91̽»¨

Abstract:

The Sculptor galaxy, NGC 253, is the southern massive star-forming disk galaxy that is closest to the Milky Way. We present a new 103-pointing MUSE mosaic of this galaxy that covers most of its star-forming disk up to 0.75 × R 25 . With an area of ∼20 × 5 arcmin 2 (∼20 × 5 kpc 2 , projected) and a physical resolution of ∼15 pc, this mosaic constitutes one of the largest integral field spectroscopy surveys with the highest physical resolution of any star-forming galaxy to date. We exploited the mosaic to identify a sample of ∼500 planetary nebulae (the sample is ∼20 times larger than in previous studies) to build the planetary nebula luminosity function (PNLF) and obtain a new estimate of the distance to NGC 253. The value we obtained is 17% higher than the estimates returned by other reliable measurements, which were mainly obtained via the top of the red giant branch method. The PNLF also varies between the centre ( r < 4 kpc) and the disk of the galaxy. The distance derived from the PNLF of the outer disk is comparable to that of the full sample, while the PNLF of the centre returns a distance that is larger by ∼0.9 Mpc. Our analysis suggests that extinction related to the dust-rich interstellar medium and edge-on view of the galaxy (the average E ( B − V ) across the disk is ∼0.35 mag) plays a major role in explaining both the larger distance recovered from the full PNLF and the difference between the PNLFs in the centre and the disk.

Abstract:

Recent JWST mid-infrared (mid-IR) images, tracing polycyclic aromatic hydrocarbons (PAHs) and dust continuum emission, provide detailed views of the interstellar medium (ISM) in nearby galaxies. Leveraging PHANGS-JWST Cycle 1 and PHANGS-MUSE data, we measure the PAH and dust continuum emission lifetimes of gas clouds across 17 nearby star-forming galaxies by analyzing the relative spatial distributions of mid-IR (7.7–11.3 μm) and Hα emission at various scales. We find that the mid-IR emitting timescale of gas clouds in galactic disks (excluding centers) ranges from 10–30 Myr. After star formation is detected in Hα, mid-IR emission persists for 3–7 Myr during the stellar feedback phase, covering 70%–80% of the Hα emission. This significant overlap is due to intense radiation from star-forming regions, illuminating the surrounding PAHs and dust grains. In most galaxies, the mid-IR time-scale closely matches the molecular cloud lifetime measured with CO. Although mid-IR emission is complex, as influenced by ISM distribution, radiation, and abundances of dust and PAHs, the similarity between the two timescales suggests that once gas clouds form with compact mid-IR emission, they quickly provide sufficient shielding for stable CO formation. This is likely due to our focus on molecular gas-rich regions of galaxies with near-solar metallicity. Finally, we find that the mid-IR emitting timescale is longer in galaxies with well-defined H ii regions and less structured backgrounds, allowing photons to more efficiently heat the ambient ISM surrounding the H ii regions, rather than contributing to diffuse emission. This suggests that the shape of the ISM also influences mid-IR emission.

Abstract:

We present high-resolution ( or pc) Atacama Large Millimeter/sub-millimeter Array CO(J = 2–1) observations of the spiral galaxy NGC 5064. Our study identifies 478 molecular clouds, of which 387 are resolved both spatially and spectrally. These clouds exhibit similarities to those of the Milky Way in terms of their sizes, molecular gas masses, velocity dispersions, velocity gradients, and Larson relations. However, the NGC 5064 clouds stand out with slightly higher gas mass surface densities, lower virial parameters ( assuming a standard conversion factor cm (K km s; for a lower conversion factor of cm (K km s), and an unusually high fraction of retrograde rotation (). Retrograde clouds are 18 per cent larger, 58 per cent more massive, 15 per cent more turbulent and have 17 per cent larger gas mass surface densities than prograde clouds. The velocity gradients in the clouds seem to arise from turbulence rather than cloud’s intrinsic rotation or large-scale galaxy rotation. Cloud–cloud collisions provide the most plausible explanation for the elevated retrograde fraction, though further investigation is needed to confirm this scenario. Projection effects due to the galaxy’s high inclination () may further enhance the apparent retrograde fraction. Confirmation using less inclined systems is essential to determine whether the observed dominance of retrograde rotation reflects a genuine physical phenomenon or is significantly shaped by projection effects.

Abstract:

CO(1–0) and CO(2–1) are commonly used as bulk molecular gas tracers. The CO line ratios (especially CO(2–1)/CO(1–0)–R21) vary within and among galaxies, yet previous studies on R21 and alike often rely on measurements constructed by combining data from facilities with substantial relative calibration uncertainties that have the same order as physical line ratio variations. Hence, robustly determining systematic R21 variations is challenging. Here, we compare CO(1–0) and CO(2–1) mapping data from ALMA for 14 nearby galaxies, at a common physical resolution of 1.7 kpc. Our data set includes new ALMA (7 m+TP) CO(1–0) maps of 12 galaxies. We investigate R21 variation to understand its dependence on global galaxy properties, kiloparsec-scale environmental factors, and its correlation with star formation rate (SFR) surface density and metallicity. We find that the galaxy-to-galaxy scatter is 0.05 dex. This is lower than previous studies, which reported over 0.1 dex variation, likely reflecting significant flux calibration uncertainties in single-dish surveys. Within individual galaxies, R21 has a typical mean value of ∼0.64 and 0.1 dex variation, with an increase to ∼0.75 toward galactic centers. We find strong correlations between R21 and various galactic parameters, particularly SFR surface density, which shows a power-law slope of 0.10–0.11 depending on the adopted binning/fitting methods. Our findings suggest that, for studies covering main-sequence galaxy samples, assuming a fixed R21 = 0.64 does not significantly bias kiloparsec-scale molecular gas mass estimates from CO(2–1). Instead, systematic uncertainties from flux calibration and the CO-to-H2 conversion factor account for more systematic scatter of CO-derived molecular gas properties.

Abstract:

We present the Local Group L-Band Survey, a Karl G. Jansky Very Large Array (VLA) survey producing the highest-quality 21 cm and 1–2 GHz radio continuum images to date, for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA’s spectral multiplexing power, we simultaneously survey the 21 cm line at high 0.4 km s−1 velocity resolution, the 1–2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC 6822, IC 10, IC 1613, and the Wolf–Lundmark–Melotte Galaxy, we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of <5″ (10–20 pc) for the 21 cm line with <1020 cm−2 column density sensitivity, and even sharper views (<2″; 5–10 pc) of the continuum. Targeting these nearby galaxies (D ≲ 1 Mpc) reveals a sharp, resolved view of the atomic gas, including 21 cm absorption, and continuum emission from supernova remnants and H ii regions. These data sets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21 cm H i data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest-physical-resolution 21 cm observations of any external galaxies beyond the LMC and SMC.