparing the morphological properties of these non-thermal candidates to the non-thermal filaments observed towards the GC we find the GC filaments are on the whole angularly narrower and shorter than those across the SMGPS, potentially an effect of distance. The SMGPS filaments have flux densities similar to those of the GC, however the distribution of the latter extends to higher flux densities. If the SMGPS filaments were closer than the GC population, it would imply a more energetic population of cosmic ray electrons in the GC. We find the filament position angles in the SMGPS are uniformly distributed, implying that the local magnetic field traced by the filaments does not follow the large-scale Galactic field. Finally, although we have clearly shown that filaments are not unique to the GC, the GC nevertheless has the highest density of filaments in the Milky Way.

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arXiv2024

PAMS: The Perseus Arm Molecular Survey -- I. Survey description and first results

The external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in $^{12}$CO, $^{13}$CO, and C$^{18}$O ($J$=3-2). With a survey area of $\sim$8 deg$^2$, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at $\ell \approx 110^{\circ}$ and $\ell \approx 135^{\circ}$. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of $T_\mathrm{mb} = 0.7$-1.0 K in 0.3 km s$^{-1}$ channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H$_2$ column density from Herschel, we calculate representative values for the CO-to-H$_2$ column-density $X$-factors, which are $X_{^{12}\mathrm{CO (3-2)}}=4.0\times10^{20}$ and $X_{^{13}\mathrm{CO (3-2)}}=4.0\times10^{21}$cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth and mass-radius relationships of $^{13}$CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the $X$-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.

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arXiv2024

Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Our Galaxy

As we learn more about the multi-scale interstellar medium (ISM) of our Galaxy, we develop a greater understanding for the complex relationships between the large-scale diffuse gas and dust in Giant Molecular Clouds (GMCs), how it moves, how it is affected by the nearby massive stars, and which portions of those GMCs eventually collapse into star forming regions. The complex interactions of those gas, dust and stellar populations form what has come to be known as the ecology of our Galaxy. Because we are deeply embedded in the plane of our Galaxy, it takes up a significant fraction of the sky, with complex dust lanes scattered throughout the optically recognisable bands of the Milky Way. These bands become bright at (sub-)millimetre wavelengths, where we can study dust thermal emission and the chemical and kinematic signatures of the gas. To properly study such large-scale environments, requires deep, large area surveys that are not possible with current facilities. Moreover, where stars form, so too do planetary systems, growing from the dust and gas in circumstellar discs, to planets and planetesimal belts. Understanding the evolution of these belts requires deep imaging capable of studying belts around young stellar objects to Kuiper belt analogues around the nearest stars. Here we present a plan for observing the Galactic Plane and circumstellar environments to quantify the physical structure, the magnetic fields, the dynamics, chemistry, star formation, and planetary system evolution of the galaxy in which we live with AtLAST; a concept for a new, 50m single-dish sub-mm telescope with a large field of view which is the only type of facility that will allow us to observe our Galaxy deeply and widely enough to make a leap forward in our understanding of our local ecology.

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arXiv2024

The dynamic centres of infrared-dark clouds and the formation of cores

High-mass stars have an enormous influence on the evolution of the interstellar medium in galaxies, so it is important that we understand how they form. We examine the central clumps within a sample of seven infrared-dark clouds (IRDCs) with a range of masses and morphologies. We use 1 pc-scale observations from NOEMA and the IRAM 30-m telescope to trace dense cores with 2.8 mm continuum, and gas kinematics in C$^{18}$O, HCO$^+$, HNC, and N$_2$H$^+$ ($J$=1$-$0). We supplement our continuum sample with six IRDCs observed at 2.9 mm with ALMA, and examine the relationships between core- and clump-scale properties. We have developed a fully-automated multiple-velocity component hyperfine line-fitting code called mwydyn which we employ to trace the dense gas kinematics in N$_2$H$^+$ (1$-$0), revealing highly complex and dynamic clump interiors. We find that parsec-scale clump mass is the most important factor driving the evolution; more massive clumps are able to concentrate more mass into their most massive cores - with a log-normally distributed efficiency of around 9% - in addition to containing the most dynamic gas. Distributions of linewidths within the most massive cores are similar to the ambient gas, suggesting that they are not dynamically decoupled, but are similarly chaotic. A number of studies have previously suggested that clumps are globally collapsing; in such a scenario, the observed kinematics of clump centres would be the direct result of gravity-driven mass inflows that become ever more complex as the clumps evolve, which in turn leads to the chaotic mass growth of their core populations.

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arXiv2022

Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2

In this study, 36 cores (30 starless and 6 protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in the $J = 1\rightarrow0$ transitions of HCO$^+$, H$^{13}$CO$^+$, N$_2$H$^+$, HNC, and HN$^{13}$C. The asymmetry parameter $δV$, which was the ratio of the difference between the HCO$^+$ and H$^{13}$CO$^+$ peak velocities to the H$^{13}$CO$^+$ line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blue-shifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO$^+$ and H$^{13}$CO$^+$ of them was up to 0.9 km s$^{-1}$, suggesting that some inward motions exceeded the speed of sound for the quiescent gas ($\sim10-17$ K). The mean of $δV$ of the five aforementioned starless cores was derived to be $-$0.5$\pm$0.3. One core, G211.16$-$19.33North3, observed using the ALMA ACA in DCO$^+$ $J = 3\rightarrow2$ exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO$^+$ $J = 3\rightarrow2$ line was larger ($\sim 0.5$ km s$^{-1}$) than that in HCO$^+$ $J = 1\rightarrow0$ ($\sim 0.2$ km s$^{-1}$), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).

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arXiv2021

Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey

We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules, N$_2$H$^+$, HC$_3$N, and CCS at 82$-$94 GHz using the Nobeyama 45-m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N$_2$H$^+$ and HC$_3$N line emissions are approximately similar to that of 850-$μ$m dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850-$μ$m dust continuum emission. Occasionally (12%), we observe the CCS emission which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect nonthermal velocity dispersion.

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arXiv2020

Molecular Cloud Cores with High Deuterium Fraction: Nobeyama Single-Pointing Survey

We present the results of a single-pointing survey of 207 dense cores embedded in Planck Galactic Cold Clumps distributed in five different environments ($λ$ Orionis, Orion A, B, Galactic plane, and high latitudes) to identify dense cores on the verge of star formation for the study of the initial conditions of star formation. We observed these cores in eight molecular lines at 76-94 GHz using the Nobeyama 45-m telescope. We find that early-type molecules (e.g., CCS) have low detection rates and that late-type molecules (e.g., N$_2$H$^+$, c-C$_3$H$_2$) and deuterated molecules (e.g., N$_2$D$^+$, DNC) have high detection rates, suggesting that most of the cores are chemically evolved. The deuterium fraction (D/H) is found to decrease with increasing distance, indicating that it suffers from differential beam dilution between the D/H pair of lines for distant cores ($>$1 kpc). For $λ$ Orionis, Orion A, and B located at similar distances, D/H is not significantly different, suggesting that there is no systematic difference in the observed chemical properties among these three regions. We identify at least eight high D/H cores in the Orion region and two at high latitudes, which are most likely to be close to the onset of star formation. There is no clear evidence of the evolutionary change in turbulence during the starless phase, suggesting that the dissipation of turbulence is not a major mechanism for the beginning of star formation as judged from observations with a beam size of 0.04 pc.

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arXiv2020

ALMA ACA and Nobeyama observations of two Orion cores in deuterated molecular lines

We mapped two molecular cloud cores in the Orion A cloud with the ALMA ACA 7-m Array and with the Nobeyama 45-m radio telescope. These cores have bright N$_2$D$^+$ emission in single-pointing observations with the Nobeyama 45-m radio telescope, have relatively high deuterium fraction, and are thought to be close to the onset of star formation. One is a star-forming core, and the other is starless. These cores are located along filaments observed in N$_2$H$^+$, and show narrow linewidths of 0.41 km s$^{-1}$ and 0.45 km s$^{-1}$ in N$_2$D$^+$, respectively, with the Nobeyama 45-m telescope. Both cores were detected with the ALMA ACA 7m Array in the continuum and molecular lines at Band 6. The starless core G211 shows clumpy structure with several sub-cores, which in turn show chemical differences. Also, the sub-cores in G211 have internal motions that are almost purely thermal. The starless sub-core G211D, in particular, shows a hint of the inverse P Cygni profile, suggesting infall motion. The star-forming core G210 shows an interesting spatial feature of two N$_2$D$^+$ peaks of similar intensity and radial velocity located symmetrically with respect to the single dust continuum peak. One interpretation is that the two N$_2$D$^+$ peaks represent an edge-on pseudo-disk. The CO outflow lobes, however, are not directed perpendicular to the line connecting both N$_2$D$^+$ peaks.

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arXiv2019

Probing the initial conditions of high-mass star formation. III. Fragmentation and triggered star formation

Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby HII regions. We present a high angular resolution study of a sample of 8 massive proto-cluster clumps. Combining infrared data, we use few-arcsecond resolution radio- and millimeter interferometric data to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring HII regions. Taking advantage of that, we test triggered star formation using a novel method where we study the alignment of the centres of mass traced by dust emission at multiple scales. The eight massive clumps have masses ranging from 228 to 2279 $M_\odot$. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of $R_{\rm eff}$ $\sim$ 0.02 pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8 $M_\odot$ at small scale of $R_{\rm eff}$ $\sim$ 0.02 pc. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale ($\sim$ 1 pc). We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.

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arXiv2014

VISTA Variables in the Vía Láctea (VVV): Halfway Status and Results

The VISTA Variables in the Vía Láctea (VVV) survey is one of six public ESO surveys, and is now in its 4th year of observing. Although far from being complete, the VVV survey has already delivered many results, some directly connected to the intended science goals (detection of variables stars, microlensing events, new star clusters), others concerning more exotic objects, e.g. novae. Now, at the end of the fourth observing period, and comprising roughly 50% of the proposed observations, the actual status of the survey, as well some of the results based on the VVV data, are presented.

astro-ph.IM↗

arXiv2003

Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.

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