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Molecular gas scaling relations for local star-forming galaxies in the low-M<SUB>*</SUB> regimeWe derived molecular gas fractions (f<SUB>mol</SUB> = M<SUB>mol</SUB>/M<SUB>*</SUB>) and depletion times (τ<SUB>mol</SUB> = M<SUB>mol</SUB>/SFR) for 353 galaxies representative of the local star-forming population with 10<SUP>8.5</SUP> M<SUB>⊙</SUB> < M<SUB>*</SUB> < 10<SUP>10.5</SUP> M<SUB>⊙</SUB> drawn from the ALLSMOG and xCOLDGASS surveys of CO(2−1) and CO(1−0) line emission. By adding constraints from low-mass galaxies and upper limits for CO non-detections, we find the median molecular gas fraction of the local star-forming population to be constant at log f<SUB>mol</SUB> = −0.99<SUB>−0.19</SUB><SUP>+0.22</SUP>, challenging previous reports of increased molecular gas fractions in low-mass galaxies. Above M<SUB>*</SUB> ∼ 10<SUP>10.5</SUP> M<SUB>⊙</SUB>, we find the f<SUB>mol</SUB> versus M<SUB>*</SUB> relation to be sensitive to the selection criteria for star-forming galaxies. We tested the robustness of our results against different prescriptions for the CO-to-H<SUB>2</SUB> conversion factor and different selection criteria for star-forming galaxies. The depletion timescale τ<SUB>mol</SUB> weakly depends on M<SUB>*</SUB>, following a power law with a best-fit slope of 0.16 ± 0.03. This suggests that small variations in specific star formation rate (sSFR = SFR/M<SUB>*</SUB>) across the local main sequence of star-forming galaxies with M<SUB>*</SUB> < 10<SUP>10.5</SUP> M<SUB>⊙</SUB> are mainly driven by differences in the efficiency of converting the available molecular gas into stars. We tested these results against a possible dependence of f<SUB>mol</SUB> and τ<SUB>mol</SUB> on the surrounding (group) environment of the targets by splitting them into centrals, satellites, and isolated galaxies, and find no significant variation between these populations. We conclude that the group environment is unlikely to have a large systematic effect on the molecular gas content of star-forming galaxies in the local Universe.
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Decomposing the AIA 304 Å Channel into Its Cool and Hot ComponentsThe AIA 304 Å channel on board the Solar Dynamics Observatory (SDO) offers a unique view of ≈10<SUP>5</SUP> K plasma emitting in the He II 304 Å line. However, when observing off-limb, the emission of the (small) cool structures in the solar atmosphere (such as spicules, coronal rain and prominence material) can be of the same order as the surrounding hot coronal emission from other spectral lines included in the 304 Å passband, particularly over active regions. In this paper, we investigate three methods based on temperature and morphology that are able to distinguish the cool and hot emission within the 304 Å passband. The methods are based on the Differential Emission Measure (DEM), a linear decomposition of the AIA response functions (RFit) and the Blind Source Separation (BSS) technique. All three methods are found to produce satisfactory results in both quiescent and flaring conditions, largely removing the diffuse corona and leading to images with cool material off-limb in sharp contrast with the background. We compare our results with co-aligned data from the Interface Region Imaging Spectrograph (IRIS) in the SJI 1400 Å and 2796 Å channels, and find the RFit method to best match the quantity and evolution of the cool material detected with IRIS. Some differences can appear due to plasma emitting in the logT =5.1 -5.5 temperature range, particularly during the catastrophic cooling stage prior to rain appearance during flares. These methods are, in principle, applicable to any passband from any instrument suffering from similar cool and hot emission ambiguity, as long as there is good coverage of the high-temperature range.
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Feasibility of meteor surveying from a Venus orbiterMeteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5× to 2.5× higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun.
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Feasibility of meteor surveying from a Venus orbiterMeteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5× to 2.5× higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun.
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A study of Galactic Plane Planck Galactic cold clumps observed by SCOPE and the JCMT Plane SurveyWe have investigated the physical properties of Planck Galactic Cold Clumps (PGCCs) located in the Galactic Plane, using the JCMT Plane Survey (JPS) and the SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. By utilizing a suite of molecular-line surveys, velocities, and distances were assigned to the compact sources within the PGCCs, placing them in a Galactic context. The properties of these compact sources show no large-scale variations with Galactic environment. Investigating the star-forming content of the sample, we find that the luminosity-to-mass ratio (L/M) is an order of magnitude lower than in other Galactic studies, indicating that these objects are hosting lower levels of star formation. Finally, by comparing ATLASGAL sources that are associated or are not associated with PGCCs, we find that those associated with PGCCs are typically colder, denser, and have a lower L/M ratio, hinting that PGCCs are a distinct population of Galactic Plane sources.
