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Abstract The Central Molecular Zone (CMZ) of the Milky Way is fed by gas inflows from the Galactic disk along almost radial trajectories aligned with the major axis of the Galactic bar. However, despite being fundamental to all processes in the nucleus of the Galaxy, these inflows have been studied significantly less than the CMZ itself. We present observations of various molecular lines between 215 and 230 GHz for 20 clouds with ∣ℓ∣ < 10°, which are candidates for clouds in the Galactic bar due to their warm temperatures and broad lines relative to typical Galactic disk clouds, using the Atacama Large Millimeter/submillimeter Array Atacama Compact Array. We measure gas temperatures, shocks, star formation rates, turbulent Mach numbers, and masses for these clouds. Although some clouds may be in the Galactic disk despite their atypical properties, nine clouds are likely associated with regions in the Galactic bar, and in these clouds, turbulent pressure is suppressing star formation. In clouds with no detected star formation, turbulence is the dominant heating mechanism, whereas photoelectric processes heat the star-forming clouds. We find that the ammonia (NH₃) and formaldehyde (H₂CO) temperatures probe different gas components, and in general, each transition appears to trace different molecular gas phases within the clouds. We also measure the CO-to-H₂X-factor in the bar to be an order of magnitude lower than the typical Galactic value. These observations provide evidence that molecular clouds achieve CMZ-like properties before reaching the CMZ. 

ABSTRACT In this paper, we study the filamentary substructure of 3.3 $$\mu$$m polycyclic aromatic hydrocarbon (PAH) emission from JWST/NIRCam observations in the base of the M 82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $$\sim$$50 pc. Several of those plumes extend to the edge of the field-of-view, and thus are at least 200–300 pc in length. In this region of the outflow, the vast majority ($$\sim$$70 per cent) of PAH emission is associated with the plumes. We show that those structures contain smaller scale ‘clouds’ with widths that are $$\sim$$5–15 pc, and they are morphologically similar to the results of ‘cloud-crushing’ simulations. We estimate the cloud-crushing time-scales of $$\sim$$0.5–3 Myr, depending on assumptions. We show this time-scale is consistent with a picture in which these observed PAH clouds survived break-out from the disc rather than being destroyed by the hot wind. The PAH emission in both the mid-plane and the outflow is shown to tightly correlate with that of Pa $$\alpha$$ emission (from Hubble Space Telescope data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa $$\alpha$$ increases at further distances from the mid-plane. Finally, we show that the outflow PAH emission reaches a local minimum in regions of the M 82 wind that are bright in X-ray emission. Our results are consistent cold gas in galactic outflows being launched via hierarchically structured plumes, and those small scale clouds are more likely to survive the wind environment when collected into the larger plume structure. 

Abstract We present a near-infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses >10⁴M_⊙. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of ≈1 pc and stellar masses up to 10⁶M_⊙. By comparing the color–color diagram to dust-freeyggdrasilstellar population models, we estimate that the star cluster candidates haveA_V∼ 3−24 mag, corresponding toA_2.5μm∼ 0.3−2.1 mag. There is still appreciable dust extinction toward these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function isβ= 1.9 ± 0.2, in excellent agreement with studies of star clusters in other galaxies. 

Abstract A compact source, G0.02467–0.0727, was detected in Atacama Large Millimeter/submillimeter Array 3 mm observations in continuum and very broad line emission. The continuum emission has a spectral indexα≈ 3.3, suggesting that the emission is from dust. The line emission is detected in several transitions of CS, SO, and SO₂and exhibits a line width FWHM ≈ 160 km s⁻¹. The line profile appears Gaussian. The emission is weakly spatially resolved, coming from an area on the sky ≲1″ in diameter (≲10⁴au at the distance of the Galactic center, GC). The centroid velocity isv_LSR≈ 40–50 km s⁻¹, which is consistent with a location in the GC. With multiple SO lines detected, and assuming local thermodynamic equilibrium (LTE) conditions, the gas temperature isT_LTE= 13 K, which is colder than seen in typical GC clouds, though we cannot rule out low-density, subthermally excited, warmer gas. Despite the high velocity dispersion, no emission is observed from SiO, suggesting that there are no strong (≳10 km s⁻¹) shocks in the molecular gas. There are no detections at other wavelengths, including X-ray, infrared, and radio. We consider several explanations for the millimeter ultra-broad-line object (MUBLO), including protostellar outflow, explosive outflow, a collapsing cloud, an evolved star, a stellar merger, a high-velocity compact cloud, an intermediate-mass black hole, and a background galaxy. Most of these conceptual models are either inconsistent with the data or do not fully explain them. The MUBLO is, at present, an observationally unique object. 

ABSTRACT Galactic bars can drive cold gas inflows towards the centres of galaxies. The gas transport happens primarily through the so-called bar dust lanes, which connect the galactic disc at kpc scales to the nuclear rings at hundreds of pc scales much like two gigantic galactic rivers. Once in the ring, the gas can fuel star formation activity, galactic outflows, and central supermassive black holes. Measuring the mass inflow rates is therefore important to understanding the mass/energy budget and evolution of galactic nuclei. In this work, we use CO datacubes from the PHANGS-ALMA survey and a simple geometrical method to measure the bar-driven mass inflow rate on to the nuclear ring of the barred galaxy NGC 1097. The method assumes that the gas velocity in the bar lanes is parallel to the lanes in the frame co-rotating with the bar, and allows one to derive the inflow rates from sufficiently sensitive and resolved position–position–velocity diagrams if the bar pattern speed and galaxy orientations are known. We find an inflow rate of $$\dot{M}=(3.0 \pm 2.1)\, \rm M_\odot \, yr^{-1}$$ averaged over a time span of 40 Myr, which varies by a factor of a few over time-scales of ∼10 Myr. Most of the inflow appears to be consumed by star formation in the ring, which is currently occurring at a star formation rate (SFR) of $$\simeq\!1.8\!-\!2 \, \rm M_\odot \, yr^{-1}$$, suggesting that the inflow is causally controlling the SFR in the ring as a function of time. 

Abstract We present new observations of the central 1 kpc of the M82 starburst obtained with the James Webb Space Telescope near-infrared camera instrument at a resolutionθ∼ 0.″05–0.″1 (∼1–2 pc). The data comprises images in three mostly continuum filters (F140M, F250M, and F360M), and filters that contain [Feii] (F164N), H₂v= 1 → 0 (F212N), and the 3.3μm polycyclic aromatic hydrocarbon (PAH) feature (F335M). We find prominent plumes of PAH emission extending outward from the central starburst region, together with a network of complex filamentary substructures and edge-brightened bubble-like features. The structure of the PAH emission closely resembles that of the ionized gas, as revealed in Paschenαand free–free radio emission. We discuss the origin of the structure, and suggest the PAHs are embedded in a combination of neutral, molecular, and photoionized gas. 

Abstract We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately (∼1 kpc) spatially resolved measurements of CO (1–0) and CO (2–1) intensity,I_CO, and mid-IR intensity,I_MIR, at 8, 12, 22, and 24μm. TheI_COversusI_MIRrelationship is reasonably described by a power law with slopes 0.7–1.2 and normalizationI_CO∼ 1 K km s⁻¹atI_MIR∼ 1 MJy sr⁻¹. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO (1–0) and CO (2–1) allow us to infer that $R_{21}\propto I_{\mathrm{MIR}}^{0.2}$, in good agreement with other work. The 8μm and 12μm bands, with strong polycyclic aromatic hydrocarbon (PAH) features, show steeper CO versus mid-IR slopes than the 22 and 24μm, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass (M_⋆) and anticorrelates with star formation rate/M_⋆. At ∼1 kpc resolution, the first four PHANGS–JWST targets show CO-to-mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities.