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Aims. In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9+3.1. Methods. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9+3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant. Results. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9+3.1 is estimated to be 0.42±0.03 and the integrated flux density at 1 GHz to be around 2.7 Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shelllike X-ray morphology of G5.9+3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density N H ∼ 0.80 × 10 22 cm −2 and fitted temperatures spanning the range kT ∼ 0.14 − 0.23 keV for all of the regions. The derived electron number densities n e for the whole SNR and the rims are also roughly comparable (ranging from ∼ 0.20 f −1/2 cm −3 to ∼ 0.40 f −1/2 cm −3 , where f is the volume filling factor). We also estimate the swept-up mass of the X-ray emitting plasma associated with G5.9+3.1 to be ∼ 46 f −1/2 M ⊙ .

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Galaxy populations show bimodality in a variety of properties: stellar mass, colour, specific star-formation rate, size, and Sérsic index. These parameters are our feature space. We use an existing sample of 7556 galaxies from the Galaxy and Mass Assembly (GAMA) survey, represented using five features and the K-means clustering technique, showed that the bimodalities are the manifestation of a more complex population structure, represented by between 2 and 6 clusters. Here we use Self Organizing Maps (SOM), an unsupervised learning technique which can be used to visualize similarity in a higher dimensional space using a 2D representation, to map these five-dimensional clusters in the feature space on to two-dimensional projections. To further analyse these clusters, using the SOM information, we agree with previous results that the sub-populations found in the feature space can be reasonably mapped on to three or five clusters. We explore where the ‘green valley’ galaxies are mapped on to the SOM, indicating multiple interstitial populations within the green valley population. Finally, we use the projection of the SOM to verify whether morphological information provided by GalaxyZoo users, for example, if features are visible, can be mapped on to the SOM-generated map. Voting on whether galaxies are smooth, likely ellipticals, or ‘featured’ can reasonably be separated but smaller morphological features (bar, spiral arms) can not. SOMs promise to be a useful tool to map and identify instructive sub-populations in multidimensional galaxy survey feature space, provided they are large enough.

Understanding the effect spiral structure has on star formation properties of galaxies is important to complete our picture of spiral structure evolution. Previous studies have investigated connections between spiral arm properties and star formation, but the effect that the number of spiral arms has on this process is unclear. Here, we use the Galaxy And Mass Assembly (GAMA) survey paired with the citizen science visual classifications from the Galaxy Zoo project to explore galaxies’ spiral arm number and how it connects to the star formation process. We use the votes from the GAMA-Kilo Degree Survey Galaxy Zoo classification to investigate the link between spiral arm number and stellar mass, star formation rate, and specific star formation rate (sSFR). We find that galaxies with fewer spiral arms have lower stellar masses and higher sSFRs, while those with more spiral arms tend towards higher stellar masses and lower sSFRs, and conclude that galaxies are less efficient at forming stars if they have more spiral arms. We note how previous studies’ findings may indicate a cause for this connection in spiral arm strength or opacity.

We present an analysis of spatially resolved gas-phase metallicity relations in five dwarf galaxies ($\rm M_{halo} \approx 10^{11}\, {\rm M}_\odot$, $\rm M_\star \approx 10^{8.8}-10^{9.6}\, {\rm M}_\odot$) from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, which include an explicit model for sub-grid turbulent mixing of metals in gas, near z ≈ 0, over a period of 1.4 Gyr, and compare our findings with observations. While these dwarf galaxies represent a diverse sample, we find that all simulated galaxies match the observed mass-metallicity (MZR) and mass-metallicity gradient (MZGR) relations. We note that in all five galaxies, the metallicities are effectively identical between phases of the interstellar medium (ISM), with 95${{\ \rm per\ cent}}$ of the gas being within ±0.1 dex between the cold and dense gas (T < 500 K and nH > 1 cm−3), ionized gas (near the HαT ≈ 104 K ridge-line), and nebular regions (ionized gas where the 10 Myr-averaged star formation rate is non-zero). We find that most of the scatter in relative metallicity between cold dense gas and ionized gas/nebular regions can be attributed to either local starburst events or metal-poor inflows. We also note the presence of a major merger in one of our galaxies, m11e, with a substantial impact on the metallicity distribution in the spatially resolved map, showing two strong metallicity peaks and triggering a starburst in the main galaxy.

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Galaxies fall broadly into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ‘green valley’. Some of these galaxies are suspected to be in the process of ceasing their star formation through a gradual exhaustion of gas supply, or already dead and experiencing a rejuvenation of star formation through fuel injection. We use the Galaxy And Mass Assembly (GAMA) database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley with those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found that disc features such as rings and lenses are more prominently represented in the green-valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new Kilo-Degree Survey (KiDS) images. Our aim is to compare the results from expert classification qualitatively with those of citizen science. We observe that ring structures are indeed found more commonly in green-valley galaxies compared with their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting the characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral-arm structure.