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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:

Understanding the demographics of intermediate-mass black holes (IMBHs, MBH ≈ 102–105 M⊙) in low-mass galaxies is key to constraining black hole seed formation models, but detecting them is challenging due to their small gravitational sphere of influence (SOI). The upcoming Extremely Large Telescope (ELT) High Angular Resolution Monolithic Optical and Near-infrared Integral Field Spectrograph (HARMONI) instrument, with its high angular resolution, offers a promising solution. We present simulations assessing HARMONI’s ability to measure IMBH masses in nuclear star clusters (NSCs) of nearby dwarf galaxies. We selected a sample of 44 candidates within 10 Mpc. For two representative targets, NGC 300 and NGC 3115 dw01, we generated mock HARMONI integral-field data cubes using realistic inputs derived from Hubble Space Telescope imaging, stellar population models, and Jeans anisotropic models (JAM), assuming IMBH masses up to 1% of the NSC mass. We simulated observations across six near-infrared gratings at 10 mas resolution. Analyzing the mock data with standard kinematic extraction and JAM models in a Bayesian framework, we demonstrate that HARMONI can resolve the IMBH SOI and accurately recover masses down to ≈0.5% of the NSC mass within feasible exposure times. These results highlight HARMONI’s potential to revolutionize IMBH studies.

Abstract:

Dust is a fundamental component of the interstellar medium within galaxies, as dust grains are highly efficient absorbers of ultraviolet (UV) and optical photons. Accurately quantifying this obscuration is crucial for interpreting galaxy spectral energy distributions (SEDs). The extinction curves in the Milky Way (MW) and Large Magellanic Cloud exhibit a strong feature known as the 2175 Ã… UV bump, most often attributed to small carbonaceous dust grains. This feature was recently detected in faint galaxies out to , suggesting rapid formation channels. Here, we report the detection of a strong UV bump in a luminous Lyman-break galaxy at , GNWY-7379420231, through observations taken as part of the NIRSpec Wide GTO survey. We fit a dust attenuation curve that is consistent with the MW extinction curve within , in a galaxy just Myr after the big bang. From the integrated spectrum, we infer a young mass-weighted age ( Myr) for this galaxy, however spatially resolved SED fitting unveils the presence of an older stellar population ( Myr). Furthermore, morphological analysis provides evidence for a potential merger. The underlying older stellar population suggests the merging system could be pre-enriched, with the dust illuminated by a merger-induced starburst. Moreover, turbulence driven by stellar feedback in this bursty region may be driving polycyclic aromatic hydrocarbon formation through top-down shattering. The presence of a UV bump in GNWY-7379420231 solidifies growing evidence for the rapid evolution of dust properties within the first billion years of cosmic time.

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.