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1. Resolved low- J 12CO excitation at 190 parsec resolution across NGC 2903 and NGC 3627

   https://doi.org/10.1093/mnras/stad3091  

   den Brok, J. S.; Leroy, A. K.; Usero, A.; Schinnerer, E.; Rosolowsky, E.; Koch, E. W.; Querejeta, M.; Liu, D.; Bigiel, F.; Barnes, A. T.; et al (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The low-J rotational transitions of 12CO are commonly used to trace the distribution of molecular gas in galaxies. Their ratios are sensitive to excitation and physical conditions in the molecular gas. Spatially resolved studies of CO ratios are still sparse and affected by flux calibration uncertainties, especially since most do not have high angular resolution or do not have short-spacing information and hence miss any diffuse emission. We compare the low-J CO ratios across the disc of two massive, star-forming spiral galaxies NGC 2903 and NGC 3627 to investigate whether and how local environments drive excitation variations at GMC scales. We use Atacama Large Millimeter Array (ALMA) observations of the three lowest-J CO transitions at a common angular resolution of 4 arcsec (190 pc). We measure median line ratios of $$R_{21}=0.67^{+0.13}_{-0.11}$$, $$R_{32}=0.33^{+0.09}_{-0.08}$$, and $$R_{31}=0.24^{+0.10}_{-0.09}$$ across the full disc of NGC 3627. We see clear CO line ratio variation across the galaxy consistent with changes in temperature and density of the molecular gas. In particular, towards the centre, R21, R32, and R31 increase by 35  per cent, 50  per cent, and 66  per cent, respectively, compared to their average disc values. The overall line ratio trends suggest that CO(3–2) is more sensitive to changes in the excitation conditions than the two lower J transitions. Furthermore, we find a similar radial R32 trend in NGC 2903, albeit a larger disc-wide average of $$\langle R_{32}\rangle =0.47^{+0.14}_{-0.08}$$. We conclude that the CO low-J line ratios vary across environments in such a way that they can trace changes in the molecular gas conditions, with the main driver being changes in temperature. 

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2. Dynamical masses and mass-to-light ratios of resolved massive star clusters – I. NGC 419 and NGC 1846

   https://doi.org/10.1093/mnras/stz2502  

   Song, Ying-Yi; Mateo, Mario; Mackey, A. D.; Olszewski, Edward W.; Roederer, Ian U.; Walker, Matthew G.; Bailey, III, John I. (September 2019, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT As an introduction of a kinematic survey of Magellanic Cloud (MC) star clusters, we report on the dynamical masses and mass-to-light ratios (M/L) of NGC 419 (Small Magellanic Cloud) and NGC 1846 (Large Magellanic Cloud). We have obtained more than one hundred high-resolution stellar spectra in and around each cluster using the multi-object spectrograph M2FS on the Magellan/Clay Telescope. Line-of-sight velocities and positions of the stars observed in each cluster were used as input to an expectation-maximization algorithm used to estimate cluster membership probabilities, resulting in samples of 46 and 52 likely members (PM ≥ 50 per cent) in NGC 419 and NGC 1846, respectively. This process employed single-mass King models constrained by the structural parameters of the clusters and provided self-consistent dynamical mass estimates for both clusters. Our best-fitting results show that NGC 419 has a projected central velocity dispersion of $$2.44^{+0.37}_{-0.21}$$ km s−1, corresponding to a total mass of $$7.6^{+2.5}_{-1.3}\times 10^4\ {\rm M}_{\odot }$$ and V-band M/L ratio of $$0.22^{+0.08}_{-0.05}$$ in solar units. For NGC 1846, the corresponding results are $$2.04^{+0.28}_{-0.24}$$ km s−1, $$5.4^{+1.5}_{-1.4}\times 10^4\ {\rm M}_{\odot }$$, and $$0.32^{+0.11}_{-0.11}$$. The mean metallicities of NGC 419 and NGC 1846 are found to be $$\rm [Fe/H]=-0.84\pm 0.19$$ and −0.70 ± 0.08, respectively, based on the spectra of likely cluster members. We find marginal statistical evidence of rotation in both clusters, though in neither cluster does rotation alter our mass estimates significantly. We critically compare our findings with those of previous kinematic studies of these two clusters in order to evaluate the consistency of our observational results and analytic tools. 

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3. Detection of the Diffuse H i Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

   https://doi.org/10.3847/1538-4357/ab97b9  

   Das, Sanskriti; Sardone, Amy; Leroy, Adam K.; Mathur, Smita; Gallagher, Molly; Pingel, Nickolas M.; Pisano, D. J.; Heald, George (July 2020, The Astrophysical Journal)

   null (Ed.)
4. Properties of supernova remnants in SIGNALS galaxies – I. NGC 6822 and M33

   https://doi.org/10.1093/mnras/stae1641  

   Duarte Puertas, Salvador; Drissen, Laurent; Robert, Carmelle; Rousseau-Nepton, Laurie; Martin, René_Pierre; Amram, Philippe; Martin, Thomas (July 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present a spatially resolved study of the kinematical properties of known supernova remnants (SNRs) in the nearest galaxies of the SIGNALS survey, namely NGC 6822 (one object) and M33 (163 objects), based on data obtained with the SITELLE imaging Fourier transform spectrometer at the Canada–France–Hawaii Telescope. The purpose of this paper is to provide a better scheme of identification for extragalactic SNRs and, in particular, to distinguish between H ii regions and SNRs. For that we have used diagrams which involve both the [S ii]/H$$\alpha$$ ratio and the velocity dispersion ($$\sigma$$). We also introduce a new parameter, $$\xi = {[\rm S\, {\small II}] \over H\alpha } \times \sigma$$, which enhances still the contrast between SNRs and the rest of the ionized gas. More than 90 per cent of the SNRs in our entire sample show an integrated [S ii]/H$$\alpha$$ ratio larger than the canonical value (0.4). 86 per cent of the SNRs present in our field show a significant velocity dispersion. The spectral resolution of our observations allows us to observe the complex velocity structure of some SNRs. 

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5. A new class of dark matter-free dwarf galaxies?: I. Clues from FCC 224, NGC 1052-DF2, and NGC 1052-DF4

   https://doi.org/10.1051/0004-6361/202453522  

   Buzzo, Maria Luisa; Forbes, Duncan A; Romanowsky, Aaron J; Haacke, Lydia; Gannon, Jonah S; Tang, Yimeng; Hilker, Michael; Ferré-Mateu, Anna; Janssens, Steven R; Brodie, Jean P; et al (March 2025, Astronomy & Astrophysics)

   The discovery of quiescent, dark matter (DM)-deficient ultra-diffuse galaxies (UDGs) with overluminous globular clusters (GCs) has challenged galaxy formation models within the Lambda cold dark matter (ΛCDM) cosmological paradigm. Previously, such galaxies were only identified in the NGC 1052 group, raising the possibility that they are the result of unique, group-specific processes, and limiting their broader significance. The recent identification of FCC 224, a putative DM-deficient UDG on the outskirts of the Fornax Cluster, suggests that such galaxies are not confined to the NGC 1052 group but rather represent a broader phenomenon. We aim to investigate the DM content of FCC 224 and to explore its similarities to the DM-free dwarfs in the NGC 1052 group, DF2 and DF4, to determine whether or not it belongs to the same class of DM-deficient UDGs. We use high-resolution Keck Cosmic Web Imager (KCWI) spectroscopy to study the kinematics, stellar populations, and GC system of FCC 224, enabling direct comparisons with DF2 and DF4. We find that FCC 224 is also DM-deficient and exhibits a distinct set of traits shared with DF2 and DF4, including slow and prolate rotation, quiescence in low-density environments, coeval formation of stars and GCs, flat stellar population gradients, a top-heavy GC luminosity function, and monochromatic GCs. These shared characteristics signal the existence of a previously unrecognised class of DM-deficient dwarf galaxies. This diagnostic framework provides a means of identifying additional examples and raises new questions for galaxy formation models within ΛCDM cosmology. 

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